A road destroyed by subsidence and shear, near Castleton, Derbyshire. A road is an identifiable route, way or path between two or more places. A shear stress, denoted \tau\ ( Tau) is defined as a stress which is applied Parallel or tangential to a face of a material This article is about the English village in Derbyshire For other uses see Castleton. History The area that is now Derbyshire was first visited probably briefly by humans 200000 years ago during the Aveley Interglacial as evidenced by a Middle

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. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit Engineering is the Discipline and Profession of applying technical and scientific Knowledge and Surveying is the technique and science of accurately determining the terrestrial or three-dimensional space Position of points and the distances and angles between This article describes a concept from Surveying and Geodesy. For other meanings see Datum (disambiguation. The opposite of subsidence is uplift, which results in an increase in elevation. Tectonic uplift is a geological process most often caused by Plate tectonics which increases elevation The elevation of a Geographic location is its height above a fixed reference point often the mean sea level. There are several types of subsidence, listed below in order of increasing scale:

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. Karst topography is a landscape shaped by the dissolution of a layer or layers of soluble Bedrock, usually Carbonate rock such as Limestone Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 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.

Mining-induced

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. Longwall mining is a form of underground Coal mining where a long wall (typically about 250-400 m long of coal is mined in a single slice (typically 1-2 m thick Underground hard rock Mining refers to various underground mining techniques used to excavate hard minerals such as those containing metals like Gold, 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.

Faulting induced

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. In Geology a fault, or fault line, is a planar rock fracture which shows evidence of relative movement In Geology, a crust is the outermost solid shell of a planet or moon Ductility is a mechanical property used to describe the extent to which materials can be deformed plastically or "stretched" into "wires" without The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided 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.

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. The asthenosphere (from an invented Greek a + ' sthenos "without strength" and Greek word σφαίρα (sphera meaning globe is the If mass is added to the crust (e. g. through deposition), the crust is thought to subside minisculely to compensate and maintain isostatic balance. Isostasy (Greek isos = "equal" stásis = "standstill" is a term used in Geology to refer to the state of gravitational equilibrium between the

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. Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, Oil and Natural gas are produced by the same geological process anaerobic Decay of Organic matter deep under the Earth's surface The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. 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]. Slochteren ( is a Municipality in the northeastern Netherlands. The Netherlands ( Dutch:, ˈnedərlɑnt is the European part of the Kingdom of the Netherlands, which consists of the Netherlands the Netherlands The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 See also this subsidence lecture.

This type of subsidence can similarly be caused by extraction of other resources, e. g. ground water, petroleum or rock salt. Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations Petroleum ( L petroleum, from Greek πετρέλαιον, lit Halite is the Mineral form of Sodium chloride, Na[[chlorine Cl]] commonly known as rock salt.

Groundwater-related

San Joaquin Valley subsidence

Main article: Groundwater-related subsidence

The habitation of lowlands, such as coastal or delta plains, requires drainage. The San Joaquin Valley (ˌsæn wɑːˈkiːn refers to the area of the Central Valley of California that lies south of the Sacramento-San Joaquin Delta Groundwater-related subsidence is the Subsidence (or the sinking of land resulting from Groundwater extraction In physical Geography, a lowland is any broad expanse of land with a general low level The coast is defined as the part of the land adjoining or near the Ocean. A delta is a Landform where the mouth of a River flows into an Ocean, Sea, Estuary, Lake or another river Drainage is the natural or artificial removal of surface and sub-surface water from a given area 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. Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel Peat is an accumulation of partially Decayed Vegetation matter. 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. The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the phreatic zone or zone of saturation ("vadose" In addition to this, drained soils consolidate as a result of increased effective stress. Consolidation is a process by which Soils decrease in volume It occurs when stress is applied to a soil that causes the soil particles to pack together more tightly Karl von Terzaghi first proposed the relationship for effective stress in 1936 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. Water management is the practices of planning developing distribution and optimum utilizing of water resources under defined water polices and regulations

Seasonal effects

See also: expansive clay

Many soils contain significant proportions of clay which because of the very small particle size are affected by changes in soil moisture content. Expansive clay is a Clay that is prone to large volume changes that are directly related to changes in Water content. Seasonal drying of the soil results in a reduction in soil volume and a lowering of the soil surface. If building foundations are above the level to which the seasonal drying reaches they will move and this can result in damage to the building in the form of tapering cracks. Trees and other vegetation can have a significant local effect on seasonal drying of soils. Over a number of years a cumulative drying occurs as the tree grows, this can lead to the opposite of subsidence, known as heave or swelling of the soil, when the tree declines or is felled. As the cumulative moisture deficit is reversed, over a period which can last as many as 25 years, the surface level around the tree will rise and expand laterally. This is often more damaging to buildings unless the foundations have been strengthened or designed to cope with the effect.