Optical mineralogy is the study of minerals and rocks by measuring their optical properties. Most commonly, rock and mineral samples are prepared as thin sections or grain mounts for study in the laboratory with a petrographic microscope. Optical mineralogy is used to identify the mineralogical composition of geological materials in order to help reveal their origin and evolution.
Some of the properties and techniques used include:
* Refractive index
* Birefringence
* Michel-Lévy Interference colour chart
* Pleochroism
* Extinction angle
* Conoscopic interference pattern (Interference figure)
* Becke line test
* Optical relief
* Sign of elongation (Length fast vs. length slow)
* Wave plate
History
William Nicol, whose name is associated with the creation of the Nicol prism, seems to have been the first to prepare thin slices of mineral substances, and his methods were applied by Henry Thronton Maire Witham (1831) to the study of plant petrifactions. This method, of such far-reaching importance in petrology, was not at once made use of for the systematic investigation of rocks, and it was not until 1858 that Henry Clifton Sorby pointed out its value. Meanwhile the optical study of sections of crystals had been advanced by Sir David Brewster and other physicists and mineralogists and it only remained to apply their methods to the minerals visible in rock sections.[1]
[edit] Sections
A good rock-section should be about one-thousandth of an inch (30 microns) in thickness, and is by no means very difficult to make. A thin splinter of the rock, about as large as a halfpenny may be taken; it should be as fresh as possible and free from obvious cracks. By grinding it on a plate of planed steel or cast iron with a little fine carborundum it is soon rendered flat on one side and is then transferred to a sheet of plate glass and smoothed with the very finest emery till all minute pits and roughnesses are removed and the surface is a uniform plane. The rock-chip is then washed, and placed on a copper or iron plate which is heated by a spirit or gas lamp. A microscopic glass slip is also warmed on this plate with a drop of viscous natural Canada balsam on its surface. The more volatile ingredients of the balsam are dispelled by the heat, and when that is accomplished the smooth, dry, warm rock is pressed firmly into contact with the glass plate so that the film of balsam intervening may be as thin as possible and free from air-bubbles. The preparation is allowed to cool and then the rock chip is again ground down as before, first with carborundum and, when it becomes transparent, with fine emery till the desired thickness is obtained. It is then cleaned, again heated with a little more balsam, and covered with a cover glass. The labor of grinding the first surface may be avoided by cutting off a smooth slice with an iron disk armed with crushed diamond powder. A second application of the slitter after the first face is smoothed and cemented to the glass will in expert hands leave a rock-section so thin as to be already transparent. In this way the preparation of a section may require only twenty minutes.[1]
[edit] Microscope
Photomicrograph of a volcanic sand grain; upper picture is plane-polarized light, bottom picture is cross-polarized light, scale box at left-center is 0.25 millimeter.
The microscope employed is usually one which is provided with a rotating stage beneath which there is a polarizer, while above the objective or the eyepiece an analyzer is mounted; alternatively the stage may be fixed and the polarizing and analyzing prisms may be capable of simultaneous rotation by means of toothed wheels and a connecting-rod. If ordinary light and not polarized light is desired, both prisms may be withdrawn from the axis of the instrument; if the polarizer only is inserted the light transmitted is plane polarized; with both prisms in position the slide is viewed in cross-polarized light, also known as "crossed nicols." A microscopic rock-section in ordinary light, if a suitable magnification (say 30) be employed, is seen to consist of grains or crystals varying in color, size and shape.[1]
[edit] Characters of minerals
Some minerals are colorless and transparent (quartz, calcite, feldspar, muscovite, etc.), others are yellow or brown (rutile, tourmaline, biotite), green (diopside, hornblende, chlorite), blue (glaucophane), pink (garnet), etc. The same mineral may present a variety of colors, in the same or different rocks, and these colors may be arranged in zones parallel to the surfaces of the crystals. Thus tourmaline may be brown, yellow, pink, blue, green, violet, grey, or colorless, but every mineral has one or more characteristic, most common tints. The shapes of the crystals determine in a general way the outlines of the sections of them presented on the slides. If the mineral has one or more good cleavages they will be indicated by systems of cracks. The refractive index is also clearly shown by the appearance of the section, which are rough, with well-defined borders if they have a much stronger refraction than the medium in which they are mounted. Some minerals decompose readily and become turbid and semi-transparent (e.g. feldspar); others remain always perfectly fresh and clear (e.g. quartz), others yield characteristic secondary products (such as green chlorite after biotite). The inclusions in the crystals (both solid and fluid) are of great interest; one mineral may enclose another, or may contain spaces occupied by glass, by fluids or by gases.[1]
Microstructure
Lastly the structure of the rock, that is to say, the relation of its components to one another, is usually clearly indicated, whether it be fragmented or massive; the presence of glassy matter in contradistinction to a completely crystalline or "holo-crystalline" condition; the nature and origin of organic fragments; banding, foliation or lamination; the pumiceous or porous structure of many lavas; these and many other characters, though often not visible in the hand specimens of a rock, are rendered obvious by the examination of a microscopic section. Many refined methods of observation may be introduced, such as the measurement of the size of the elements of the rock by the help of micrometers; their relative proportions by means of a glass plate ruled in small squares; the angles between cleavages or faces seen in section by the use of the rotating graduated stage, and the estimation of the refractive index of the mineral by comparison with those of different mounting media.[1]
Pleochroism
Main article: Pleochroism
Further information is obtained by inserting the polarizer and rotating the section. The light vibrates now only in one plane, and in passing through doubly refracting crystals in the slide, is, speaking generally, broken up into rays, which vibrate at right angles to one another. In many colored minerals such as biotite, hornblende, tourmaline, chlorite, these two rays have different colors, and when a section containing any of these minerals is rotated the change of color is often very striking. This property, known as "pleochroism" is of great value in the determination of rock-making minerals.
Pleochroism is often especially intense in small spots which surround minute enclosures of other minerals, such as zircon and epidote, these are known as "pleochroic halos."[1]
Double refraction
If the analyzer be now inserted in such a position that it is crossed relatively to the polarizer the field of view will be dark where there are no minerals, or where the light passes through isotropic substances such as glass, liquids and cubic crystals. All other crystalline bodies, being doubly refracting, will appear bright in some position as the stage is rotated. The only exception to this rule is provided by sections which are perpendicular to the optic axes of birefringent crystals; these remain dark or nearly dark during a whole rotation, and as will be seen later, their investigation is of special importance.[1]
Extinction
The doubly refracting mineral sections, however, will in all cases appear black in certain positions as the stage is rotated. They are said to go "extinct" when this takes place. If we note these positions we may measure the angle between them and any cleavages, faces or other structures of the crystal by means of the rotating stage. These angles are characteristic of the system to which the mineral belongs and often of the mineral species itself (see Crystallography). To facilitate measurement of extinction angles various kinds of eyepieces have been devised, some having a stereoscopic calcite plate, others with two or four plates of quartz cemented together; these are often found to give more exact results than are obtained by observing merely the position in which the mineral section is most completely dark between crossed nicols.
The mineral sections when not extinguished are not only bright but are colored and the colors they show depend on several factors, the most important of which is the strength of the double refraction. If all the sections are of the same thickness as is nearly true of well-made slides, the minerals with strongest double refraction yield the highest polarization colors. The order in which the colors are arranged in what is known as Newton's scale, the lowest being dark grey, then grey, white, yellow, orange, red, purple, blue and so on. The difference between the refractive indexes of the ordinary and the extraordinary ray in quartz is .009, and in a rock-section about 1/500 of an inch thick this mineral gives grey and white polarization colours; nepheline with weaker double refraction gives dark grey; augite on the other hand will give red and blue, while calcite with the stronger double refraction will appear pinkish or greenish white. All sections of the same mineral, however, will not have the same color; it was stated above that sections perpendicular to an optic axis will be nearly black, and, in general, the more nearly any section approaches this direction the lower its polarization colors will be. By taking the average, or the highest color given by any mineral, the relative value of its double refraction can be estimated; or if the thickness of the section be precisely known the difference between the two refractive indexes can be ascertained. If the slides be thick the colors will be on the whole higher than in thin slides.
It is often important to find out whether of the two axes of elasticity (or vibration traces) in the section is that of greater elasticity (or lesser refractive index). The quartz wedge or selenite plate enables us to do this. Suppose a doubly refracting mineral section so placed that it is "extinguished"; if now is rotated through 45 degrees it will be brightly illuminated. If the quartz wedge be passed across it so that the long axis of the wedge is parallel to the axis of elasticity in the section the polarization colors will rise or fall. If they rise the axes of greater elasticity in the two minerals are parallel; if they sink the axis of greater elasticity in the one is parallel to that of lesser elasticity in the other. In the latter case by pushing the wedge sufficiently far complete darkness or compensation will result. Selenite wedges, selenite plates, mica wedges and mica plates are also used for this purpose. A quartz wedge also may be calibrated by determining the amount of double refraction in all parts of its length. If now it be used to produce compensation or complete extinction in any doubly refracting mineral section, we can ascertain what is the strength of the double refraction of the section because it is obviously equal and opposite to that of a known part of the quartz wedge.
A further refinement of microscopic methods consists of the use of strongly convergent polarized light (konoscopic methods). This is obtained by a wide angled achromatic condenser above the polarizer, and a high power microscopic objective. Those sections are most useful which are perpendicular to an optic axis, and consequently remain dark on rotation. If they belong to uniaxial crystals they show a dark cross or convergent light between crossed nicols, the bars of which remain parallel to the wires in the field of the eyepiece. Sections perpendicular to an optic axis of a biaxial mineral under the same conditions show a dark bar which on rotation becomes curved to a hyperbolic shape. If the section is perpendicular to a "bisectrix" (see Crystallography) a black cross is seen which on rotation opens out to form two hyperbolas, the apices of which are turned towards one another. The optic axes emerge at the apices of the hyperbolas and may be surrounded by colored rings, though owing to the thinness of minerals in rock sections these are only seen when the double refraction of the mineral is strong. The distance between the axes as seen in the field of the microscope depends partly on the axial angle of the crystal and partly on the numerical aperture of the objective. If it is measured by means of eye-piece micrometer, the optic axial angle of the mineral can be found by a simple calculation. The quartz wedge, quarter mica plate or selenite plate permit the determination of the positive or negative character of the crystal by the changes in the color or shape of the figures observed in the field. These operations are precisely similar to those employed by the mineralogist in the examination of plates cut from crystals. It is sufficient to point out that the petrological microscope in its modern development is an optical instrument of great precision, enabling us to determine physical constants of crystallized substances as well as serving to produce magnified images like the ordinary microscope. A great variety of accessory apparatus has been devised to fit it for these special uses.
Examination of rock powders
Although rocks are now studied principally in microscopic sections the investigation of fine crushed rock powders, which was the first branch of microscopic petrology to receive attention, is by no means discontinued. The modern optical methods are perfectly applicable to transparent mineral fragments of any kind. Minerals are almost as easily determined in powder as in section, but it is otherwise with rocks, as the structure or relation of the components to one another, which is an element of great importance in the study of the history and classification or rocks, is almost completely destroyed by grinding them to powder.
Thursday, March 18, 2010
Petroleum geology
Sedimentary basin analysis
Petroleum geology is principally concerned with the evaluation of seven key elements in sedimentary basins:
A structural trap, where a fault has juxtaposed a porous and permeable reservoir against an impermeable seal. Oil (shown in red) accumulates against the seal, to the depth of the base of the seal. Any further oil migrating in from the source will escape to the surface and seep.
* Source
* Reservoir
* Seal
* Trap
* Timing
* Maturation
* Migration
In general, all these elements must be assessed via a limited 'window' into the subsurface world, provided by one (or possibly more) exploration wells. These wells present only a 1-dimensional segment through the Earth and the skill of inferring 3-dimensional characteristics from them is one of the most fundamental in petroleum geology. Recently, the availability of cheap and high quality 3D seismic data (from reflection seismology) has greatly aided the accuracy of such interpretation. The following section discusses these elements in brief. For a more in-depth treatise, see the second half of this article below.
Evaluation of the source uses the methods of geochemistry to quantify the nature of organic-rich rocks which contain the precursors to hydrocarbons, such that the type and quality of expelled hydrocarbon can be assessed.
The reservoir is a porous and permeable lithological unit or set of units that holds the hydrocarbon reserves. Analysis of reservoirs at the simplest level requires an assessment of their porosity (to calculate the volume of in situ hydrocarbons) and their permeability (to calculate how easily hydrocarbons will flow out of them). Some of the key disciplines used in reservoir analysis are the fields of stratigraphy, sedimentology, and reservoir engineering.
The seal, or cap rock, is a unit with low permeability that impedes the escape of hydrocarbons from the reservoir rock. Common seals include evaporites, chalks and shales. Analysis of seals involves assessment of their thickness and extent, such that their effectiveness can be quantified.
The trap is the stratigraphic or structural feature that ensures the juxtaposition of reservoir and seal such that hydrocarbons remain trapped in the subsurface, rather than escaping (due to their natural buoyancy) and being lost.
Analysis of maturation involves assessing the thermal history of the source rock in order to make predictions of the amount and timing of hydrocarbon generation and expulsion.
Finally, careful studies of migration reveal information on how hydrocarbons move from source to reservoir and help quantify the source (or kitchen) of hydrocarbons in a particular area.
Major subdisciplines in petroleum geology
Several major subdisciplines exist in petroleum geology specifically to study the seven key elements discussed above.
Analysis of source rocks
In terms of source rock analysis, several facts need to be established. Firstly, the question of whether there actually is any source rock in the area must be answered. Delineation and identification of potential source rocks depends on studies of the local stratigraphy, palaeogeography and sedimentology to determine the likelihood of organic-rich sediments having been deposited in the past.
If the likelihood of there being a source rock is thought to be high, the next matter to address is the state of thermal maturity of the source, and the timing of maturation. Maturation of source rocks (see diagenesis and fossil fuels) depends strongly on temperature, such that the majority of oil generation occurs in the 60° to 120°C range. Gas generation starts at similar temperatures, but may continue up beyond this range, perhaps as high as 200°C. In order to determine the likelihood of oil/gas generation, therefore, the thermal history of the source rock must be calculated. This is performed with a combination of geochemical analysis of the source rock (to determine the type of kerogens present and their maturation characteristics) and basin modelling methods, such as back-stripping, to model the thermal gradient in the sedimentary column.
Analysis of reservoir
The existence of a reservoir rock (typically, sandstones and fractured limestones) is determined through a combination of regional studies (i.e. analysis of other wells in the area), stratigraphy and sedimentology (to quantify the pattern and extent of sedimentation) and seismic interpretation. Once a possible hydrocarbon reservoir is identified, the key physical characteristics of a reservoir that are of interest to a hydrocarbon explorationist are its porosity and permeability. Traditionally, these were determined through the study of hand specimens, contiguous parts of the reservoir that outcrop at the surface and by the technique of formation evaluation using wireline tools passed down the well itself. Modern advances in seismic data acquisition and processing have meant that seismic attributes of subsurface rocks are readily available and can be used to infer physical/sedimentary properties of the rocks themselves.
Petroleum geology is principally concerned with the evaluation of seven key elements in sedimentary basins:
A structural trap, where a fault has juxtaposed a porous and permeable reservoir against an impermeable seal. Oil (shown in red) accumulates against the seal, to the depth of the base of the seal. Any further oil migrating in from the source will escape to the surface and seep.
* Source
* Reservoir
* Seal
* Trap
* Timing
* Maturation
* Migration
In general, all these elements must be assessed via a limited 'window' into the subsurface world, provided by one (or possibly more) exploration wells. These wells present only a 1-dimensional segment through the Earth and the skill of inferring 3-dimensional characteristics from them is one of the most fundamental in petroleum geology. Recently, the availability of cheap and high quality 3D seismic data (from reflection seismology) has greatly aided the accuracy of such interpretation. The following section discusses these elements in brief. For a more in-depth treatise, see the second half of this article below.
Evaluation of the source uses the methods of geochemistry to quantify the nature of organic-rich rocks which contain the precursors to hydrocarbons, such that the type and quality of expelled hydrocarbon can be assessed.
The reservoir is a porous and permeable lithological unit or set of units that holds the hydrocarbon reserves. Analysis of reservoirs at the simplest level requires an assessment of their porosity (to calculate the volume of in situ hydrocarbons) and their permeability (to calculate how easily hydrocarbons will flow out of them). Some of the key disciplines used in reservoir analysis are the fields of stratigraphy, sedimentology, and reservoir engineering.
The seal, or cap rock, is a unit with low permeability that impedes the escape of hydrocarbons from the reservoir rock. Common seals include evaporites, chalks and shales. Analysis of seals involves assessment of their thickness and extent, such that their effectiveness can be quantified.
The trap is the stratigraphic or structural feature that ensures the juxtaposition of reservoir and seal such that hydrocarbons remain trapped in the subsurface, rather than escaping (due to their natural buoyancy) and being lost.
Analysis of maturation involves assessing the thermal history of the source rock in order to make predictions of the amount and timing of hydrocarbon generation and expulsion.
Finally, careful studies of migration reveal information on how hydrocarbons move from source to reservoir and help quantify the source (or kitchen) of hydrocarbons in a particular area.
Major subdisciplines in petroleum geology
Several major subdisciplines exist in petroleum geology specifically to study the seven key elements discussed above.
Analysis of source rocks
In terms of source rock analysis, several facts need to be established. Firstly, the question of whether there actually is any source rock in the area must be answered. Delineation and identification of potential source rocks depends on studies of the local stratigraphy, palaeogeography and sedimentology to determine the likelihood of organic-rich sediments having been deposited in the past.
If the likelihood of there being a source rock is thought to be high, the next matter to address is the state of thermal maturity of the source, and the timing of maturation. Maturation of source rocks (see diagenesis and fossil fuels) depends strongly on temperature, such that the majority of oil generation occurs in the 60° to 120°C range. Gas generation starts at similar temperatures, but may continue up beyond this range, perhaps as high as 200°C. In order to determine the likelihood of oil/gas generation, therefore, the thermal history of the source rock must be calculated. This is performed with a combination of geochemical analysis of the source rock (to determine the type of kerogens present and their maturation characteristics) and basin modelling methods, such as back-stripping, to model the thermal gradient in the sedimentary column.
Analysis of reservoir
The existence of a reservoir rock (typically, sandstones and fractured limestones) is determined through a combination of regional studies (i.e. analysis of other wells in the area), stratigraphy and sedimentology (to quantify the pattern and extent of sedimentation) and seismic interpretation. Once a possible hydrocarbon reservoir is identified, the key physical characteristics of a reservoir that are of interest to a hydrocarbon explorationist are its porosity and permeability. Traditionally, these were determined through the study of hand specimens, contiguous parts of the reservoir that outcrop at the surface and by the technique of formation evaluation using wireline tools passed down the well itself. Modern advances in seismic data acquisition and processing have meant that seismic attributes of subsurface rocks are readily available and can be used to infer physical/sedimentary properties of the rocks themselves.
Oceanography
Oceanography (compound of the Greek words ωκεανός meaning "ocean" and γράφω meaning "to write"), also called oceanology or marine science, is the branch of Earth science that studies the ocean. It covers a wide range of topics, including marine organisms and ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamics; plate tectonics and the geology of the sea floor; and fluxes of various chemical substances and physical properties within the ocean and across its boundaries. These diverse topics reflect multiple disciplines that oceanographers blend to further knowledge of the world ocean and understanding of processes within it: biology, chemistry, geology, meteorology, and physics.
Branches
The study of oceanography is divided into a number of branches:
* Biological oceanography, or marine biology, is the study of the plants, animals and microbes of the oceans and their ecological interaction with the ocean;
* Chemical oceanography, or marine chemistry, is the study of the chemistry of the ocean and its chemical interaction with the atmosphere;
* Geological oceanography, or marine geology, is the study of the geology of the ocean floor including plate tectonics;
* Physical oceanography, or marine physics, studies the ocean's physical attributes including temperature-salinity structure, mixing, waves, internal waves, surface tides, internal tides, and currents. Of particular interest is the behavior of sound (acoustical oceanography), light (optical oceanography) and radio waves in the ocean.
These branches reflect the fact that many oceanographers are first trained in the exact sciences or mathematics and then focus on applying their interdisciplinary knowledge, skills and abilities to oceanography.[1]
Data derived from the work of Oceanographers is used in marine engineering, in the design and building of oil platforms, ships, harbours, and other structures that allow us to use the ocean safely.[2]
Oceanographic data management is the discipline ensuring that oceanographic data both past and present are available to researchers.
History
Man first began to acquire knowledge of the waves and currents of the seas and oceans in pre-historic times. Observations on tides are recorded by Aristotle and Strabo. Early modern exploration of the oceans was primarily for cartography and mainly limited to its surfaces and of the creatures that fishermen brought up in nets, though depth soundings by lead line were taken.
Map of the Gulf Stream by Benjamin Franklin, 1769-1770. Courtesy of the NOAA Photo Library.
Although Juan Ponce de Leon in 1513 first identified the Gulf Stream, and the current was well-known to mariners, Benjamin Franklin made the first scientific study of it and gave it its name. Franklin measured water temperatures during several Atlantic crossings and correctly explained the Gulf Stream's cause. Franklin and Timothy Folger printed the first map of the Gulf Stream in 1769-1770.[3][4]
When Louis Antoine de Bougainville, who voyaged between 1766 and 1769, and James Cook, who voyaged from 1768 to 1779, carried out their explorations in the South Pacific, information on the oceans themselves formed part of the reports. James Rennell wrote the first scientific textbooks about currents in the Atlantic and Indian oceans during the late 18th and at the beginning of 19th century. Sir James Clark Ross took the first modern sounding in deep sea in 1840, and Charles Darwin published a paper on reefs and the formation of atolls as a result of the second voyage of HMS Beagle in 1831-6. Robert FitzRoy published a report in four volumes of the three voyages of the Beagle. In 1841–1842 Edward Forbes undertook dredging in the Aegean Sea that founded marine ecology.
As first superintendent of the United States Naval Observatory (1842–1861) Matthew Fontaine Maury devoted his time to the study of marine meteorology, navigation, and charting prevailing winds and currents. His Physical Geography of the Sea, 1855 was the first textbook of oceanography. Many nations sent oceanographic observations to Maury at the Naval Observatory, where he and his colleagues evaluated the information and gave the results worldwide distribution. [5]
The steep slope beyond the continental shelves was discovered in 1849. The first successful laying of transatlantic telegraph cable in August 1858 confirmed the presence of an underwater "telegraphic plateau" mid-ocean ridge. After the middle of the 19th century, scientific societies were processing a flood of new terrestrial botanical and zoological information. European natural historians began to sense the lack of more than anecdotal knowledge of the oceans.
In 1871, under the recommendations of the Royal Society of London, the British government sponsored an expedition to explore world's oceans and conduct scientific investigations. Under that sponsorship the Scots Charles Wyville Thompson and Sir John Murray launched the Challenger expedition (1872–1876). The results of this were published in 50 volumes covering biological, physical and geological aspects. 4417 new species were discovered.
Other European and American nations also sent out scientific expeditions (as did private individuals and institutions). The first purpose built oceanographic ship, the "Albatros" was built in 1882. The four-month 1910 North Atlantic expedition headed by Sir John Murray and Johan Hjort was at that time the most ambitious research oceanographic and marine zoological project ever, and led to the classic 1912 book The Depths of the Ocean.
Oceanographic institutes dedicated to the study of oceanography were founded. In the United States, these included the Scripps Institution of Oceanography in 1892, Woods Hole Oceanographic Institution in 1930, Virginia Institute of Marine Science in 1938, Lamont-Doherty Earth Observatory at Columbia University, and the School of Oceanography at University of Washington. In Britain, there is a major research institution: National Oceanography Centre, Southampton which is the successor to the Institute of Oceanography. In Australia, CSIRO Marine and Atmospheric Research, known as CMAR, is a leading center. In 1921 the International Hydrographic Bureau (IHB) was formed in Monaco.
Ocean currents (1911)
In 1893 Fridtjof Nansen allowed his ship "Fram" to be frozen in the Arctic ice. As a result he was able to obtain oceanographic data as well as meteorological and astronomical data. The first international organization of oceanography was created in 1902 as the International Council for the Exploration of the Sea.
The first acoustic measurement of sea depth was made in 1914. Between 1925 and 1927 the "Meteor" expedition gathered 70,000 ocean depth measurements using an echo sounder, surveying the Mid atlantic ridge. The Great Global Rift, running along the Mid Atlantic Ridge, was discovered by Maurice Ewing and Bruce Heezen in 1953 while the mountain range under the Arctic was found in 1954 by the Arctic Institute of the USSR. The theory of seafloor spreading was developed in 1960 by Harry Hammond Hess. The Ocean Drilling Project started in 1966. Deep sea vents were discovered in 1977 by John Corlis and Robert Ballard in the submersible "Alvin".
In the 1950s Auguste Piccard invented the bathyscaphe and used the "Trieste" to investigate the ocean's depths. The nuclear submarine Nautilus made the first journey under the ice to the North Pole in 1958. In 1962 there was the first deployment of FLIP (Floating Instrument Platform), a 355 foot spar buoy.
Then in 1966, the U.S. Congress created a National Council for Marine Resources and Engineering Development. NOAA was put in charge of exploring and studying all aspects of Oceanography in the USA. It also enabled the National Science Foundation to award Sea Grant College funding to multi-disciplinary researchers in the field of oceanography.[6][7]
From the 1970s there has been much emphasis on the application of large scale computers to oceanography to allow numerical predictions of ocean conditions and as a part of overall environmental change prediction. An oceanographic buoy array was established in the Pacific to allow prediction of El Niño events.
1990 saw the start of the World Ocean Circulation Experiment (WOCE) which continued until 2002. Geosat seafloor mapping data became available in 1995.
In 1942 Sverdrup and Fleming published "The Ocean" which was a major landmark. "The Sea" (in three volumes covering physical oceanography, seawater and geology) edited by M.N. Hill was published in 1962 while the "Encyclopedia of Oceanography" by Rhodes Fairbridge was published in 1966.
Ocean and atmosphere connections
The study of the oceans is intimately linked to understanding global climate changes, potential global warming and related biosphere concerns. The atmosphere and ocean are linked because of evaporation and precipitation as well as thermal flux (and solar insolation). Wind stress is a major driver of ocean currents while the ocean is a sink for atmospheric carbon dioxide.
Our planet is invested with two great oceans; one visible, the other invisible; one underfoot, the other overhead; one entirely envelopes it, the other covers about two thirds of its surface.
Branches
The study of oceanography is divided into a number of branches:
* Biological oceanography, or marine biology, is the study of the plants, animals and microbes of the oceans and their ecological interaction with the ocean;
* Chemical oceanography, or marine chemistry, is the study of the chemistry of the ocean and its chemical interaction with the atmosphere;
* Geological oceanography, or marine geology, is the study of the geology of the ocean floor including plate tectonics;
* Physical oceanography, or marine physics, studies the ocean's physical attributes including temperature-salinity structure, mixing, waves, internal waves, surface tides, internal tides, and currents. Of particular interest is the behavior of sound (acoustical oceanography), light (optical oceanography) and radio waves in the ocean.
These branches reflect the fact that many oceanographers are first trained in the exact sciences or mathematics and then focus on applying their interdisciplinary knowledge, skills and abilities to oceanography.[1]
Data derived from the work of Oceanographers is used in marine engineering, in the design and building of oil platforms, ships, harbours, and other structures that allow us to use the ocean safely.[2]
Oceanographic data management is the discipline ensuring that oceanographic data both past and present are available to researchers.
History
Man first began to acquire knowledge of the waves and currents of the seas and oceans in pre-historic times. Observations on tides are recorded by Aristotle and Strabo. Early modern exploration of the oceans was primarily for cartography and mainly limited to its surfaces and of the creatures that fishermen brought up in nets, though depth soundings by lead line were taken.
Map of the Gulf Stream by Benjamin Franklin, 1769-1770. Courtesy of the NOAA Photo Library.
Although Juan Ponce de Leon in 1513 first identified the Gulf Stream, and the current was well-known to mariners, Benjamin Franklin made the first scientific study of it and gave it its name. Franklin measured water temperatures during several Atlantic crossings and correctly explained the Gulf Stream's cause. Franklin and Timothy Folger printed the first map of the Gulf Stream in 1769-1770.[3][4]
When Louis Antoine de Bougainville, who voyaged between 1766 and 1769, and James Cook, who voyaged from 1768 to 1779, carried out their explorations in the South Pacific, information on the oceans themselves formed part of the reports. James Rennell wrote the first scientific textbooks about currents in the Atlantic and Indian oceans during the late 18th and at the beginning of 19th century. Sir James Clark Ross took the first modern sounding in deep sea in 1840, and Charles Darwin published a paper on reefs and the formation of atolls as a result of the second voyage of HMS Beagle in 1831-6. Robert FitzRoy published a report in four volumes of the three voyages of the Beagle. In 1841–1842 Edward Forbes undertook dredging in the Aegean Sea that founded marine ecology.
As first superintendent of the United States Naval Observatory (1842–1861) Matthew Fontaine Maury devoted his time to the study of marine meteorology, navigation, and charting prevailing winds and currents. His Physical Geography of the Sea, 1855 was the first textbook of oceanography. Many nations sent oceanographic observations to Maury at the Naval Observatory, where he and his colleagues evaluated the information and gave the results worldwide distribution. [5]
The steep slope beyond the continental shelves was discovered in 1849. The first successful laying of transatlantic telegraph cable in August 1858 confirmed the presence of an underwater "telegraphic plateau" mid-ocean ridge. After the middle of the 19th century, scientific societies were processing a flood of new terrestrial botanical and zoological information. European natural historians began to sense the lack of more than anecdotal knowledge of the oceans.
In 1871, under the recommendations of the Royal Society of London, the British government sponsored an expedition to explore world's oceans and conduct scientific investigations. Under that sponsorship the Scots Charles Wyville Thompson and Sir John Murray launched the Challenger expedition (1872–1876). The results of this were published in 50 volumes covering biological, physical and geological aspects. 4417 new species were discovered.
Other European and American nations also sent out scientific expeditions (as did private individuals and institutions). The first purpose built oceanographic ship, the "Albatros" was built in 1882. The four-month 1910 North Atlantic expedition headed by Sir John Murray and Johan Hjort was at that time the most ambitious research oceanographic and marine zoological project ever, and led to the classic 1912 book The Depths of the Ocean.
Oceanographic institutes dedicated to the study of oceanography were founded. In the United States, these included the Scripps Institution of Oceanography in 1892, Woods Hole Oceanographic Institution in 1930, Virginia Institute of Marine Science in 1938, Lamont-Doherty Earth Observatory at Columbia University, and the School of Oceanography at University of Washington. In Britain, there is a major research institution: National Oceanography Centre, Southampton which is the successor to the Institute of Oceanography. In Australia, CSIRO Marine and Atmospheric Research, known as CMAR, is a leading center. In 1921 the International Hydrographic Bureau (IHB) was formed in Monaco.
Ocean currents (1911)
In 1893 Fridtjof Nansen allowed his ship "Fram" to be frozen in the Arctic ice. As a result he was able to obtain oceanographic data as well as meteorological and astronomical data. The first international organization of oceanography was created in 1902 as the International Council for the Exploration of the Sea.
The first acoustic measurement of sea depth was made in 1914. Between 1925 and 1927 the "Meteor" expedition gathered 70,000 ocean depth measurements using an echo sounder, surveying the Mid atlantic ridge. The Great Global Rift, running along the Mid Atlantic Ridge, was discovered by Maurice Ewing and Bruce Heezen in 1953 while the mountain range under the Arctic was found in 1954 by the Arctic Institute of the USSR. The theory of seafloor spreading was developed in 1960 by Harry Hammond Hess. The Ocean Drilling Project started in 1966. Deep sea vents were discovered in 1977 by John Corlis and Robert Ballard in the submersible "Alvin".
In the 1950s Auguste Piccard invented the bathyscaphe and used the "Trieste" to investigate the ocean's depths. The nuclear submarine Nautilus made the first journey under the ice to the North Pole in 1958. In 1962 there was the first deployment of FLIP (Floating Instrument Platform), a 355 foot spar buoy.
Then in 1966, the U.S. Congress created a National Council for Marine Resources and Engineering Development. NOAA was put in charge of exploring and studying all aspects of Oceanography in the USA. It also enabled the National Science Foundation to award Sea Grant College funding to multi-disciplinary researchers in the field of oceanography.[6][7]
From the 1970s there has been much emphasis on the application of large scale computers to oceanography to allow numerical predictions of ocean conditions and as a part of overall environmental change prediction. An oceanographic buoy array was established in the Pacific to allow prediction of El Niño events.
1990 saw the start of the World Ocean Circulation Experiment (WOCE) which continued until 2002. Geosat seafloor mapping data became available in 1995.
In 1942 Sverdrup and Fleming published "The Ocean" which was a major landmark. "The Sea" (in three volumes covering physical oceanography, seawater and geology) edited by M.N. Hill was published in 1962 while the "Encyclopedia of Oceanography" by Rhodes Fairbridge was published in 1966.
Ocean and atmosphere connections
The study of the oceans is intimately linked to understanding global climate changes, potential global warming and related biosphere concerns. The atmosphere and ocean are linked because of evaporation and precipitation as well as thermal flux (and solar insolation). Wind stress is a major driver of ocean currents while the ocean is a sink for atmospheric carbon dioxide.
Our planet is invested with two great oceans; one visible, the other invisible; one underfoot, the other overhead; one entirely envelopes it, the other covers about two thirds of its surface.
Volcanology
Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma, and related geological, geophysical and geochemical phenomena. The term volcanology is derived from the Latin word vulcan, which means the Roman god of fire.
Volcanologist examining tephra horizons in south-central Iceland.
A volcanologist is a person who studies the formation of volcanoes, and their current and historic eruptions. Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions, collect eruptive products including tephra (such as ash or pumice), rock and lava samples. One major focus of enquiry is the prediction of eruptions; there is currently no accurate way to do this, but predicting eruptions, like predicting earthquakes, could save many lives.
History of volcanology
Volcanology has an extensive history. The earliest known recording of a volcanic eruption may be on a wall painting dated to about 7000 B.C.E. found at the Neolithic site at Çatal Höyük (now known as Çatalhöyük), in Anatolia, Turkey. This painting has been interpreted as a depiction of an erupting volcano, with a cluster of houses below shows a twin peaked volcano in eruption, with a town at its base (though archaeologists now question this interpretation [1]). The volcano may be either Hasan Dağ, or its smaller neighbour, Melendiz Dağ. [2]
[edit] Mythical explanations
The classical world of Greece and the early Roman Empire explained volcanoes as the work of the gods as science and alchemy had no explanation for their existence. Grecian myths and tales tell of Atlantis, a fabled island which sank into the sea. Plato (428-348 B.C.) told of the disappearance of a vast island and its powerful civilization, the Atlanteans, in two of his dialogues, Critias and Timaeus. It is now considered that the island of Thera, now Santorini, in the Aegean Sea, was destroyed by a tremendous series of volcanic explosions around 1620 B.C., with ash falls of up to a foot deep recorded in Turkey. The explosion of Thera sent colossal tsunamis, estimated at 100 feet height, racing across the Aegean, and the southern coast of Crete. Other recordings of the Thera eruption spawned Greek myths, namely the Deucalion, in which Poseidon, god of the sea, took revenge upon Zeus by inundating Attica, Argolis, Salonika, Rhodes and the coast of Lycia (Turkey) to Sicily.
Greeks also considered that Hephaestus, the god of fire, sat below the volcano Etna, forging the weapons of Zeus. His minions, the cyclops with their single staring eye, may be an allegory to the round craters and cones of a volcano. Indeed, the Greek word used to describe volcanoes was etna, or hiera, after Heracles, the son of Zeus. The Roman poet Virgil, in interpreting the Greek mythos, held that the hero Enceladus was buried beneath Etna by the goddess Athena as punishment for disobeying the gods; the mountain's rumblings were his tormented cries, the flames his breath and the tremors his railing against the bars of his prison. Enceladus' brother Mimas was buried beneath Vesuvius by Hephaestus, and the blood of other defeated giants welled up in the Phlegrean Fields surrounding Vesuvius.
Tribal legends of volcanoes abound from the Pacific Ring of Fire and the Americas, usually invoking the forces of the supernatural or the divine to explain the violent outbursts of volcanoes. Taranaki and Tongariro, according to Māori mythology, were lovers who fell in love with Pihanga, and a spiteful jealous fight ensued. Māori will not to this day live between Tongariro and Taranaki for fear of the dispute flaring up again.
Greco-Roman science
Eruption of Vesuvius in 1822. The eruption of AD 79 would have appeared very similar.
The first attempt at a scientific explanation of volcanoes was undertaken by the Greek philosopher Empedocles (c. 490-430 B.C.), who saw the world divided into four elemental forces, of Earth, Air, Fire and Water. Volcanoes, Empedocles maintained, were the manifestation of Elemental Fire. Plato contended that channels of hot and cold waters flow in inexhaustible quantities through subterranean rivers. In the depths of the earth snakes a vast river of fire, the Pyriphlegethon, which feeds all the world's volcanoes. Aristotle considered underground fire as the result of "the...friction of the wind when it plunges into narrow passages."
Wind would play a key role in explanations of volcanoes until the 16th century. Lucretius, a Roman philosopher, claimed Etna was completely hollow and the fires of the underground driven by a fierce wind circulating near sea level. Ovid believed that the flame was fed from "fatty foods" and eruptions stopped when the food ran out. Vitruvius contended that sulfur, alum and bitumen fed the deep fires. Observations by Pliny the Elder noted the presence of earthquakes preceded an eruption; he died in the eruption of Vesuvius in 79 AD while investigating it at Stabiae. His nephew, Pliny the Younger gave detailed descriptions of the eruption in which his uncle died, attributing his death to the effects of toxic gases. Such eruptions have been named Plinian in honour of the two authors.
Christian mythology
The study of volcanology was not advanced much between the days of Plato and Hutton. The Christian world explained volcanoes by a multitude of prescientific notions, but it was also thought they were the work of Satan or the wrath of God, and only saintly miracles could avert their wrath. For this reason the relics of Saint Agatha were paraded in front of lava advancing on Catania in 253 A.D., and miraculously the lava clove in two (down two valleys) and spared the town. Unfortunately the relics of St. Agatha proved ineffective in 1669, with the loss of much of Catania to Etna's lava.
In 1660 the eruption of Vesuvius rained twinned pyroxene crystals and ash upon the nearby villages. The twinned pyroxene crystals resembled the crucifix and this was interpreted as the work of Saint Januarius. In Naples, the relics of St Januarius are paraded through town at every major eructation of Vesuvius. The register of these processions allowed British diplomat and amateur naturalist Sir William Hamilton to document Vesuvius' eruptions, one of the first few 'scientific' studies of the eruptive history of a volcano.
An aerial photo of Vesuvius
Renaissance observations
Renaissance descriptions of volcanoes vastly improved the state of knowledge, despite the resistance of the Church to scientific explorations of the natural world, especially those which were at odds with Biblical teachings. Nevertheless, nuées ardentes were described from the Azores in 1580. Georgius Agricola argued the rays of the sun, as later proposed by Descartes had nothing to do with volcanoes. Agricola believed vapor under pressure caused eruptions of 'mointain oil' and basalt.
Jesuit Athanasius Kircher (1602–1680) witnessed eruptions of Mount Etna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur, bitumen and coal.
Johannes Kepler considered volcanoes as conduits for the tears and excrement of the Earth, voiding bitumen, tar and sulfur. Descartes, pronouncing that God had created the Earth in an instant, declared he had done so in three layers; the fiery depths, a layer of water, and the air. Volcanoes, he said, were formed where the rays of the sun pierced the earth.
Science wrestled with the ideas of the combustion of pyrite with water, that rock was solidified bitumen, and with notions of rock being formed from water (Neptunism). Of the volcanoes then known, all were near the water, hence the action of the sea upon the land was used to explain volcanism.
Modern volcanology
Seismic observations are made using seismographs deployed near volcanic areas, watching out for increased seismicity during volcanic events, in particular looking for long period harmonic tremors which signal magma movement through volcanic conduits.[3]
Surface deformation monitoring includes the use of geodetic techniques such as leveling, tilt, strain, angle and distance measurements through tiltmeters, total stations and EDMs. This also includes GNSS observations and InSAR.[4][5] Surface deformation indicates magma upwelling: increased magma supply produces bulges in the volcanic center's surface.
Gas emissions may be monitored with equipment including portable ultra-violet spectrometers (COSPEC, now superseded by the miniDOAS) which analyzes the presence of volcanic gases such as sulfur dioxide; or by infra-red spectroscopy (FTIR). Increased gas emissions, and more particularly changes in gas compositions, may signal an impending volcanic eruption.
Temperature changes are monitored using thermometers and observing changes in thermal properties of volcanic lakes and vents which may indicate upcoming activity.
Other geophysical techniques (electrical, gravity and magnetic observations) include monitoring fluctuations and sudden change in resistivity, gravity anomalies or magnetic anomaly patterns which may indicate volcano-induced faulting and magma upwelling.
Stratigraphic analyses includes analyzing tephra and lava deposits and dating these to give volcano eruption patterns, with estimated cycles of intense activity and size of eruptions.
Volcanologist examining tephra horizons in south-central Iceland.
A volcanologist is a person who studies the formation of volcanoes, and their current and historic eruptions. Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions, collect eruptive products including tephra (such as ash or pumice), rock and lava samples. One major focus of enquiry is the prediction of eruptions; there is currently no accurate way to do this, but predicting eruptions, like predicting earthquakes, could save many lives.
History of volcanology
Volcanology has an extensive history. The earliest known recording of a volcanic eruption may be on a wall painting dated to about 7000 B.C.E. found at the Neolithic site at Çatal Höyük (now known as Çatalhöyük), in Anatolia, Turkey. This painting has been interpreted as a depiction of an erupting volcano, with a cluster of houses below shows a twin peaked volcano in eruption, with a town at its base (though archaeologists now question this interpretation [1]). The volcano may be either Hasan Dağ, or its smaller neighbour, Melendiz Dağ. [2]
[edit] Mythical explanations
The classical world of Greece and the early Roman Empire explained volcanoes as the work of the gods as science and alchemy had no explanation for their existence. Grecian myths and tales tell of Atlantis, a fabled island which sank into the sea. Plato (428-348 B.C.) told of the disappearance of a vast island and its powerful civilization, the Atlanteans, in two of his dialogues, Critias and Timaeus. It is now considered that the island of Thera, now Santorini, in the Aegean Sea, was destroyed by a tremendous series of volcanic explosions around 1620 B.C., with ash falls of up to a foot deep recorded in Turkey. The explosion of Thera sent colossal tsunamis, estimated at 100 feet height, racing across the Aegean, and the southern coast of Crete. Other recordings of the Thera eruption spawned Greek myths, namely the Deucalion, in which Poseidon, god of the sea, took revenge upon Zeus by inundating Attica, Argolis, Salonika, Rhodes and the coast of Lycia (Turkey) to Sicily.
Greeks also considered that Hephaestus, the god of fire, sat below the volcano Etna, forging the weapons of Zeus. His minions, the cyclops with their single staring eye, may be an allegory to the round craters and cones of a volcano. Indeed, the Greek word used to describe volcanoes was etna, or hiera, after Heracles, the son of Zeus. The Roman poet Virgil, in interpreting the Greek mythos, held that the hero Enceladus was buried beneath Etna by the goddess Athena as punishment for disobeying the gods; the mountain's rumblings were his tormented cries, the flames his breath and the tremors his railing against the bars of his prison. Enceladus' brother Mimas was buried beneath Vesuvius by Hephaestus, and the blood of other defeated giants welled up in the Phlegrean Fields surrounding Vesuvius.
Tribal legends of volcanoes abound from the Pacific Ring of Fire and the Americas, usually invoking the forces of the supernatural or the divine to explain the violent outbursts of volcanoes. Taranaki and Tongariro, according to Māori mythology, were lovers who fell in love with Pihanga, and a spiteful jealous fight ensued. Māori will not to this day live between Tongariro and Taranaki for fear of the dispute flaring up again.
Greco-Roman science
Eruption of Vesuvius in 1822. The eruption of AD 79 would have appeared very similar.
The first attempt at a scientific explanation of volcanoes was undertaken by the Greek philosopher Empedocles (c. 490-430 B.C.), who saw the world divided into four elemental forces, of Earth, Air, Fire and Water. Volcanoes, Empedocles maintained, were the manifestation of Elemental Fire. Plato contended that channels of hot and cold waters flow in inexhaustible quantities through subterranean rivers. In the depths of the earth snakes a vast river of fire, the Pyriphlegethon, which feeds all the world's volcanoes. Aristotle considered underground fire as the result of "the...friction of the wind when it plunges into narrow passages."
Wind would play a key role in explanations of volcanoes until the 16th century. Lucretius, a Roman philosopher, claimed Etna was completely hollow and the fires of the underground driven by a fierce wind circulating near sea level. Ovid believed that the flame was fed from "fatty foods" and eruptions stopped when the food ran out. Vitruvius contended that sulfur, alum and bitumen fed the deep fires. Observations by Pliny the Elder noted the presence of earthquakes preceded an eruption; he died in the eruption of Vesuvius in 79 AD while investigating it at Stabiae. His nephew, Pliny the Younger gave detailed descriptions of the eruption in which his uncle died, attributing his death to the effects of toxic gases. Such eruptions have been named Plinian in honour of the two authors.
Christian mythology
The study of volcanology was not advanced much between the days of Plato and Hutton. The Christian world explained volcanoes by a multitude of prescientific notions, but it was also thought they were the work of Satan or the wrath of God, and only saintly miracles could avert their wrath. For this reason the relics of Saint Agatha were paraded in front of lava advancing on Catania in 253 A.D., and miraculously the lava clove in two (down two valleys) and spared the town. Unfortunately the relics of St. Agatha proved ineffective in 1669, with the loss of much of Catania to Etna's lava.
In 1660 the eruption of Vesuvius rained twinned pyroxene crystals and ash upon the nearby villages. The twinned pyroxene crystals resembled the crucifix and this was interpreted as the work of Saint Januarius. In Naples, the relics of St Januarius are paraded through town at every major eructation of Vesuvius. The register of these processions allowed British diplomat and amateur naturalist Sir William Hamilton to document Vesuvius' eruptions, one of the first few 'scientific' studies of the eruptive history of a volcano.
An aerial photo of Vesuvius
Renaissance observations
Renaissance descriptions of volcanoes vastly improved the state of knowledge, despite the resistance of the Church to scientific explorations of the natural world, especially those which were at odds with Biblical teachings. Nevertheless, nuées ardentes were described from the Azores in 1580. Georgius Agricola argued the rays of the sun, as later proposed by Descartes had nothing to do with volcanoes. Agricola believed vapor under pressure caused eruptions of 'mointain oil' and basalt.
Jesuit Athanasius Kircher (1602–1680) witnessed eruptions of Mount Etna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur, bitumen and coal.
Johannes Kepler considered volcanoes as conduits for the tears and excrement of the Earth, voiding bitumen, tar and sulfur. Descartes, pronouncing that God had created the Earth in an instant, declared he had done so in three layers; the fiery depths, a layer of water, and the air. Volcanoes, he said, were formed where the rays of the sun pierced the earth.
Science wrestled with the ideas of the combustion of pyrite with water, that rock was solidified bitumen, and with notions of rock being formed from water (Neptunism). Of the volcanoes then known, all were near the water, hence the action of the sea upon the land was used to explain volcanism.
Modern volcanology
Seismic observations are made using seismographs deployed near volcanic areas, watching out for increased seismicity during volcanic events, in particular looking for long period harmonic tremors which signal magma movement through volcanic conduits.[3]
Surface deformation monitoring includes the use of geodetic techniques such as leveling, tilt, strain, angle and distance measurements through tiltmeters, total stations and EDMs. This also includes GNSS observations and InSAR.[4][5] Surface deformation indicates magma upwelling: increased magma supply produces bulges in the volcanic center's surface.
Gas emissions may be monitored with equipment including portable ultra-violet spectrometers (COSPEC, now superseded by the miniDOAS) which analyzes the presence of volcanic gases such as sulfur dioxide; or by infra-red spectroscopy (FTIR). Increased gas emissions, and more particularly changes in gas compositions, may signal an impending volcanic eruption.
Temperature changes are monitored using thermometers and observing changes in thermal properties of volcanic lakes and vents which may indicate upcoming activity.
Other geophysical techniques (electrical, gravity and magnetic observations) include monitoring fluctuations and sudden change in resistivity, gravity anomalies or magnetic anomaly patterns which may indicate volcano-induced faulting and magma upwelling.
Stratigraphic analyses includes analyzing tephra and lava deposits and dating these to give volcano eruption patterns, with estimated cycles of intense activity and size of eruptions.
Glaciology
laciology (from Middle French dialect (Franco-Provençal): glace, "ice"; or Latin: glacies, "frost, ice"; and Greek: λόγος, logos, "speech" lit. "study of ice") is the study of glaciers, or more generally ice and natural phenomena that involve ice.
Glaciology is an interdisciplinary earth science that integrates geophysics, geology, physical geography, geomorphology, climatology, meteorology, hydrology, biology, and ecology. The impact of glaciers on humans adds the fields of human geography and anthropology. The presence of ice on Mars and Europa brings in an extraterrestrial component to the field.
Overview
Areas of study within glaciology include glacial history and the reconstruction of past glaciation. A glaciologist is a person who studies glaciers. Glaciology is one of the key areas of polar research. A glacier is an extended mass of ice formed from snow falling and accumulating over the years and moving very slowly, either descending from high mountains, as in valley glaciers, or moving outward from centers of accumulation, as in continental glaciers.
[edit] Types
There are two general categories of glaciation which glaciologists distinguish: alpine glaciation, accumulations or "rivers of ice" confined to valleys; and continental glaciation, unrestricted accumulations which once covered much of the northern continents.
* Alpine - ice flows down the valleys of mountainous areas and forms a tongue of ice moving towards the plains below. Alpine glaciers tend to make the topography more rugged, by adding and improving the scale of existing features such as large ravines called cirques and ridges where the rims of two cirques meet called arêtes.
* Continental - an ice sheet found today, only in high latitudes (Greenland/Antarctica), thousands of square kilometers in area and thousands of meters thick. These tend to smooth out the landscapes.
Zones of glaciers
* Accumulation, where the formation of ice is faster than its removal.
* Wastage or Ablation, where the sum of melting and evaporation (sublimation) is greater than the amount of snow added each year.
Movement
Ablation
wastage of the glacier through sublimation, ice melting and iceberg calving.
Ablation zone
Area of a glacier in which the annual loss of ice through ablation exceeds the annual gain from precipitation.
Arête
an acute ridge of rock where two cirques abut.
Bergshrund
crevasse formed near the head of a glacier, where the mass of ice has rotated, sheared and torn itself apart in the manner of a geological fault.
Cirque, corrie or cwm
bowl shaped depression excavated by the source of a glacier.
Creep
adjustment to stress at a molecular level.
Flow
movement (of ice) in a constant direction.
Fracture
brittle failure (breaking of ice) under the stress raised when movement is too rapid to be accommodated by creep. It happens for example, as the central part of a glacier movinges faster than the edges.
Horn
spire of rock formed by the headward erosion of a ring of cirques around a single mountain. It is an extreme case of an arête.
Plucking/Quarrying
where the adhesion of the ice to the rock is stronger than the cohesion of the rock, part of the rock leaves with the flowing ice.
Tarn
a lake formed in the bottom of a cirque when its glacier has melted.
Tunnel valley
The tunnel is that formed by hydraulic erosion of ice and rock below an ice sheet margin. The tunnel valley is what remains of it in the underlying rock when the ice sheet has melted.
Glacial deposits
Stratified
Outwash sand/gravel
from front of glaciers, found on a plain
Kettles
block of stagnant ice leaves a depression or pit
Eskers
steep sided ridges of gravel/sand, possibly caused by streams running under stagnant ice
Kames
stratified drift builds up low steep hills
Varves
alternating thin sedimentary beds (coarse and fine) of a proglacial lake. Summer conditions deposit more and coarser material and those of the winter, less and finer.
Unstratified
Till-unsorted
(glacial flour to boulders) deposited by receding/advancing glaciers, forming moraines, and drumlins
Moraines
(Terminal) material deposited at the end; (Ground) material deposited as glacier melts; (lateral) material deposited along the sides.
Drumlins
smooth elongated hills composed of till.
Ribbed moraines
large subglacial elongated hills transverse to former ice flow.
Glaciology is an interdisciplinary earth science that integrates geophysics, geology, physical geography, geomorphology, climatology, meteorology, hydrology, biology, and ecology. The impact of glaciers on humans adds the fields of human geography and anthropology. The presence of ice on Mars and Europa brings in an extraterrestrial component to the field.
Overview
Areas of study within glaciology include glacial history and the reconstruction of past glaciation. A glaciologist is a person who studies glaciers. Glaciology is one of the key areas of polar research. A glacier is an extended mass of ice formed from snow falling and accumulating over the years and moving very slowly, either descending from high mountains, as in valley glaciers, or moving outward from centers of accumulation, as in continental glaciers.
[edit] Types
There are two general categories of glaciation which glaciologists distinguish: alpine glaciation, accumulations or "rivers of ice" confined to valleys; and continental glaciation, unrestricted accumulations which once covered much of the northern continents.
* Alpine - ice flows down the valleys of mountainous areas and forms a tongue of ice moving towards the plains below. Alpine glaciers tend to make the topography more rugged, by adding and improving the scale of existing features such as large ravines called cirques and ridges where the rims of two cirques meet called arêtes.
* Continental - an ice sheet found today, only in high latitudes (Greenland/Antarctica), thousands of square kilometers in area and thousands of meters thick. These tend to smooth out the landscapes.
Zones of glaciers
* Accumulation, where the formation of ice is faster than its removal.
* Wastage or Ablation, where the sum of melting and evaporation (sublimation) is greater than the amount of snow added each year.
Movement
Ablation
wastage of the glacier through sublimation, ice melting and iceberg calving.
Ablation zone
Area of a glacier in which the annual loss of ice through ablation exceeds the annual gain from precipitation.
Arête
an acute ridge of rock where two cirques abut.
Bergshrund
crevasse formed near the head of a glacier, where the mass of ice has rotated, sheared and torn itself apart in the manner of a geological fault.
Cirque, corrie or cwm
bowl shaped depression excavated by the source of a glacier.
Creep
adjustment to stress at a molecular level.
Flow
movement (of ice) in a constant direction.
Fracture
brittle failure (breaking of ice) under the stress raised when movement is too rapid to be accommodated by creep. It happens for example, as the central part of a glacier movinges faster than the edges.
Horn
spire of rock formed by the headward erosion of a ring of cirques around a single mountain. It is an extreme case of an arête.
Plucking/Quarrying
where the adhesion of the ice to the rock is stronger than the cohesion of the rock, part of the rock leaves with the flowing ice.
Tarn
a lake formed in the bottom of a cirque when its glacier has melted.
Tunnel valley
The tunnel is that formed by hydraulic erosion of ice and rock below an ice sheet margin. The tunnel valley is what remains of it in the underlying rock when the ice sheet has melted.
Glacial deposits
Stratified
Outwash sand/gravel
from front of glaciers, found on a plain
Kettles
block of stagnant ice leaves a depression or pit
Eskers
steep sided ridges of gravel/sand, possibly caused by streams running under stagnant ice
Kames
stratified drift builds up low steep hills
Varves
alternating thin sedimentary beds (coarse and fine) of a proglacial lake. Summer conditions deposit more and coarser material and those of the winter, less and finer.
Unstratified
Till-unsorted
(glacial flour to boulders) deposited by receding/advancing glaciers, forming moraines, and drumlins
Moraines
(Terminal) material deposited at the end; (Ground) material deposited as glacier melts; (lateral) material deposited along the sides.
Drumlins
smooth elongated hills composed of till.
Ribbed moraines
large subglacial elongated hills transverse to former ice flow.
Monday, March 15, 2010
Seismology
Seismology (from Greek σεισμός, seismos, "earthquake"; and -λόγος, -logia, as a whole "Talking about earthquakes") is the scientific study of earthquakes and the propagation of elastic waves through the Earth. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes (such as explosions). A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of earth motion as a function of time is called a seismogram.
Seismic waves
Main article: Seismic wave
Earthquakes, and other sources, produce different types of seismic waves which travel through rock, and provide an effective way to image both sources and structures deep within the Earth. There are three basic types of seismic waves in solids: P-waves, S-waves (both body waves) and interface waves. The two basic kinds of surface waves (Rayleigh and Love) which travel along a solid-air interface, can be fundamentally explained in terms of interacting P- and/or S-waves.
Propagation of seismic wave in the ground and the effect of presence of land mine.
Pressure waves or Primary waves (P-waves), are longitudinal waves that travel at maximum velocity within solids and are therefore the first waves to appear on a seismogram.
S-waves, also called shear or secondary waves, are transverse waves that travel more slowly than P-waves and thus appear later than P-waves on a seismogram. Particle motion is perpendicular to the direction of wave propagation. Shear waves do not exist in fluids with essentially no shear strength, such as air or water.
Surface waves travel more slowly than P-waves and S-waves, but because they are guided by the surface of the Earth (and their energy is thus trapped near the Earth's surface) they can be much larger in amplitude than body waves, and can be the largest signals seen in earthquake seismograms. They are particularly strongly excited when the seismic source is close to the surface of the Earth, such as the case of a shallow earthquake or explosion.
For large enough earthquakes, one can observe the normal modes of the Earth. These modes are excited as discrete frequencies and can be observed for days after the generating event. The first observations were made in the 1960s as the advent of higher fidelity instruments coincided with two of the largest earthquakes of the 20th century - the 1960 Great Chilean earthquake and the 1964 Great Alaskan earthquake. Since then, the normal modes of the Earth have given us some of the strongest constraints on the deep structure of the Earth.
One of the earliest important discoveries (suggested by Richard Dixon Oldham in 1906 and definitively shown by Harold Jeffreys in 1926) was that the outer core of the Earth is liquid. Pressure waves (P-waves) pass through the core. Transverse or shear waves (S-waves) that shake side-to-side require rigid material so they do not pass through the outer core. Thus, the liquid core causes a "shadow" on the side of the planet opposite of the earthquake where no direct S-waves are observed. The reduction in P-wave velocity of the outer core also causes a substantial delay for P waves penetrating the core from the (seismically faster velocity) mantle.
Seismic waves produced by explosions or vibrating controlled sources are one of the primary methods of underground exploration in geophysics (in addition to many different electromagnetic methods such as induced polarization and magnetotellurics). Controlled source seismology has been used to map salt domes, faults, anticlines and other geologic traps in petroleum-bearing rocks, geological faults, rock types, and long-buried giant meteor craters. For example, the Chicxulub impactor, which is believed to have killed the dinosaurs, was localized to Central America by analyzing ejecta in the cretaceous boundary, and then physically proven to exist using seismic maps from oil exploration.
Using seismic tomography with earthquake waves, the interior of the Earth has been completely mapped to a resolution of several hundred kilometers. This process has enabled scientists to identify convection cells, mantle plumes and other large-scale features of the inner Earth.
Seismographs are instruments that sense and record the motion of the Earth. Networks of seismographs today continuously monitor the seismic environment of the planet, allowing for the monitoring and analysis of global earthquakes and tsunami warnings, as well as recording a variety of seismic signals arising from non-earthquake sources ranging from explosions (nuclear and chemical), to pressure variations on the ocean floor induced by ocean waves (the global microseism), to cryospheric events associated with large icebergs and glaciers. Above-ocean meteor strikes as large as ten kilotons of TNT, (equivalent to about 4.2 × 1013 J of effective explosive force) have been recorded by seismographs. A major motivation for the global instrumentation of the Earth with seismographs has been for the monitoring of nuclear testing.
One of the first attempts at the scientific study of earthquakes followed the 1755 Lisbon earthquake. Other especially notable earthquakes that spurred major developments in the science of seismology include the 1857 Basilicata earthquake, 1906 San Francisco earthquake, the 1964 Alaska earthquake and the 2004 Sumatra-Andaman earthquake. An extensive list of famous earthquakes can be found on the List of earthquakes page.
[edit] Earthquake prediction
Main article: Earthquake prediction
Forecasting a probable timing, location, magnitude and other important features of a forthcoming seismic event is called earthquake prediction. Most seismologists do not believe that a system to provide timely warnings for individual earthquakes has yet been developed, and many believe that such a system would be unlikely to give significant warning of impending seismic events. More general forecasts, however, are routinely used to establish seismic hazard. Such forecasts estimate the probability of an earthquake of a particular size affecting a particular location within a particular time span and they are routinely used in earthquake engineering.
Various attempts have been made by seismologists and others to create effective systems for precise earthquake predictions, including the VAN method. Such methods have yet to be generally accepted in the seismology community.
Seismic waves
Main article: Seismic wave
Earthquakes, and other sources, produce different types of seismic waves which travel through rock, and provide an effective way to image both sources and structures deep within the Earth. There are three basic types of seismic waves in solids: P-waves, S-waves (both body waves) and interface waves. The two basic kinds of surface waves (Rayleigh and Love) which travel along a solid-air interface, can be fundamentally explained in terms of interacting P- and/or S-waves.
Propagation of seismic wave in the ground and the effect of presence of land mine.
Pressure waves or Primary waves (P-waves), are longitudinal waves that travel at maximum velocity within solids and are therefore the first waves to appear on a seismogram.
S-waves, also called shear or secondary waves, are transverse waves that travel more slowly than P-waves and thus appear later than P-waves on a seismogram. Particle motion is perpendicular to the direction of wave propagation. Shear waves do not exist in fluids with essentially no shear strength, such as air or water.
Surface waves travel more slowly than P-waves and S-waves, but because they are guided by the surface of the Earth (and their energy is thus trapped near the Earth's surface) they can be much larger in amplitude than body waves, and can be the largest signals seen in earthquake seismograms. They are particularly strongly excited when the seismic source is close to the surface of the Earth, such as the case of a shallow earthquake or explosion.
For large enough earthquakes, one can observe the normal modes of the Earth. These modes are excited as discrete frequencies and can be observed for days after the generating event. The first observations were made in the 1960s as the advent of higher fidelity instruments coincided with two of the largest earthquakes of the 20th century - the 1960 Great Chilean earthquake and the 1964 Great Alaskan earthquake. Since then, the normal modes of the Earth have given us some of the strongest constraints on the deep structure of the Earth.
One of the earliest important discoveries (suggested by Richard Dixon Oldham in 1906 and definitively shown by Harold Jeffreys in 1926) was that the outer core of the Earth is liquid. Pressure waves (P-waves) pass through the core. Transverse or shear waves (S-waves) that shake side-to-side require rigid material so they do not pass through the outer core. Thus, the liquid core causes a "shadow" on the side of the planet opposite of the earthquake where no direct S-waves are observed. The reduction in P-wave velocity of the outer core also causes a substantial delay for P waves penetrating the core from the (seismically faster velocity) mantle.
Seismic waves produced by explosions or vibrating controlled sources are one of the primary methods of underground exploration in geophysics (in addition to many different electromagnetic methods such as induced polarization and magnetotellurics). Controlled source seismology has been used to map salt domes, faults, anticlines and other geologic traps in petroleum-bearing rocks, geological faults, rock types, and long-buried giant meteor craters. For example, the Chicxulub impactor, which is believed to have killed the dinosaurs, was localized to Central America by analyzing ejecta in the cretaceous boundary, and then physically proven to exist using seismic maps from oil exploration.
Using seismic tomography with earthquake waves, the interior of the Earth has been completely mapped to a resolution of several hundred kilometers. This process has enabled scientists to identify convection cells, mantle plumes and other large-scale features of the inner Earth.
Seismographs are instruments that sense and record the motion of the Earth. Networks of seismographs today continuously monitor the seismic environment of the planet, allowing for the monitoring and analysis of global earthquakes and tsunami warnings, as well as recording a variety of seismic signals arising from non-earthquake sources ranging from explosions (nuclear and chemical), to pressure variations on the ocean floor induced by ocean waves (the global microseism), to cryospheric events associated with large icebergs and glaciers. Above-ocean meteor strikes as large as ten kilotons of TNT, (equivalent to about 4.2 × 1013 J of effective explosive force) have been recorded by seismographs. A major motivation for the global instrumentation of the Earth with seismographs has been for the monitoring of nuclear testing.
One of the first attempts at the scientific study of earthquakes followed the 1755 Lisbon earthquake. Other especially notable earthquakes that spurred major developments in the science of seismology include the 1857 Basilicata earthquake, 1906 San Francisco earthquake, the 1964 Alaska earthquake and the 2004 Sumatra-Andaman earthquake. An extensive list of famous earthquakes can be found on the List of earthquakes page.
[edit] Earthquake prediction
Main article: Earthquake prediction
Forecasting a probable timing, location, magnitude and other important features of a forthcoming seismic event is called earthquake prediction. Most seismologists do not believe that a system to provide timely warnings for individual earthquakes has yet been developed, and many believe that such a system would be unlikely to give significant warning of impending seismic events. More general forecasts, however, are routinely used to establish seismic hazard. Such forecasts estimate the probability of an earthquake of a particular size affecting a particular location within a particular time span and they are routinely used in earthquake engineering.
Various attempts have been made by seismologists and others to create effective systems for precise earthquake predictions, including the VAN method. Such methods have yet to be generally accepted in the seismology community.
Hydrogeology
Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust, (commonly in aquifers). The term geohydrology is often used interchangeably. Some make the minor distinction between a hydrologist or engineer applying themselves to geology (geohydrology), and a geologist applying themselves to hydrology (hydrogeology).
Introduction
Hydrogeology is an interdisciplinary subject; it can be difficult to account fully for the chemical, physical, biological and even legal interactions between soil, water, nature and society. The study of the interaction between groundwater movement and geology can be quite complex. Groundwater does not always flow in the subsurface down-hill following the surface topography; groundwater follows pressure gradients (flow from high pressure to low) often following fractures and conduits in circuitous paths. Taking into account the interplay of the different facets of a multi-component system often requires knowledge in several diverse fields at both the experimental and theoretical levels. This being said, the following is a more traditional introduction to the methods and nomenclature of saturated subsurface hydrology, or simply hydrogeology.
[edit] Hydrogeology in relation to other fields
Hydrogeology, as stated above, is a branch of the earth sciences dealing with the flow of water through aquifers and other shallow porous media (typically less than 450 m or 1,500 ft below the land surface.) The very shallow flow of water in the subsurface (the upper 3 m or 10 ft) is pertinent to the fields of soil science, agriculture and civil engineering, as well as to hydrogeology. The general flow of fluids (water, hydrocarbons, geothermal fluids, etc.) in deeper formations is also a concern of geologists, geophysicists and petroleum geologists. Groundwater is a slow-moving, viscous fluid (with a Reynolds number less than unity); many of the empirically derived laws of groundwater flow can be alternately derived in fluid mechanics from the special case of Stokes flow (viscosity and pressure terms, but no inertial term).
The mathematical relationships used to describe the flow of water through porous media are the diffusion and Laplace equations, which have applications in many diverse fields. Steady groundwater flow (Laplace equation) has been simulated using electrical, elastic and heat conduction analogies. Transient groundwater flow is analogous to the diffusion of heat in a solid, therefore some solutions to hydrological problems have been adapted from heat transfer literature.
Traditionally, the movement of groundwater has been studied separately from surface water, climatology, and even the chemical and microbiological aspects of hydrogeology (the processes are uncoupled). As the field of hydrogeology matures, the strong interactions between groundwater, surface water, water chemistry, soil moisture and even climate are becoming more clear.
[edit] Definitions and material properties
Main article: Aquifer
One of the main tasks a hydrogeologist typically performs is the prediction of future behavior of an aquifer system, based on analysis of past and present observations. Some hypothetical, but characteristic questions asked would be:
* Can the aquifer support another subdivision?
* Will the river dry up if the farmer doubles his irrigation?
* Did the chemicals from the dry cleaning facility travel through the aquifer to my well and make me sick?
* Will the plume of effluent leaving my neighbor's septic system flow to my drinking water well?
Most of these questions can be addressed through simulation of the hydrologic system (using numerical models or analytic equations). Accurate simulation of the aquifer system requires knowledge of the aquifer properties and boundary conditions. Therefore a common task of the hydrogeologist is determining aquifer properties using aquifer tests.
In order to further characterize aquifers and aquitards some primary and derived physical properties are introduced below. Aquifers are broadly classified as being either confined or unconfined (water table aquifers), and either saturated or unsaturated; the type of aquifer affects what properties control the flow of water in that medium (e.g., the release of water from storage for confined aquifers is related to the storativity, while it is related to the specific yield for unconfined aquifers).
[edit] Hydraulic head
Main article: Hydraulic head
Changes in hydraulic head (h) are the driving force which causes water to move from one place to another. It is composed of pressure head (ψ) and elevation head (z). The head gradient is the change in hydraulic head per length of flowpath, and appears in Darcy's law as being proportional to the discharge.
Hydraulic head is a directly measurable property that can take on any value (because of the arbitrary datum involved in the z term); ψ can be measured with a pressure transducer (this value can be negative, e.g., suction, but is positive in saturated aquifers), and z can be measured relative to a surveyed datum (typically the top of the well casing). Commonly, in wells tapping unconfined aquifers the water level in a well is used as a proxy for hydraulic head, assuming there is no vertical gradient of pressure. Often only changes in hydraulic head through time are needed, so the constant elevation head term can be left out (Δh = Δψ).
A record of hydraulic head through time at a well is a hydrograph or, the changes in hydraulic head recorded during the pumping of a well in a test are called drawdown.
[edit] Porosity
Main article: Porosity
Porosity (n) is a directly measurable aquifer property; it is a fraction between 0 and 1 indicating the amount of pore space between unconsolidated soil particles or within a fractured rock. Typically, the majority of groundwater (and anything dissolved in it) moves through the porosity available to flow (sometimes called effective porosity). Permeability is an expression of the connectedness of the pores. For instance, an unfractured rock unit may have a high porosity (it has lots of holes between its constituent grains), but a low permeability (none of the pores are connected). An example of this phenomenon is pumice, which, when in its unfractured state, can make a poor aquifer.
Porosity does not directly affect the distribution of hydraulic head in an aquifer, but it has a very strong effect on the migration of dissolved contaminants, since it affects groundwater flow velocities through an inversely proportional relationship.
[edit] Water content
Main article: water content
Water content (θ) is also a directly measurable property; it is the fraction of the total rock which is filled with liquid water. This is also a fraction between 0 and 1, but it must also be less than or equal to the total porosity.
The water content is very important in vadose zone hydrology, where the hydraulic conductivity is a strongly nonlinear function of water content; this complicates the solution of the unsaturated groundwater flow equation.
[edit] Hydraulic conductivity
Main article: Hydraulic conductivity
Hydraulic conductivity (K) and transmissivity (T) are indirect aquifer properties (they cannot be measured directly). T is the K integrated over the vertical thickness (b) of the aquifer (T=Kb when K is constant over the entire thickness). These properties are measures of an aquifer's ability to transmit water. Intrinsic permeability (κ) is a secondary medium property which does not depend on the viscosity and density of the fluid (K and T are specific to water); it is used more in the petroleum industry.
[edit] Specific storage and specific yield
Main article: Specific storage
Specific storage (Ss) and its depth-integrated equivalent, storativity (S=Ssb), are indirect aquifer properties (they cannot be measured directly); they indicate the amount of groundwater released from storage due to a unit depressurization of a confined aquifer. They are fractions between 0 and 1.
Specific yield (Sy) is also a ratio between 0 and 1 (Sy ≤ porosity) and indicates the amount of water released due to drainage from lowering the water table in an unconfined aquifer. Typically Sy is orders of magnitude larger than Ss. Often the porosity or effective porosity is used as an upper bound to the specific yield.
[edit] Contaminant transport properties
Often we are interested in how the moving groundwater water will move dissolved contaminants around (the sub-field of contaminant hydrogeology). The contaminants can be man-made (e.g., petroleum products, nitrate or Chromium) or naturally occurring (e.g., arsenic, salinity). Besides needing to understand where the groundwater is flowing, based on the other hydrologic properties discussed above, there are additional aquifer properties which affect how dissolved contaminants move with groundwater.
Dispersivity (αL, αT) is an empirical factor which quantifies how much contaminants stray away from the path of the groundwater which is carrying it. Some of the contaminants will be "behind" or "ahead" the mean groundwater, giving rise to a longitudinal dispersivity (αL), and some will be "to the sides of" the pure advective groundwater flow, leading to a transverse dispersivity (αT).
Dispersivity is actually a factor which represents our lack of information about the system we are simulating. There are many small details about the aquifer which are being averaged when using a macroscopic approach (e.g., tiny beds of gravel and clay in sand aquifers), they manifest themselves as an apparent dispersivity. Because of this, α is often claimed to be dependent on the length scale of the problem — the dispersivity found for transport through 1 m³ of aquifer is different than that for transport through 1 cm³ of the same aquifer material.
Hydrodynamic dispersion (D) is a positive physical parameter which describes the molecule-scale movement of solute away from the mean flow; it is a result of Brownian motion. This is the same mechanism as dye uniformly spreading out in a still bucket of water. The dispersion coefficient is typically quite small (typically orders of magnitude smaller than α), and can often be considered negligible (unless groundwater flow velocities are extremely low, as they are in clay aquitards).
It is important not to confuse hydrodynamic dispersion with dispersivity, as the former is a physical phenomenon and the latter is an empirical factor which is cast into a similar form as dispersion, because we already know how to solve that problem.
[edit] Governing equations
[edit] Darcy's Law
Main article: Darcy's law
Darcy's law is a Constitutive equation (empirically derived by Henri Darcy, in 1856) that states the amount of groundwater discharging through a given portion of aquifer is proportional to the cross-sectional area of flow, the hydraulic head gradient, and the hydraulic conductivity.
[edit] Groundwater flow equation
Main article: Groundwater flow equation
The groundwater flow equation, in its most general form, describes the movement of groundwater in a porous medium (aquifers and aquitards). It is known in mathematics as the diffusion equation, and has many analogs in other fields. Many solutions for groundwater flow problems were borrowed or adapted from existing heat transfer solutions.
It is often derived from a physical basis using Darcy's law and a conservation of mass for a small control volume. The equation is often used to predict flow to wells, which have radial symmetry, so the flow equation is commonly solved in polar or cylindrical coordinates.
The Theis equation is one of the most commonly used and fundamental solutions to the groundwater flow equation; it can be used to predict the transient evolution of head due to the effects of pumping one or a number of pumping wells.
The Thiem equation is a solution to the steady state groundwater flow equation (Laplace's Equation). Unless there are large sources of water nearby (a river or lake), true steady-state is rarely achieved in reality.
Introduction
Hydrogeology is an interdisciplinary subject; it can be difficult to account fully for the chemical, physical, biological and even legal interactions between soil, water, nature and society. The study of the interaction between groundwater movement and geology can be quite complex. Groundwater does not always flow in the subsurface down-hill following the surface topography; groundwater follows pressure gradients (flow from high pressure to low) often following fractures and conduits in circuitous paths. Taking into account the interplay of the different facets of a multi-component system often requires knowledge in several diverse fields at both the experimental and theoretical levels. This being said, the following is a more traditional introduction to the methods and nomenclature of saturated subsurface hydrology, or simply hydrogeology.
[edit] Hydrogeology in relation to other fields
Hydrogeology, as stated above, is a branch of the earth sciences dealing with the flow of water through aquifers and other shallow porous media (typically less than 450 m or 1,500 ft below the land surface.) The very shallow flow of water in the subsurface (the upper 3 m or 10 ft) is pertinent to the fields of soil science, agriculture and civil engineering, as well as to hydrogeology. The general flow of fluids (water, hydrocarbons, geothermal fluids, etc.) in deeper formations is also a concern of geologists, geophysicists and petroleum geologists. Groundwater is a slow-moving, viscous fluid (with a Reynolds number less than unity); many of the empirically derived laws of groundwater flow can be alternately derived in fluid mechanics from the special case of Stokes flow (viscosity and pressure terms, but no inertial term).
The mathematical relationships used to describe the flow of water through porous media are the diffusion and Laplace equations, which have applications in many diverse fields. Steady groundwater flow (Laplace equation) has been simulated using electrical, elastic and heat conduction analogies. Transient groundwater flow is analogous to the diffusion of heat in a solid, therefore some solutions to hydrological problems have been adapted from heat transfer literature.
Traditionally, the movement of groundwater has been studied separately from surface water, climatology, and even the chemical and microbiological aspects of hydrogeology (the processes are uncoupled). As the field of hydrogeology matures, the strong interactions between groundwater, surface water, water chemistry, soil moisture and even climate are becoming more clear.
[edit] Definitions and material properties
Main article: Aquifer
One of the main tasks a hydrogeologist typically performs is the prediction of future behavior of an aquifer system, based on analysis of past and present observations. Some hypothetical, but characteristic questions asked would be:
* Can the aquifer support another subdivision?
* Will the river dry up if the farmer doubles his irrigation?
* Did the chemicals from the dry cleaning facility travel through the aquifer to my well and make me sick?
* Will the plume of effluent leaving my neighbor's septic system flow to my drinking water well?
Most of these questions can be addressed through simulation of the hydrologic system (using numerical models or analytic equations). Accurate simulation of the aquifer system requires knowledge of the aquifer properties and boundary conditions. Therefore a common task of the hydrogeologist is determining aquifer properties using aquifer tests.
In order to further characterize aquifers and aquitards some primary and derived physical properties are introduced below. Aquifers are broadly classified as being either confined or unconfined (water table aquifers), and either saturated or unsaturated; the type of aquifer affects what properties control the flow of water in that medium (e.g., the release of water from storage for confined aquifers is related to the storativity, while it is related to the specific yield for unconfined aquifers).
[edit] Hydraulic head
Main article: Hydraulic head
Changes in hydraulic head (h) are the driving force which causes water to move from one place to another. It is composed of pressure head (ψ) and elevation head (z). The head gradient is the change in hydraulic head per length of flowpath, and appears in Darcy's law as being proportional to the discharge.
Hydraulic head is a directly measurable property that can take on any value (because of the arbitrary datum involved in the z term); ψ can be measured with a pressure transducer (this value can be negative, e.g., suction, but is positive in saturated aquifers), and z can be measured relative to a surveyed datum (typically the top of the well casing). Commonly, in wells tapping unconfined aquifers the water level in a well is used as a proxy for hydraulic head, assuming there is no vertical gradient of pressure. Often only changes in hydraulic head through time are needed, so the constant elevation head term can be left out (Δh = Δψ).
A record of hydraulic head through time at a well is a hydrograph or, the changes in hydraulic head recorded during the pumping of a well in a test are called drawdown.
[edit] Porosity
Main article: Porosity
Porosity (n) is a directly measurable aquifer property; it is a fraction between 0 and 1 indicating the amount of pore space between unconsolidated soil particles or within a fractured rock. Typically, the majority of groundwater (and anything dissolved in it) moves through the porosity available to flow (sometimes called effective porosity). Permeability is an expression of the connectedness of the pores. For instance, an unfractured rock unit may have a high porosity (it has lots of holes between its constituent grains), but a low permeability (none of the pores are connected). An example of this phenomenon is pumice, which, when in its unfractured state, can make a poor aquifer.
Porosity does not directly affect the distribution of hydraulic head in an aquifer, but it has a very strong effect on the migration of dissolved contaminants, since it affects groundwater flow velocities through an inversely proportional relationship.
[edit] Water content
Main article: water content
Water content (θ) is also a directly measurable property; it is the fraction of the total rock which is filled with liquid water. This is also a fraction between 0 and 1, but it must also be less than or equal to the total porosity.
The water content is very important in vadose zone hydrology, where the hydraulic conductivity is a strongly nonlinear function of water content; this complicates the solution of the unsaturated groundwater flow equation.
[edit] Hydraulic conductivity
Main article: Hydraulic conductivity
Hydraulic conductivity (K) and transmissivity (T) are indirect aquifer properties (they cannot be measured directly). T is the K integrated over the vertical thickness (b) of the aquifer (T=Kb when K is constant over the entire thickness). These properties are measures of an aquifer's ability to transmit water. Intrinsic permeability (κ) is a secondary medium property which does not depend on the viscosity and density of the fluid (K and T are specific to water); it is used more in the petroleum industry.
[edit] Specific storage and specific yield
Main article: Specific storage
Specific storage (Ss) and its depth-integrated equivalent, storativity (S=Ssb), are indirect aquifer properties (they cannot be measured directly); they indicate the amount of groundwater released from storage due to a unit depressurization of a confined aquifer. They are fractions between 0 and 1.
Specific yield (Sy) is also a ratio between 0 and 1 (Sy ≤ porosity) and indicates the amount of water released due to drainage from lowering the water table in an unconfined aquifer. Typically Sy is orders of magnitude larger than Ss. Often the porosity or effective porosity is used as an upper bound to the specific yield.
[edit] Contaminant transport properties
Often we are interested in how the moving groundwater water will move dissolved contaminants around (the sub-field of contaminant hydrogeology). The contaminants can be man-made (e.g., petroleum products, nitrate or Chromium) or naturally occurring (e.g., arsenic, salinity). Besides needing to understand where the groundwater is flowing, based on the other hydrologic properties discussed above, there are additional aquifer properties which affect how dissolved contaminants move with groundwater.
Dispersivity (αL, αT) is an empirical factor which quantifies how much contaminants stray away from the path of the groundwater which is carrying it. Some of the contaminants will be "behind" or "ahead" the mean groundwater, giving rise to a longitudinal dispersivity (αL), and some will be "to the sides of" the pure advective groundwater flow, leading to a transverse dispersivity (αT).
Dispersivity is actually a factor which represents our lack of information about the system we are simulating. There are many small details about the aquifer which are being averaged when using a macroscopic approach (e.g., tiny beds of gravel and clay in sand aquifers), they manifest themselves as an apparent dispersivity. Because of this, α is often claimed to be dependent on the length scale of the problem — the dispersivity found for transport through 1 m³ of aquifer is different than that for transport through 1 cm³ of the same aquifer material.
Hydrodynamic dispersion (D) is a positive physical parameter which describes the molecule-scale movement of solute away from the mean flow; it is a result of Brownian motion. This is the same mechanism as dye uniformly spreading out in a still bucket of water. The dispersion coefficient is typically quite small (typically orders of magnitude smaller than α), and can often be considered negligible (unless groundwater flow velocities are extremely low, as they are in clay aquitards).
It is important not to confuse hydrodynamic dispersion with dispersivity, as the former is a physical phenomenon and the latter is an empirical factor which is cast into a similar form as dispersion, because we already know how to solve that problem.
[edit] Governing equations
[edit] Darcy's Law
Main article: Darcy's law
Darcy's law is a Constitutive equation (empirically derived by Henri Darcy, in 1856) that states the amount of groundwater discharging through a given portion of aquifer is proportional to the cross-sectional area of flow, the hydraulic head gradient, and the hydraulic conductivity.
[edit] Groundwater flow equation
Main article: Groundwater flow equation
The groundwater flow equation, in its most general form, describes the movement of groundwater in a porous medium (aquifers and aquitards). It is known in mathematics as the diffusion equation, and has many analogs in other fields. Many solutions for groundwater flow problems were borrowed or adapted from existing heat transfer solutions.
It is often derived from a physical basis using Darcy's law and a conservation of mass for a small control volume. The equation is often used to predict flow to wells, which have radial symmetry, so the flow equation is commonly solved in polar or cylindrical coordinates.
The Theis equation is one of the most commonly used and fundamental solutions to the groundwater flow equation; it can be used to predict the transient evolution of head due to the effects of pumping one or a number of pumping wells.
The Thiem equation is a solution to the steady state groundwater flow equation (Laplace's Equation). Unless there are large sources of water nearby (a river or lake), true steady-state is rarely achieved in reality.
Mineralogy
Mineralogy is the study of chemistry, crystal structure, and physical (including optical) properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.
History
Early writing on mineralogy, especially on gemstones, comes from ancient Babylonia, the ancient Greco-Roman world, ancient and medieval China, and Sanskrit texts from ancient India.[1] Books on the subject included the Naturalis Historia of Pliny the Elder which not only described many different minerals but also explained many of their properties. The German Renaissance specialist Georgius Agricola wrote works such as De re metallica (On Metals, 1556) and De Natura Fossilium (On the Nature of Rocks, 1546) which begin the scientific approach to the subject. Systematic scientific studies of minerals and rocks developed in post-Renaissance Europe.[2] The modern study of mineralogy was founded on the principles of crystallography and microscopic study of rock sections with the invention of the microscope in the 17th century.[2]
Modern mineralogy
Historically, mineralogy was heavily concerned with taxonomy of the rock-forming minerals; to this end, the International Mineralogical Association is an organization whose members represent mineralogists in individual countries. Its activities include managing the naming of minerals (via the Commission of New Minerals and Mineral Names), location of known minerals, etc. As of 2004 there are over 4,000 species of mineral recognized by the IMA. Of these, perhaps 150 can be called "common," another 50 are "occasional," and the rest are "rare" to "extremely rare."
More recently, driven by advances in experimental technique (such as neutron diffraction) and available computational power, the latter of which has enabled extremely accurate atomic-scale simulations of the behaviour of crystals, the science has branched out to consider more general problems in the fields of inorganic chemistry and solid-state physics. It, however, retains a focus on the crystal structures commonly encountered in rock-forming minerals (such as the perovskites, clay minerals and framework silicates). In particular, the field has made great advances in the understanding of the relationship between the atomic-scale structure of minerals and their function; in nature, prominent examples would be accurate measurement and prediction of the elastic properties of minerals, which has led to new insight into seismological behaviour of rocks and depth-related discontinuities in seismograms of the Earth's mantle. To this end, in their focus on the connection between atomic-scale phenomena and macroscopic properties, the mineral sciences (as they are now commonly known) display perhaps more of an overlap with materials science than any other discipline.
Physical mineralogy
Physical mineralogy is the specific focus on physical attributes of minerals. Description of physical attributes is the simplest way to identify, classify, and categorize minerals, and they include:[3]
* crystal structure
* crystal habit
* twinning
* cleavage
* luster
* color
* streak
* hardness
* specific gravity
Chemical mineralogy
Chemical mineralogy focuses on the chemical composition of minerals in order to identify, classify, and categorize them, as well as a means to find beneficial uses from them. There are a few minerals which are classified as whole elements, including sulfur, copper, silver, and gold, yet the vast majority of minerals are chemical compounds, some more complex than others.[4] In terms of major chemical divisions of minerals, most are placed within the isomorphous groups, which are based on analogous chemical composition and similar crystal forms. A good example of isomorphism classification would be the calcite group, containing the minerals calcite, magnesite, siderite, rhodochrosite, and smithsonite.[5]
[edit] Biomineralogy
Biomineralogy is a cross-over field between mineralogy, paleontology and biology. It is the study of how plants and animals stabilize minerals under biological control, and the sequencing of mineral replacement of those minerals after deposition.[6] It uses techniques from chemical mineralogy, especially isotopic studies, to determine such things as growth forms in living plants and animals[7][8] as well as things like the original mineral content of fossils.[9]
[edit] Optical mineralogy
Main article: Optical mineralogy
Optical mineralogy is a specific focus of mineralogy that applies sources of light as a means to identify and classify minerals. All minerals which are not part of the cubic system are double refracting, where ordinary light passing through them is broken up into two plane polarized rays that travel at different velocities and refracted at different angles. Mineral substances belonging to the cubic system pertain only one index of refraction.[5] Hexagonal and tetragonal mineral substances have two indices, while orthorhombic, monoclinic, and triclinic substances have three indices of refraction.[5] With opaque ore minerals, reflected light from a microscope is needed for identification.[5]
[edit] Crystal structure
Main article: Crystallography
X-rays are used to determine the atomic arrangements of minerals and so to identify and classify them. The arrangements of atoms define the crystal structures of the minerals. Some very fine-grained minerals, such as clays, commonly can be identified most readily by their crystal structures. The structure of a mineral also offers a precise way of establishing isomorphism.[5] With knowledge of atomic arrangements and compositions, one may deduce why minerals have specific physical properties [5], and one may calculate how those properties change with pressure and temperature.
[edit] Formation environments
The environments of mineral formation and growth are highly varied, ranging from slow crystallization at the high temperature and pressures of igneous melts deep within the Earth's crust to the low temperature precipitation from a saline brine at the Earth's surface.
Various possible methods of formation include:[10]
* sublimation from volcanic gases
* deposition from aqueous solutions and hydrothermal brines
* crystallization from an igneous magma or lava
* recrystallization due to metamorphic processes and metasomatism
* crystallization during diagenesis of sediments
* formation by oxidation and weathering of rocks exposed to the atmosphere or within the soil environment.
[edit] Uses
Minerals are essential to various needs within human society, such as minerals used for bettering health and fitness (such as mineral water or commercially-sold vitamins), essential components of metal products used in various commodities and machinery, essential components to building materials such as limestone, marble, granite, gravel, glass, plaster, cement, plastics, etc.[11] Minerals are also used in fertilizers to enrich the growth of agricultural crops.
[edit] Descriptive mineralogy
Descriptive mineralogy summarizes results of studies performed on mineral substances. It is the scholarly and scientific method of recording the identification, classification, and categorization of minerals, their properties, and their uses. Classifications for descriptive mineralogy includes:[12][13]
* native elements
* sulfides
* oxides and hydroxides
* halides
* carbonates, nitrates and borates
* sulfates, chromates, molybdates and tungstates
* phosphates, arsenates and vanadates
* silicates
* organic minerals
[edit] Determinative mineralogy
Determinative mineralogy is the actual scientific process of identifying minerals, through data gathering and conclusion. When new minerals are discovered, a standard procedure of scientific analysis is followed, including measures to identify a mineral's formula, its crystallographic data, its optical data, as well as the general physical attributes determined and listed.
History
Early writing on mineralogy, especially on gemstones, comes from ancient Babylonia, the ancient Greco-Roman world, ancient and medieval China, and Sanskrit texts from ancient India.[1] Books on the subject included the Naturalis Historia of Pliny the Elder which not only described many different minerals but also explained many of their properties. The German Renaissance specialist Georgius Agricola wrote works such as De re metallica (On Metals, 1556) and De Natura Fossilium (On the Nature of Rocks, 1546) which begin the scientific approach to the subject. Systematic scientific studies of minerals and rocks developed in post-Renaissance Europe.[2] The modern study of mineralogy was founded on the principles of crystallography and microscopic study of rock sections with the invention of the microscope in the 17th century.[2]
Modern mineralogy
Historically, mineralogy was heavily concerned with taxonomy of the rock-forming minerals; to this end, the International Mineralogical Association is an organization whose members represent mineralogists in individual countries. Its activities include managing the naming of minerals (via the Commission of New Minerals and Mineral Names), location of known minerals, etc. As of 2004 there are over 4,000 species of mineral recognized by the IMA. Of these, perhaps 150 can be called "common," another 50 are "occasional," and the rest are "rare" to "extremely rare."
More recently, driven by advances in experimental technique (such as neutron diffraction) and available computational power, the latter of which has enabled extremely accurate atomic-scale simulations of the behaviour of crystals, the science has branched out to consider more general problems in the fields of inorganic chemistry and solid-state physics. It, however, retains a focus on the crystal structures commonly encountered in rock-forming minerals (such as the perovskites, clay minerals and framework silicates). In particular, the field has made great advances in the understanding of the relationship between the atomic-scale structure of minerals and their function; in nature, prominent examples would be accurate measurement and prediction of the elastic properties of minerals, which has led to new insight into seismological behaviour of rocks and depth-related discontinuities in seismograms of the Earth's mantle. To this end, in their focus on the connection between atomic-scale phenomena and macroscopic properties, the mineral sciences (as they are now commonly known) display perhaps more of an overlap with materials science than any other discipline.
Physical mineralogy
Physical mineralogy is the specific focus on physical attributes of minerals. Description of physical attributes is the simplest way to identify, classify, and categorize minerals, and they include:[3]
* crystal structure
* crystal habit
* twinning
* cleavage
* luster
* color
* streak
* hardness
* specific gravity
Chemical mineralogy
Chemical mineralogy focuses on the chemical composition of minerals in order to identify, classify, and categorize them, as well as a means to find beneficial uses from them. There are a few minerals which are classified as whole elements, including sulfur, copper, silver, and gold, yet the vast majority of minerals are chemical compounds, some more complex than others.[4] In terms of major chemical divisions of minerals, most are placed within the isomorphous groups, which are based on analogous chemical composition and similar crystal forms. A good example of isomorphism classification would be the calcite group, containing the minerals calcite, magnesite, siderite, rhodochrosite, and smithsonite.[5]
[edit] Biomineralogy
Biomineralogy is a cross-over field between mineralogy, paleontology and biology. It is the study of how plants and animals stabilize minerals under biological control, and the sequencing of mineral replacement of those minerals after deposition.[6] It uses techniques from chemical mineralogy, especially isotopic studies, to determine such things as growth forms in living plants and animals[7][8] as well as things like the original mineral content of fossils.[9]
[edit] Optical mineralogy
Main article: Optical mineralogy
Optical mineralogy is a specific focus of mineralogy that applies sources of light as a means to identify and classify minerals. All minerals which are not part of the cubic system are double refracting, where ordinary light passing through them is broken up into two plane polarized rays that travel at different velocities and refracted at different angles. Mineral substances belonging to the cubic system pertain only one index of refraction.[5] Hexagonal and tetragonal mineral substances have two indices, while orthorhombic, monoclinic, and triclinic substances have three indices of refraction.[5] With opaque ore minerals, reflected light from a microscope is needed for identification.[5]
[edit] Crystal structure
Main article: Crystallography
X-rays are used to determine the atomic arrangements of minerals and so to identify and classify them. The arrangements of atoms define the crystal structures of the minerals. Some very fine-grained minerals, such as clays, commonly can be identified most readily by their crystal structures. The structure of a mineral also offers a precise way of establishing isomorphism.[5] With knowledge of atomic arrangements and compositions, one may deduce why minerals have specific physical properties [5], and one may calculate how those properties change with pressure and temperature.
[edit] Formation environments
The environments of mineral formation and growth are highly varied, ranging from slow crystallization at the high temperature and pressures of igneous melts deep within the Earth's crust to the low temperature precipitation from a saline brine at the Earth's surface.
Various possible methods of formation include:[10]
* sublimation from volcanic gases
* deposition from aqueous solutions and hydrothermal brines
* crystallization from an igneous magma or lava
* recrystallization due to metamorphic processes and metasomatism
* crystallization during diagenesis of sediments
* formation by oxidation and weathering of rocks exposed to the atmosphere or within the soil environment.
[edit] Uses
Minerals are essential to various needs within human society, such as minerals used for bettering health and fitness (such as mineral water or commercially-sold vitamins), essential components of metal products used in various commodities and machinery, essential components to building materials such as limestone, marble, granite, gravel, glass, plaster, cement, plastics, etc.[11] Minerals are also used in fertilizers to enrich the growth of agricultural crops.
[edit] Descriptive mineralogy
Descriptive mineralogy summarizes results of studies performed on mineral substances. It is the scholarly and scientific method of recording the identification, classification, and categorization of minerals, their properties, and their uses. Classifications for descriptive mineralogy includes:[12][13]
* native elements
* sulfides
* oxides and hydroxides
* halides
* carbonates, nitrates and borates
* sulfates, chromates, molybdates and tungstates
* phosphates, arsenates and vanadates
* silicates
* organic minerals
[edit] Determinative mineralogy
Determinative mineralogy is the actual scientific process of identifying minerals, through data gathering and conclusion. When new minerals are discovered, a standard procedure of scientific analysis is followed, including measures to identify a mineral's formula, its crystallographic data, its optical data, as well as the general physical attributes determined and listed.
Crystallography
Crystallography is the experimental science of determining the arrangement of atoms in solids. In older usage, it is the scientific study of crystals. The word "crystallography" is derived from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write.
Before the development of X-ray diffraction crystallography (see below), the study of crystals was based on the geometry of the crystals. This involves measuring the angles of crystal faces relative to theoretical reference axes (crystallographic axes), and establishing the symmetry of the crystal in question. The former is carried out using a goniometer. The position in 3D space of each crystal face is plotted on a stereographic net, e.g. Wulff net or Lambert net. In fact, the pole to each face is plotted on the net. Each point is labelled with its Miller index. The final plot allows the symmetry of the crystal to be established.
Crystallographic methods now depend on the analysis of the diffraction patterns that emerge from a sample that is targeted by a beam of some type. The beam is not always electromagnetic radiation, even though X-rays are the most common choice. For some purposes electrons or neutrons are used, which is possible due to the wave properties of the particles. Crystallographers often explicitly state the type of illumination used when referring to a method, as with the terms X-ray diffraction, neutron diffraction and electron diffraction.
These three types of radiation interact with the specimen in different ways. X-rays interact with the spatial distribution of the valence electrons, while electrons are charged particles and therefore feel the total charge distribution of both the atomic nuclei and the surrounding electrons. Neutrons are scattered by the atomic nuclei through the strong nuclear forces, but in addition, the magnetic moment of neutrons is non-zero. They are therefore also scattered by magnetic fields. When neutrons are scattered from hydrogen-containing materials, they produce diffraction patterns with high noise levels. However, the material can sometimes be treated to substitute hydrogen for deuterium. Because of these different forms of interaction, the three types of radiation are suitable for different crystallographic studies
Theory
Condensed matter physics
Linbo3 Unit Cell.png
Phases · Phase transition
[show]States of matter
Solid · Liquid · Gas · Bose-Einstein condensate · Fermionic condensate · Fermi gas · Fermi liquid · Supersolid · Superfluid · Luttinger liquid
[show]Phase phenomena
Order parameter · Phase transition
[show]Electronic phases
Insulator · Mott insulator · Semiconductor · Semimetal · Conductor · Superconductor · Thermoelectric · Piezoelectric · Ferroelectric
[show]Electronic phenomena
Quantum Hall effect · Spin Hall effect · Kondo effect
[show]Magnetic phases
Diamagnet · Superdiamagnet
Paramagnet · Superparamagnet
Ferromagnet · Antiferromagnet
Ferrimagnet · Metamagnet
Spin glass
[show]Quasiparticles
Phonon · Exciton · Plasmon
Polariton · Polaron · Magnon
[show]Soft matter
Amorphous solid · Granular matter ·
Liquid crystal · Polymer
[show]Scientists
Maxwell · Van der Waals · Debye · Bloch · Onsager · Mott · Peierls · Landau · Luttinger · Anderson · Bardeen · Cooper · Schrieffer · Josephson · Landau · Kohn · Kadanoff · Fisher
This box: view • talk • edit
An image of a small object is usually generated by using a lens to focus the illuminating radiation, as is done with the rays of the visible spectrum in light microscopy. However, the wavelength of visible light (about 4000 to 7000 angstroms) is three orders of magnitude longer then the length of typical atomic bonds and atoms themselves (about 1 to 2 angstroms). Therefore, obtaining information about the spatial arrangement of atoms requires the use of radiation with shorter wavelengths, such as X-rays. Employing shorter wavelengths implied abandoning microscopy and true imaging, however, because there exists no material from which a lens capable of focusing this type of radiation can be created. (That said, scientists have had some success focusing X-rays with microscopic Fresnel zone plates made from gold, and by critical-angle reflection inside long tapered capillaries.)[1] Diffracted x-ray beams cannot be focused to produce images, so the sample structure must be reconstructed from the diffraction pattern. Sharp features in the diffraction pattern arise from periodic, repeating structure in the sample, which are often very strong due to coherent reflection of many photons from many regularly spaced instances of similar structure, while non-periodic components of the structure result in diffuse (and usually weak) diffraction features.
Because of their highly ordered and repetitive structure, crystals give diffraction patterns of sharp Bragg reflection spots, and are ideal for analyzing the structure of solids.
Before the development of X-ray diffraction crystallography (see below), the study of crystals was based on the geometry of the crystals. This involves measuring the angles of crystal faces relative to theoretical reference axes (crystallographic axes), and establishing the symmetry of the crystal in question. The former is carried out using a goniometer. The position in 3D space of each crystal face is plotted on a stereographic net, e.g. Wulff net or Lambert net. In fact, the pole to each face is plotted on the net. Each point is labelled with its Miller index. The final plot allows the symmetry of the crystal to be established.
Crystallographic methods now depend on the analysis of the diffraction patterns that emerge from a sample that is targeted by a beam of some type. The beam is not always electromagnetic radiation, even though X-rays are the most common choice. For some purposes electrons or neutrons are used, which is possible due to the wave properties of the particles. Crystallographers often explicitly state the type of illumination used when referring to a method, as with the terms X-ray diffraction, neutron diffraction and electron diffraction.
These three types of radiation interact with the specimen in different ways. X-rays interact with the spatial distribution of the valence electrons, while electrons are charged particles and therefore feel the total charge distribution of both the atomic nuclei and the surrounding electrons. Neutrons are scattered by the atomic nuclei through the strong nuclear forces, but in addition, the magnetic moment of neutrons is non-zero. They are therefore also scattered by magnetic fields. When neutrons are scattered from hydrogen-containing materials, they produce diffraction patterns with high noise levels. However, the material can sometimes be treated to substitute hydrogen for deuterium. Because of these different forms of interaction, the three types of radiation are suitable for different crystallographic studies
Theory
Condensed matter physics
Linbo3 Unit Cell.png
Phases · Phase transition
[show]States of matter
Solid · Liquid · Gas · Bose-Einstein condensate · Fermionic condensate · Fermi gas · Fermi liquid · Supersolid · Superfluid · Luttinger liquid
[show]Phase phenomena
Order parameter · Phase transition
[show]Electronic phases
Insulator · Mott insulator · Semiconductor · Semimetal · Conductor · Superconductor · Thermoelectric · Piezoelectric · Ferroelectric
[show]Electronic phenomena
Quantum Hall effect · Spin Hall effect · Kondo effect
[show]Magnetic phases
Diamagnet · Superdiamagnet
Paramagnet · Superparamagnet
Ferromagnet · Antiferromagnet
Ferrimagnet · Metamagnet
Spin glass
[show]Quasiparticles
Phonon · Exciton · Plasmon
Polariton · Polaron · Magnon
[show]Soft matter
Amorphous solid · Granular matter ·
Liquid crystal · Polymer
[show]Scientists
Maxwell · Van der Waals · Debye · Bloch · Onsager · Mott · Peierls · Landau · Luttinger · Anderson · Bardeen · Cooper · Schrieffer · Josephson · Landau · Kohn · Kadanoff · Fisher
This box: view • talk • edit
An image of a small object is usually generated by using a lens to focus the illuminating radiation, as is done with the rays of the visible spectrum in light microscopy. However, the wavelength of visible light (about 4000 to 7000 angstroms) is three orders of magnitude longer then the length of typical atomic bonds and atoms themselves (about 1 to 2 angstroms). Therefore, obtaining information about the spatial arrangement of atoms requires the use of radiation with shorter wavelengths, such as X-rays. Employing shorter wavelengths implied abandoning microscopy and true imaging, however, because there exists no material from which a lens capable of focusing this type of radiation can be created. (That said, scientists have had some success focusing X-rays with microscopic Fresnel zone plates made from gold, and by critical-angle reflection inside long tapered capillaries.)[1] Diffracted x-ray beams cannot be focused to produce images, so the sample structure must be reconstructed from the diffraction pattern. Sharp features in the diffraction pattern arise from periodic, repeating structure in the sample, which are often very strong due to coherent reflection of many photons from many regularly spaced instances of similar structure, while non-periodic components of the structure result in diffuse (and usually weak) diffraction features.
Because of their highly ordered and repetitive structure, crystals give diffraction patterns of sharp Bragg reflection spots, and are ideal for analyzing the structure of solids.
Stratigraphy
Stratigraphy
Historical development
Engraving from William Smith's monograph on identifying strata based on fossils
Rock layers were studied since the time of Avicenna (Ibn Sina), a Muslim geographer who wrote The Book of Healing in 1027. He was the first to outline the law of superposition of strata:[1]
"It is also possible that the sea may have happened to flow little by little over the land consisting of both plain and mountain, and then have ebbed away from it. ... It is possible that each time the land was exposed by the ebbing of the sea a layer was left, since we see that some mountains appear to have been piled up layer by layer, and it is therefore likely that the clay from which they were formed was itself at one time arranged in layers. One layer was formed first, then at a different period, a further was formed and piled, upon the first, and so on. Over each layer there spread a substance of different material, which formed a partition between it and the next layer; but when petrification took place something occurred to the partition which caused it to break up and disintegrate from between the layers (possibly referring to unconformity). ... As to the beginning of the sea, its clay is either sedimentary or primeval, the latter not being sedimentary. It is probable that the sedimentary clay was formed by the disintegration of the strata of mountains. Such is the formation of mountains."
The theoretical basis for the subject was established by Nicholas Steno who re-introduced the law of superposition and introduced the principle of original horizontality and principle of lateral continuity in a 1669 work on the fossilization of organic remains in layers of sediment.
The first practical large scale application of stratigraphy was by William Smith in the 1790s and early 1800s. Smith, known as the Father of English Geology, created the first geologic map of England, and first recognized the significance of strata or rock layering, and the importance of fossil markers for correlating strata. Another influential application of stratigraphy in the early 1800s was a study by Georges Cuvier and Alexandre Brongniart of the geology of the region around Paris.
Lithologic stratigraphy
Main article: Lithostratigraphy
Chalk Layers in Cyprus - showing sedimentary layering
Lithostratigraphy, or lithologic stratigraphy, is the most obvious. It deals with the physical lithologic, or rock type, change both vertically in layering or bedding of varying rock type and laterally reflecting changing environments of deposition, known as facies change. Key elements of stratigraphy involve understanding how certain geometric relationships between rock layers arise and what these geometries mean in terms of depositional environment. One of stratigraphy's basic concepts is codified in the Law of Superposition, which simply states that, in an undeformed stratigraphic sequence, the oldest strata occur at the base of the sequence.
Chemostratigraphy is based on the changes in the relative proportions of trace elements and isotopes within and between lithologic units. Carbon and oxygen isotope ratios vary with time and are used to map subtle changes in the paleoenvironment. This has led to the specialized field of isotopic stratigraphy.
Cyclostratigraphy documents the often cyclic changes in the relative proportions of minerals, particularly carbonates, and fossil diversity with time, related to changes in palaeoclimates.
Biostratigraphy
Main article: Biostratigraphy
Biostratigraphy or paleontologic stratigraphy is based on fossil evidence in the rock layers. Strata from widespread locations containing the same fossil fauna and flora are correlatable in time. Biologic stratigraphy was based on William Smith's principle of faunal succession, which predated, and was one of the first and most powerful lines of evidence for, biological evolution. It provides strong evidence for formation (speciation) of and the extinction of species. The geologic time scale was developed during the 1800s based on the evidence of biologic stratigraphy and faunal succession. This timescale remained a relative scale until the development of radiometric dating, which gave it and the stratigraphy it was based on an absolute time framework, leading to the development of chronostratigraphy.
One important development is the Vail curve, which attempts to define a global historical sea-level curve according to inferences from world-wide stratigraphic patterns. Stratigraphy is also commonly used to delineate the nature and extent of hydrocarbon-bearing reservoir rocks, seals and traps in petroleum geology.
[edit] Chronostratigraphy
Main article: Chronostratigraphy
Chronostratigraphy is the branch of stratigraphy that studies the relative, not absolute, age of rock strata.
Chronostratigraphy is based upon deriving geochronological data for rock units, both directly and by inference, so that a sequence of time relative events of rocks within a region can be derived. In essence, chronostratigraphy seeks to understand the geologic history of rocks and regions.
The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of the Earth.
Magnetostratigraphy
Main article: Magnetostratigraphy
Magnetostratigraphy is a chronostratigraphic technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their detrital remnant magnetism (DRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. This is possible because when very fine-grained magnetic minerals (< 17 micrometres) fall through the water column, they orient themselves with Earth's magnetic field. Upon burial, that orientation is preserved. The minerals, in effect, behave like tiny compasses.
Oriented paleomagnetic core samples are collected in the field; mudstones, siltstones, and very fine-grained sandstones are the preferred lithologies because the magnetic grains are finer and more likely to orient with the ambient field during deposition. If the ancient magnetic field was oriented similar to today's field (North Magnetic Pole near the North Rotational Pole) the strata retain a normal polarity. If the data indicate that the North Magnetic Pole was near the South Rotational Pole, the strata exhibit reversed polarity.
Results of the individual samples are analysed by removing the natural remnant magnetism(NRM) to reveal the DRM. Following statistical analysis the results are used to generate a local magnetostratigraphic column that can then be compared against the Global Magnetic Polarity Time Scale.
This technique is used to date sequences that generally lack fossils or interbedded igneous rocks. The continuous nature of the sampling means that it is also a powerful technique for the estimation of sediment accumulation rates.
Archaeological stratigraphy
Main article: Archaeological stratigraphy
In the field of archaeology, soil stratigraphy is used to better understand the processes that form and protect archaeological sites. The law of superposition holds true, and this can help date finds or features from each context, as they can be placed in sequence and the dates interpolated. Phases of activity can also often be seen through stratigraphy, especially when a trench or feature is viewed in section (profile). As pits and other features can be dug down into earlier levels, not all material at the same absolute depth is necessarily of the same age, but close attention has to be paid to the archeological layers. The Harris-matrix is a tool to depict complex stratigraphic relations, as they are found, for example, in the contexts of urban archaeology.
Historical development
Engraving from William Smith's monograph on identifying strata based on fossils
Rock layers were studied since the time of Avicenna (Ibn Sina), a Muslim geographer who wrote The Book of Healing in 1027. He was the first to outline the law of superposition of strata:[1]
"It is also possible that the sea may have happened to flow little by little over the land consisting of both plain and mountain, and then have ebbed away from it. ... It is possible that each time the land was exposed by the ebbing of the sea a layer was left, since we see that some mountains appear to have been piled up layer by layer, and it is therefore likely that the clay from which they were formed was itself at one time arranged in layers. One layer was formed first, then at a different period, a further was formed and piled, upon the first, and so on. Over each layer there spread a substance of different material, which formed a partition between it and the next layer; but when petrification took place something occurred to the partition which caused it to break up and disintegrate from between the layers (possibly referring to unconformity). ... As to the beginning of the sea, its clay is either sedimentary or primeval, the latter not being sedimentary. It is probable that the sedimentary clay was formed by the disintegration of the strata of mountains. Such is the formation of mountains."
The theoretical basis for the subject was established by Nicholas Steno who re-introduced the law of superposition and introduced the principle of original horizontality and principle of lateral continuity in a 1669 work on the fossilization of organic remains in layers of sediment.
The first practical large scale application of stratigraphy was by William Smith in the 1790s and early 1800s. Smith, known as the Father of English Geology, created the first geologic map of England, and first recognized the significance of strata or rock layering, and the importance of fossil markers for correlating strata. Another influential application of stratigraphy in the early 1800s was a study by Georges Cuvier and Alexandre Brongniart of the geology of the region around Paris.
Lithologic stratigraphy
Main article: Lithostratigraphy
Chalk Layers in Cyprus - showing sedimentary layering
Lithostratigraphy, or lithologic stratigraphy, is the most obvious. It deals with the physical lithologic, or rock type, change both vertically in layering or bedding of varying rock type and laterally reflecting changing environments of deposition, known as facies change. Key elements of stratigraphy involve understanding how certain geometric relationships between rock layers arise and what these geometries mean in terms of depositional environment. One of stratigraphy's basic concepts is codified in the Law of Superposition, which simply states that, in an undeformed stratigraphic sequence, the oldest strata occur at the base of the sequence.
Chemostratigraphy is based on the changes in the relative proportions of trace elements and isotopes within and between lithologic units. Carbon and oxygen isotope ratios vary with time and are used to map subtle changes in the paleoenvironment. This has led to the specialized field of isotopic stratigraphy.
Cyclostratigraphy documents the often cyclic changes in the relative proportions of minerals, particularly carbonates, and fossil diversity with time, related to changes in palaeoclimates.
Biostratigraphy
Main article: Biostratigraphy
Biostratigraphy or paleontologic stratigraphy is based on fossil evidence in the rock layers. Strata from widespread locations containing the same fossil fauna and flora are correlatable in time. Biologic stratigraphy was based on William Smith's principle of faunal succession, which predated, and was one of the first and most powerful lines of evidence for, biological evolution. It provides strong evidence for formation (speciation) of and the extinction of species. The geologic time scale was developed during the 1800s based on the evidence of biologic stratigraphy and faunal succession. This timescale remained a relative scale until the development of radiometric dating, which gave it and the stratigraphy it was based on an absolute time framework, leading to the development of chronostratigraphy.
One important development is the Vail curve, which attempts to define a global historical sea-level curve according to inferences from world-wide stratigraphic patterns. Stratigraphy is also commonly used to delineate the nature and extent of hydrocarbon-bearing reservoir rocks, seals and traps in petroleum geology.
[edit] Chronostratigraphy
Main article: Chronostratigraphy
Chronostratigraphy is the branch of stratigraphy that studies the relative, not absolute, age of rock strata.
Chronostratigraphy is based upon deriving geochronological data for rock units, both directly and by inference, so that a sequence of time relative events of rocks within a region can be derived. In essence, chronostratigraphy seeks to understand the geologic history of rocks and regions.
The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of the Earth.
Magnetostratigraphy
Main article: Magnetostratigraphy
Magnetostratigraphy is a chronostratigraphic technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their detrital remnant magnetism (DRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. This is possible because when very fine-grained magnetic minerals (< 17 micrometres) fall through the water column, they orient themselves with Earth's magnetic field. Upon burial, that orientation is preserved. The minerals, in effect, behave like tiny compasses.
Oriented paleomagnetic core samples are collected in the field; mudstones, siltstones, and very fine-grained sandstones are the preferred lithologies because the magnetic grains are finer and more likely to orient with the ambient field during deposition. If the ancient magnetic field was oriented similar to today's field (North Magnetic Pole near the North Rotational Pole) the strata retain a normal polarity. If the data indicate that the North Magnetic Pole was near the South Rotational Pole, the strata exhibit reversed polarity.
Results of the individual samples are analysed by removing the natural remnant magnetism(NRM) to reveal the DRM. Following statistical analysis the results are used to generate a local magnetostratigraphic column that can then be compared against the Global Magnetic Polarity Time Scale.
This technique is used to date sequences that generally lack fossils or interbedded igneous rocks. The continuous nature of the sampling means that it is also a powerful technique for the estimation of sediment accumulation rates.
Archaeological stratigraphy
Main article: Archaeological stratigraphy
In the field of archaeology, soil stratigraphy is used to better understand the processes that form and protect archaeological sites. The law of superposition holds true, and this can help date finds or features from each context, as they can be placed in sequence and the dates interpolated. Phases of activity can also often be seen through stratigraphy, especially when a trench or feature is viewed in section (profile). As pits and other features can be dug down into earlier levels, not all material at the same absolute depth is necessarily of the same age, but close attention has to be paid to the archeological layers. The Harris-matrix is a tool to depict complex stratigraphic relations, as they are found, for example, in the contexts of urban archaeology.
Paleontology
Paleontology (British: palaeontology)[derivation 1] is the study of prehistoric life, including organisms' evolution and interactions with each other and their environments (their paleoecology). As a "historical science" it tries to explain causes rather than conduct experiments to observe effects. Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. Fossils found in China since the 1990s have provided new information about the earliest evolution of animals, early fish, dinosaurs and the evolution of birds and mammals. Paleontology lies on the border between biology and geology, and shares with archaeology a border that is difficult to define. It now uses techniques drawn from a wide range of sciences, including biochemistry, mathematics and engineering. As knowledge has increased, paleontology has developed specialized subdivisions, some of which focus on different types of fossil organisms while others study ecological and environmental history, such as ancient climates.
Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy. Classifying ancient organisms is also difficult, as many do not fit well into the Linnean taxonomy that is commonly used for classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics, which investigates how closely organisms are related by measuring how similar the DNA is in their genomes. Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend.
Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life, almost all the way back to when Earth became capable of supporting life, about 3,800 million years ago. For about half of that time the only life was single-celled micro-organisms, mostly in microbial mats that formed ecosystems only a few millimeters thick. Earth's atmosphere originally contained virtually no oxygen, and its oxygenation began about 2,400 million years ago. This may have caused an accelerating increase in the diversity and complexity of life, and early multicellular plants and fungi have been found in rocks dated from 1,700 to 1,200 million years ago. The earliest multicellular animal fossils are much later, from about 580 million years ago, but animals diversified very rapidly and there is a lively debate about whether most of this happened in a relatively short Cambrian explosion or started earlier but has been hidden by lack of fossils. All of these organisms lived in water, but plants and invertebrates started colonizing land from about 490 million years ago and vertebrates followed them about 370 million years ago. The first dinosaurs appeared about 230 million years ago and birds evolved from one dinosaur group about 150 million years ago. During the time of the dinosaurs, mammals' ancestors survived only as small, mainly nocturnal insectivores, but after the non-avian dinosaurs became extinct in the Cretaceous–Tertiary extinction event 65 million years ago mammals diversified rapidly. Flowering plants appeared and rapidly diversified between 130 million years ago and 90 million years ago, possibly helped by coevolution with pollinating insects. Social insects appeared around the same time and, although they have relatively few species, now form over 50% of the total mass of all insects. The upright-walking common ancestor of humans and chimpanzees Sahelanthropus tchadensis appeared around 6 to 7 million years ago, and anatomically modern humans appeared under 200,000 years ago. The course of evolution has been changed several times by mass extinctions that wiped out previously dominant groups and allowed other to rise from obscurity to become major components of ecosystems.
Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy. Classifying ancient organisms is also difficult, as many do not fit well into the Linnean taxonomy that is commonly used for classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics, which investigates how closely organisms are related by measuring how similar the DNA is in their genomes. Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend.
Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life, almost all the way back to when Earth became capable of supporting life, about 3,800 million years ago. For about half of that time the only life was single-celled micro-organisms, mostly in microbial mats that formed ecosystems only a few millimeters thick. Earth's atmosphere originally contained virtually no oxygen, and its oxygenation began about 2,400 million years ago. This may have caused an accelerating increase in the diversity and complexity of life, and early multicellular plants and fungi have been found in rocks dated from 1,700 to 1,200 million years ago. The earliest multicellular animal fossils are much later, from about 580 million years ago, but animals diversified very rapidly and there is a lively debate about whether most of this happened in a relatively short Cambrian explosion or started earlier but has been hidden by lack of fossils. All of these organisms lived in water, but plants and invertebrates started colonizing land from about 490 million years ago and vertebrates followed them about 370 million years ago. The first dinosaurs appeared about 230 million years ago and birds evolved from one dinosaur group about 150 million years ago. During the time of the dinosaurs, mammals' ancestors survived only as small, mainly nocturnal insectivores, but after the non-avian dinosaurs became extinct in the Cretaceous–Tertiary extinction event 65 million years ago mammals diversified rapidly. Flowering plants appeared and rapidly diversified between 130 million years ago and 90 million years ago, possibly helped by coevolution with pollinating insects. Social insects appeared around the same time and, although they have relatively few species, now form over 50% of the total mass of all insects. The upright-walking common ancestor of humans and chimpanzees Sahelanthropus tchadensis appeared around 6 to 7 million years ago, and anatomically modern humans appeared under 200,000 years ago. The course of evolution has been changed several times by mass extinctions that wiped out previously dominant groups and allowed other to rise from obscurity to become major components of ecosystems.
Geomorphology
Geomorphology (from Greek: γῆ, ge, "earth"; μορφή, morfé, "form"; and λόγος, logos, "study") is the scientific study of landforms and the processes that shape them. Geomorphologists seek to understand why landscapes look the way they do: to understand landform history and dynamics, and predict future changes through a combination of field observation, physical experiment, and numerical modeling. Geomorphology is practiced within geography, geology, geodesy, engineering geology, archaeology, and geotechnical engineering. Early studies in geomorphology are the foundation for pedology, one of two main branches of soil science.
Landforms evolve in response to a combination of natural and anthropogenic processes. The landscape is built up through tectonic uplift and volcanism. Denudation occurs by erosion and mass wasting, which produces sediment that is transported and deposited elsewhere within the landscape or off the coast. Landscapes are also lowered by subsidence, either due to tectonics or physical changes in underlying sedimentary deposits. These processes are each influenced differently by climate, ecology, and human activity.
Practical applications of geomorphology include hazard assessment including landslide prediction and mitigation, river control and restoration, and coastal protection.
History
Perhaps the earliest one to devise a theory of geomorphology was the polymath Chinese scientist and statesman Shen Kuo (1031-1095 AD). This was based on his observation of marine fossil shells in a geological stratum of a mountain hundreds of miles from the Pacific Ocean. Noticing bivalve shells running in a horizontal span along the cut section of a cliffside, he theorized that the cliff was once the pre-historic location of a seashore that had shifted hundreds of miles over the centuries. He inferred that the land was reshaped and formed by soil erosion of the mountains and by deposition of silt, after observing strange natural erosions of the Taihang Mountains and the Yandang Mountain near Wenzhou. Furthermore, he promoted the theory of gradual climate change over centuries of time once ancient petrified bamboos were found to be preserved underground in the dry, northern climate zone of Yanzhou, which is now modern day Yan'an, Shaanxi province.
The first geomorphic model was the geographical cycle or the cycle of erosion, developed by William Morris Davis between 1884 and 1899. The cycle was inspired by theories of uniformitarianism which were first formulated by James Hutton (1726-1797). Concerning valley forms, the cycle was depicted as a sequence by which a river would cut a valley more and more deeply, but then erosion of side valleys would eventually flatten out the terrain again, now at a lower elevation. The cycle could be started over by uplift of the terrain. The model is today considered too much of a simplification to be especially useful in practice..
Walther Penck developed an alternative model in the 1920s, based on ratios of uplift and erosion, but it was also too weak to explain a variety of landforms. Grove Karl Gilbert was an important early American geomorphologist.
Landforms evolve in response to a combination of natural and anthropogenic processes. The landscape is built up through tectonic uplift and volcanism. Denudation occurs by erosion and mass wasting, which produces sediment that is transported and deposited elsewhere within the landscape or off the coast. Landscapes are also lowered by subsidence, either due to tectonics or physical changes in underlying sedimentary deposits. These processes are each influenced differently by climate, ecology, and human activity.
Practical applications of geomorphology include hazard assessment including landslide prediction and mitigation, river control and restoration, and coastal protection.
History
Perhaps the earliest one to devise a theory of geomorphology was the polymath Chinese scientist and statesman Shen Kuo (1031-1095 AD). This was based on his observation of marine fossil shells in a geological stratum of a mountain hundreds of miles from the Pacific Ocean. Noticing bivalve shells running in a horizontal span along the cut section of a cliffside, he theorized that the cliff was once the pre-historic location of a seashore that had shifted hundreds of miles over the centuries. He inferred that the land was reshaped and formed by soil erosion of the mountains and by deposition of silt, after observing strange natural erosions of the Taihang Mountains and the Yandang Mountain near Wenzhou. Furthermore, he promoted the theory of gradual climate change over centuries of time once ancient petrified bamboos were found to be preserved underground in the dry, northern climate zone of Yanzhou, which is now modern day Yan'an, Shaanxi province.
The first geomorphic model was the geographical cycle or the cycle of erosion, developed by William Morris Davis between 1884 and 1899. The cycle was inspired by theories of uniformitarianism which were first formulated by James Hutton (1726-1797). Concerning valley forms, the cycle was depicted as a sequence by which a river would cut a valley more and more deeply, but then erosion of side valleys would eventually flatten out the terrain again, now at a lower elevation. The cycle could be started over by uplift of the terrain. The model is today considered too much of a simplification to be especially useful in practice..
Walther Penck developed an alternative model in the 1920s, based on ratios of uplift and erosion, but it was also too weak to explain a variety of landforms. Grove Karl Gilbert was an important early American geomorphologist.
Friday, March 12, 2010
Sedimentology
Sedimentology encompasses the study of modern sediments such as sand,[1] mud (silt),[2] and clay,[3] and the processes that result in their deposition.[4] Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of sedimentary rocks and sedimentary structures.[5]
Sedimentary rocks cover most of the Earth's surface, record much of the Earth's history, and harbor the fossil record. Sedimentology is closely linked to stratigraphy, the study of the physical and temporal relationships between rock layers or strata.
The premise that the processes affecting the earth today are the same as in the past is the basis for determining how sedimentary features in the rock record were formed. By comparing similar features today to features in the rock record—for example, by comparing modern sand dunes to dunes preserved in ancient aeolian sandstones—geologists reconstruct past environments.
Sedimentary rocks cover most of the Earth's surface, record much of the Earth's history, and harbor the fossil record. Sedimentology is closely linked to stratigraphy, the study of the physical and temporal relationships between rock layers or strata.
The premise that the processes affecting the earth today are the same as in the past is the basis for determining how sedimentary features in the rock record were formed. By comparing similar features today to features in the rock record—for example, by comparing modern sand dunes to dunes preserved in ancient aeolian sandstones—geologists reconstruct past environments.
Fields and related disciplines
Fields
* Geodesy,[1] measurement of the Earth: GPS, vertical and horizontal motions of the Earth's surface, navigation, the study of the Earth's gravitational field, and the size and form of the Earth
* The study of large-scale motions of the Earth's surface and interior, including:
* Tectonophysics, the study of the physical processes that cause and result from plate tectonics
* Geodynamics, the study of modes of transport deformation within the Earth: rock deformation, mantle flow and convection, heat flow, lithosphere dynamics
* Seismology, the study of earthquakes and the propagation of elastic waves through the Earth
* Most of our knowledge of the Structure of the Earth is derived from seismology
* Shallow seismology is used in exploration geophysics (to find oil and gas) and for environmental characterization of the subsurface
* Geomagnetism, the study of the Earth's magnetic field, including its origin, telluric currents driven by the magnetic field, the Van Allen belts, and the interaction between the magnetosphere and the solar wind. This field is associated with paleomagnetism, or the measurement of the orientation of the Earth's magnetic field over the geologic past.
* Mathematical Geophysics, The development and applications of mathematical methods [2] and techniques for the solution of geophysical problems.[3]
* Geophysical surveying:
* Exploration and engineering geophysics, using surface methods to detect or infer the presence and position of concentrations of ore minerals and hydrocarbons
* Archaeological geophysics, for archaeological imaging or mapping
* Environmental and Engineering Geophysics, for locating underground storage tanks (UST's) or utilities, delineating landfills, locating voids or potential subsidence, finding depth to, P-wave or S-wave velocity of, or rippability of bedrock, or the pathway of groundwater movement
* Geodesy,[1] measurement of the Earth: GPS, vertical and horizontal motions of the Earth's surface, navigation, the study of the Earth's gravitational field, and the size and form of the Earth
* The study of large-scale motions of the Earth's surface and interior, including:
* Tectonophysics, the study of the physical processes that cause and result from plate tectonics
* Geodynamics, the study of modes of transport deformation within the Earth: rock deformation, mantle flow and convection, heat flow, lithosphere dynamics
* Seismology, the study of earthquakes and the propagation of elastic waves through the Earth
* Most of our knowledge of the Structure of the Earth is derived from seismology
* Shallow seismology is used in exploration geophysics (to find oil and gas) and for environmental characterization of the subsurface
* Geomagnetism, the study of the Earth's magnetic field, including its origin, telluric currents driven by the magnetic field, the Van Allen belts, and the interaction between the magnetosphere and the solar wind. This field is associated with paleomagnetism, or the measurement of the orientation of the Earth's magnetic field over the geologic past.
* Mathematical Geophysics, The development and applications of mathematical methods [2] and techniques for the solution of geophysical problems.[3]
* Geophysical surveying:
* Exploration and engineering geophysics, using surface methods to detect or infer the presence and position of concentrations of ore minerals and hydrocarbons
* Archaeological geophysics, for archaeological imaging or mapping
* Environmental and Engineering Geophysics, for locating underground storage tanks (UST's) or utilities, delineating landfills, locating voids or potential subsidence, finding depth to, P-wave or S-wave velocity of, or rippability of bedrock, or the pathway of groundwater movement
Geophysics
Geophysics,
a major discipline of the Earth sciences and a subdiscipline of physics, is the study of the whole Earth by the quantitative observation of its physical properties. Geophysical data are used in academics to observe tectonic plate motions, study the internal structure of the Earth, supplement data provided by geologic maps, and to nondestructively observe shallow deposits. Geophysical survey data are used to analyze potential petroleum reservoirs and mineral deposits, to locate groundwater, to locate archaeological finds, to find the thicknesses of glaciers and soils, and for environmental remediation. The theories and techniques of geophysics are employed extensively in the planetary sciences in general.
a major discipline of the Earth sciences and a subdiscipline of physics, is the study of the whole Earth by the quantitative observation of its physical properties. Geophysical data are used in academics to observe tectonic plate motions, study the internal structure of the Earth, supplement data provided by geologic maps, and to nondestructively observe shallow deposits. Geophysical survey data are used to analyze potential petroleum reservoirs and mineral deposits, to locate groundwater, to locate archaeological finds, to find the thicknesses of glaciers and soils, and for environmental remediation. The theories and techniques of geophysics are employed extensively in the planetary sciences in general.
Geochemistry
Geochemistry
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and their interaction with the hydrosphere and the atmosphere.
The most important fields of geochemistry are:
1. Isotope geochemistry:Determination of the relative and absolute concentrations of the elements and their isotopes in the earth and on earth's surface.
2. Examination of the distribution and movements of elements in different parts of the earth (crust, mantle, hydrosphere etc.) and in minerals with the goal to determine the underlying system of distribution and movement.
3. Cosmochemistry: Analysis of the distribution of elements and their isotopes in the cosmos.
4. Biogeochemistry: Field of study focusing on the effect of life on the chemistry of the earth.
5. Organic geochemistry: A study of the role of processes and compounds that are derived from living or once-living organisms.
6. Regional, environmental and exploration geochemistry: Applications to environmental, hydrological and mineral exploration studies.
Victor Goldschmidt is considered by most to be the father of modern geochemistry and the ideas of the subject were formed by him in a series of publications from 1922 under the title ‘Geochemische Verteilungsgesetze der Elemente’.
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and their interaction with the hydrosphere and the atmosphere.
The most important fields of geochemistry are:
1. Isotope geochemistry:Determination of the relative and absolute concentrations of the elements and their isotopes in the earth and on earth's surface.
2. Examination of the distribution and movements of elements in different parts of the earth (crust, mantle, hydrosphere etc.) and in minerals with the goal to determine the underlying system of distribution and movement.
3. Cosmochemistry: Analysis of the distribution of elements and their isotopes in the cosmos.
4. Biogeochemistry: Field of study focusing on the effect of life on the chemistry of the earth.
5. Organic geochemistry: A study of the role of processes and compounds that are derived from living or once-living organisms.
6. Regional, environmental and exploration geochemistry: Applications to environmental, hydrological and mineral exploration studies.
Victor Goldschmidt is considered by most to be the father of modern geochemistry and the ideas of the subject were formed by him in a series of publications from 1922 under the title ‘Geochemische Verteilungsgesetze der Elemente’.
Further Branches Of Petrology
Branches
There are three branches of petrology, corresponding to the three types of rocks: igneous, metamorphic, and sedimentary, and another dealing with experimental techniques:
* Igneous petrology focuses on the composition and texture of igneous rocks (rocks such as granite or basalt which have crystallized from molten rock or magma). Igneous rocks include volcanic and plutonic rocks.
* Sedimentary petrology focuses on the composition and texture of sedimentary rocks (rocks such as sandstone, shale, or limestone which consist of pieces or particles derived from other rocks or biological or chemical deposits, and are usually bound together in a matrix of finer material).
* Metamorphic petrology focuses on the composition and texture of metamorphic rocks (rocks such as slate, marble, gneiss, or schist which started out as sedimentary or igneous rocks but which have undergone chemical, mineralogical or textural changes due to extremes of pressure, temperature or both)
* Experimental petrology employs high-pressure, high-temperature apparatus to investigate the geochemistry and phase relations of natural or synthetic materials at elevated pressures and temperatures. Experiments are particularly useful for investigating rocks of the lower crust and upper mantle that rarely survive the journey to the surface in pristine condition. The work of experimental petrologists has laid a foundation on which modern understanding of igneous and metamorphic processes has been built.
There are three branches of petrology, corresponding to the three types of rocks: igneous, metamorphic, and sedimentary, and another dealing with experimental techniques:
* Igneous petrology focuses on the composition and texture of igneous rocks (rocks such as granite or basalt which have crystallized from molten rock or magma). Igneous rocks include volcanic and plutonic rocks.
* Sedimentary petrology focuses on the composition and texture of sedimentary rocks (rocks such as sandstone, shale, or limestone which consist of pieces or particles derived from other rocks or biological or chemical deposits, and are usually bound together in a matrix of finer material).
* Metamorphic petrology focuses on the composition and texture of metamorphic rocks (rocks such as slate, marble, gneiss, or schist which started out as sedimentary or igneous rocks but which have undergone chemical, mineralogical or textural changes due to extremes of pressure, temperature or both)
* Experimental petrology employs high-pressure, high-temperature apparatus to investigate the geochemistry and phase relations of natural or synthetic materials at elevated pressures and temperatures. Experiments are particularly useful for investigating rocks of the lower crust and upper mantle that rarely survive the journey to the surface in pristine condition. The work of experimental petrologists has laid a foundation on which modern understanding of igneous and metamorphic processes has been built.
Branch Of Geology
Petrology (from Greek: πέτρα, petra, rock; and λόγος, logos, knowledge) is the branch of geology that studies rocks, and the conditions in which rocks form.
Lithology once was approximately synonymous with petrography, but in current usage, lithology is a subdivision of petrology focusing on macroscopic hand-sample or outcrop-scale description of rocks, while petrography is the speciality that deals with microscopic details.
In the oil industry, lithology, or more specifically mud logging, is the graphic representation of geological formations being drilled through, and drawn on a log called a mud log. As the cuttings are circulated out of the borehole they are sampled, examined (typically under a 10x microscope) and tested chemically when needed.
Lithology once was approximately synonymous with petrography, but in current usage, lithology is a subdivision of petrology focusing on macroscopic hand-sample or outcrop-scale description of rocks, while petrography is the speciality that deals with microscopic details.
In the oil industry, lithology, or more specifically mud logging, is the graphic representation of geological formations being drilled through, and drawn on a log called a mud log. As the cuttings are circulated out of the borehole they are sampled, examined (typically under a 10x microscope) and tested chemically when needed.
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