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Encyclopedia > Subsidence
A road destroyed by subsidence and shear.

In geology, engineering, and surveying, subsidence is the motion of a surface (usually, the Earth's surface) as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation. In meteorology, subsidence refers to the downward movement of air. Download high resolution version (948x622, 131 KB)A section of the A6187, near Castleton, UK, destroyed by geological subsidence. ... Download high resolution version (948x622, 131 KB)A section of the A6187, near Castleton, UK, destroyed by geological subsidence. ... Mountain road with hairpin turns in the French Alps For other uses, see Road (disambiguation). ... Shear stress is a stress state where the stress is parallel or tangential to a face of the material, as opposed to normal stress when the stress is perpendicular to the face. ... This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... Engineering is the design, analysis, and/or construction of works for practical purposes. ... Surveyor at work with a leveling instrument. ... It has been suggested that this article or section be merged with Geodetic system. ... A tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. ... Satellite image of Hurricane Hugo with a polar low visible at the top of the image. ...

Contents

Surfaces

There are several types of subsidence, listed below in order of increasing scale:


Subsidence by dissolution of limestone

Subsidence frequently occurs in karst terrains, where dissolution of limestone by fluid flow in the subsurface causes the creation of voids (i.e. caves). If the roof of these voids becomes too weak, it can collapse and the overlying rock and earth will fall into the space, causing subsidence at the surface. This type of subsidence can result in sinkholes which can be many hundreds of meters deep and can provide areas of ecological isolation which see the evolution of new branches of animal and plant life. Karst topography occurs when a landscape is marked by underground drainage patterns. ...


Mining-induced subsidence

Several types of sub-surface mining, and specifically methods which intentionally cause the extracted void to collapse (such as pillar extraction, longwall mining and any metalliferous mining method which utilises "caving" such as "block caving" or "sub-level caving") will result in surface subsidence. Mining induced subsidence is relatively predictable in its magnitude, manifestation and extent, except where a sudden pillar or near-surface underground tunnel collapse occurs (usually very old workings). Mining induced subsidence is nearly always very localised to the surface above the mined area, plus a margin around the outside [1]. The vertical magnitude of the subsidence itself typically does not cause problems, except in the case of drainage (including natural drainage) - rather it is the associated surface compressive and tensile strains, curvature, tilts and horizontal displacement that are the cause of the worst damage to the natural environment, buildings and infrastructure. Where mining activity is planned, mining-induced subsidence can be successfully managed if there is co-operation from all of the stakeholders [2]. This is accomplished through a combination of careful mine planning, the taking of preventative measures, and the carrying out of repairs post-mining. Sub-surface mining or underground mining refers to a group of techniques used for the extraction of valuable minerals or other geological materials from the earth. ... Longwall mining is form of underground coal mining. ... Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals such as those containing metals like gold, copper, zinc, nickel and lead or gems such as diamonds. ...


Subsidence by faulting

When differential stresses exist in the Earth, these can be accommodated either by geological faulting in the brittle crust, or by ductile flow in the hotter and more fluid mantle. Where faults occur, absolute subsidence may occur in the footwall of normal faults. In reverse, or thrust, faults, relative subsidence may be measured in the hangingwall. Geologic faults, fault lines or simply faults are planar rock fractures, which show evidence of relative movement. ... Earth cutaway from core to exosphere. ... Ductility is the physical property of being capable of sustaining large plastic deformations without fracture (in metals, such as being drawn into a wire). ... Earth cutaway from core to exosphere. ... Geologic faults, fault lines or simply faults are planar rock fractures, which show evidence of relative movement. ... Geologic faults, fault lines or simply faults are planar rock fractures, which show evidence of relative movement. ...


Subsidence by isostatic rebound

The crust floats buoyantly in the plastic asthenosphere, with a ratio of mass below the "surface" in proportion to its own density and the density of the asthenosphere. If mass is added to the crust (e.g. through deposition), the crust is thought to subside minisculely to compensate and maintain isostatic balance. Earth cutaway from core to exosphere. ... Earth cutaway from core to exosphere. ... Deposition is a word used in many fields to describe different processes: In law, deposition is the taking of testimony outside of court. ... Isostasy is a term used in Geology to refer to the state of ice above stasy and is angravitational equilibrium between the Earths lithosphere and asthenosphere such that the tectonic plates float at an elevation which depends on their thickness and density. ...


Subsidence caused by extraction of natural gas

If natural gas is extracted from a natural gas field the initial pressure (up to 600 bar) in the field will drop over the years. The gas pressure also supports the soil layers above the field. If the pressure drops, the soil pressure increases and this leads to subsidence at the ground level. Since exploration of the Slochteren (Netherlands) gas field started in the late 1960s the ground level over a 250 km² area has dropped with a current maximum of 30 cm [3]. See also this subsidence lecture. Natural gas is a gaseous fossil fuel consisting primarily of methane but including significant quantities of ethane, butane, propane, carbon dioxide, nitrogen, helium and hydrogen sulfide. ... Natural gas rig Oil and natural gas are produced by the same geological process: anaerobic decay of organic matter deep under the Earths surface. ... The bar (symbol bar) and the millibar (symbol mbar, also mb) are units of pressure. ... Slochteren is a municipality in the northeastern Netherlands. ... The 1960s decade refers to the years from January 1, 1960 to December 31, 1969, inclusive. ...


This type of subsidence can similarly be caused by extraction of other resources, e.g. ground water, petroleum or rock salt. Groundwater is any water found below the land surface. ... Pumpjack pumping an oil well near Lubbock, Texas Ignacy Łukasiewicz - inventor of the refining of kerosene from crude oil. ... Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with formula NaCl. ...


Subsidence induced by water table management

The habitation of lowlands, such as coastal or delta plains, requires drainage. The resulting aeration of the soil leads to the oxidation of its organic components, such as peat, and this decomposition process may cause significant land subsidence. This applies especially when ground water levels are periodically adapted to subsidence, in order to maintain desired unsaturated zone depths, exposing more and more peat to oxygen. In addition to this, drained soils compact as a result of pore-tension reduction (see compaction). In this way, land subsidence has the potential of becoming self-perpetuating, having rates up to 5 cm/yr. Water management used to be tuned primarily to factors such as crop optimisation but, to varying extents, avoiding subsidence has come to be taken into account as well. In physical geography, a lowland is any broad expanse of land with a general low level. ... The West Coast of New Zealand The coast is defined as the part of the land adjoining or near the ocean. ... Nile River delta, as seen from Earth orbit. ... Drainage is the natural or artificial removal of surface and sub-surface water from a given area. ... Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland Technically, soil forms the pedosphere: the interface between the lithosphere (rocky part of the planet) and the biosphere, atmosphere, and hydrosphere. ... Peat in Lewis, Scotland Peat is an accumulation of partially decayed vegetation matter. ... Groundwater is any water found below the land surface. ... Cross-section of a hillslope depicting the vadose zone, capillary fringe, water table, and phreatic or saturated zone. ... This page is a candidate for speedy deletion. ... LLGHHHHHHHHHK BNMNKBV JKVGKJJH JHVG KJVH KJV KJV JKV JV JV KJFYG KHV KJV gfnnnnnnnnnnhngjkv jh b ... A crop is any plant that is grown in significant quantities to be harvested as food, livestock fodder, or for another economic purpose. ...


Atmosphere

The most common cause of subsidence in the atmosphere is cold temperatures: as air cools, it becomes more dense and moves towards the ground, just as warm air becomes less dense and moves upwards. Subsidence generally causes high barometric pressure as more air moves into the same space: the polar highs are areas of almost constant subsidence, as are the horse latitudes, and these areas of subsidence are the sources of much of the world's prevailing wind. Subsidence also causes many smaller-scale weather phenomena, such as morning fog. An extreme form of subsidence is a downburst, which can result in damage similar to that produced by a tornado. A milder form of subsidence is referred to as downdraft. Layers of Atmosphere - not to scale (NOAA)[3] Earths atmosphere is a layer of gases surrounding the planet Earth and retained by the Earths gravity. ... Atmospheric pressure is the pressure caused by the weight of air above any area in the Earths atmosphere. ... The polar highs are areas of high atmospheric pressure around the north and south poles. ... Horse latitudes or Subtropical High are subtropical latitudes between 30 and 35 degrees both north and south, characterized by light winds and hot, dry weather, caused by descending air. ... Wind is the quasi-horizontal movement of air (as opposed to an air current) caused by a horizontal pressure gradient force. ... Weather is a term that encompasses phenomena in the atmosphere of a planet. ... The curl phase soon after an intense microburst impacted the surface Downburst damages in a straight line. ... A downdraft is downward moving air, usually the direct result of air convection within the thunderstorm. ...


See also


  Results from FactBites:
 
Subsidence - Wikipedia, the free encyclopedia (745 words)
This type of subsidence can result in sinkholes which can be many hundreds of metres deep and can provide areas of ecological isolation which see the evolution of new branches of animal and plant.
The most common cause of subsidence in the atmosphere is cold temperatures: as air cools, it becomes more dense and moves towards the ground, just as warm air becomes less dense and moves upwards.
Subsidence generally causes high barometric pressure as more air moves into the same space: the polar highs are areas of almost constant subsidence, as are the horse latitudes, and these areas of subsidence are the sources of much of the world's prevailing wind.
Subsidence (3304 words)
Subsidence hazards involve either the sudden collapse of the ground to form a depression or the slow subsidence or compaction of the sediments near the Earth's surface.
In such settings, subsidence is a natural process Sediments deposited by the rivers and oceans get buried, and the weight of the overlying, newly deposited sediment, compacts the sediment and the material subsides.
Where fluid withdrawal is the main cause of subsidence, information on the rate of fluid withdrawal should be determined and combined with studies of the material in the subsurface based on sampling with drill core methods.
  More results at FactBites »

 
 

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