Where results make sense

About us   |   Why use us?   |   Reviews   |   PR   |   Contact us

Subsidence - Wikipedia, the free encyclopedia 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. en.wikipedia.org /wiki/Subsidence   (745 words)

Subsidence 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. www.tulane.edu /~sanelson/geol204/subsidence.htm   (3304 words)

subsidence. The Columbia Encyclopedia, Sixth Edition. 2001-05 Natural subsidence may occur when limestone, which is easily carved by underground water, collapses, leaving sink holes on the surface, such as in Florida. By 1962 the center of the oil field had subsided slightly over 27 ft (8.5 m), caused by the removal of fluid from the pore spaces in the underground rock, allowing the grains to compact. Subsidence is also caused by the collapse of underground salt, ore, and coal mines. www.bartleby.com /65/su/subsiden.html   (313 words)

Land Subsidence Subsidence and earth fissures are geological events that are accelerated by man through a long-term extraction of groundwater, and they represent a disruption of a natural equilibrium. Subsidence and fissures were at one time perceived to be strictly agricultural problems, the consequences of an areas' extensive use of groundwater. Subsidence predictions were worked out for the aqueduct route for the 50-year period ending in the year 2035, and range from four inches to over 15 feet on the Salt-Gila Aqueduct and from about two feet to almost eight feet on the Tucson Aqueduct. ag.arizona.edu /AZWATER/arroyo/062land.html   (5149 words)

Subsidence   (Site not responding. Last check: 2007-11-07) To get a feel for whether the subsidence caused by this load would be significant, we assume the load was deposited at a constant rate over the last 100 years and we further assume that the sediment was all deposited in an area of 100 km². Ground subsidence is expected to result from the subsequent compaction of the aquifer. We would expect to see a larger subsidence in the GPS data near areas of maximum water withdrawal as opposed to areas distant from pumping stations. www.ngs.noaa.gov /GRD/GPS/Projects/CB/SUBSIDENCE/subsidence.html   (359 words)

GeoFacts No. 12, Mine Subsidence   (Site not responding. Last check: 2007-11-07) Mine subsidence in March 1995 caused a portion of the eastbound lane of Interstate Route 70 (I-70) in Guernsey County to collapse. Subsidence, in the context of underground mining, is the lowering of the Earth's surface due to collapse of bedrock and unconsolidated materials (sand, gravel, silt, and clay) into underground mined areas. The potential area of subsidence is equal to the extraction area plus an area surrounding the extraction area measured by an angle up to 35°, called the angle of draw, from the vertical at the edge of the extraction area. www.dnr.state.oh.us /geosurvey/geo_fact/geo_f12.htm   (1810 words)

Subsidence Background: Mine Subsidence Technological Society Generally, the subsidence theories used to answer these questions are based on the assumption extraction of coal has been completed and a continuous unsupported void has been created. After cessation of mining, subsidence may continue to occur in a steady, gradual manner, or it may stop for a period, to be followed by failure at some later date. Subsidence hazard zones are those areas where ground subsidence may occur as a result of past mining activities. www.mstsociety.org /info/subs/coalSubs.html   (397 words)

Protecting our Ports and Harbors Subsidence Subsidence is the lowering of a portion of the earth's crust, which causes a loss of surface elevation due to the removal of subsurface support. Natural factors contributing to subsidence occurrences are earthquakes, soil compaction, and watering of loess (wind) deposits. Subsidence of up to 2 meters (6.5 feet) could be common during a subduction zone earthquake along certain portions of the Washington and Oregon coasts. www.csc.noaa.gov /products/tsunamis/htm/cascadia/sub_intro.htm   (249 words)

Subsidence crater - Wikipedia, the free encyclopedia A subsidence crater is a hole or depression left on the surface of an area which has had an underground (usually nuclear) explosion. Subsidence craters are created as the "roof" of the cavity caused by the explosion collapses. Subsidence craters in the southern section of the Nevada Test Site. en.wikipedia.org /wiki/Subsidence_crater   (200 words)

Man-made Subsidence Subsidence in the Wilmington oil field caused a great deal of damage because it was in the center of a busy port and industrial area, and it can be used to demonstrate the problem most effectively. Maximum subsidence was 5 feet by 1925, and overall the area affected was close to 4 square miles, corresponding in area and shape with the area that contained the producing oil wells. The subsidence of the field caused faults to develop round its edges, and boundary faults 12-16 inches in offset developed along the north and south edges of the field as it sank. www.geology.ucdavis.edu /~cowen/~GEL115/115CHXXsubsidence.html   (5875 words)

3-D Seismic Tomographic Imaging for Abandoned Mine Subsidence Characterization : Case Histories - Geotechnical Hazards ... Trough subsidence results from a widespread collapse of mine workings, and can be caused by a combination of roof caving, pillar failure, and punching of pillars into soft mine floor. Sinkhole subsidence is associated with the failure of isolated areas or individual openings and is caused by roof failure migrating upward through weak overburden. Based on field studies of sinkhole subsidence previously performed in Boulder County (Matheson, 1987), the expected extent of the rubble zone and angle of draw were superimposed on the tomography results and related to the planned location and bearing horizon of the bridge caissons. www.fhwa.dot.gov /engineering/geotech/hazards/mine/workshops/iawkshp/haramy.cfm   (1565 words)

Land Subsidence in the United States Fact Sheet Land subsidence is a gradual settling or sudden sinking of the Earth's surface owing to subsurface movement of earth materials. Two case studies of organic-soil subsidence focus on examples of rapid subsidence (1 to 3 inches/year) caused by decomposition of the remains of shallow-water sedges and reeds. The occurrence of land subsidence is seldom as obvious as it is in the case of catastrophic sinkholes or mine collapses. water.usgs.gov /ogw/pubs/fs00165   (2041 words)

Subsidence   (Site not responding. Last check: 2007-11-07) Subsidence is caused when the clay beds between the sand and gravel aquifer layers are compressed by forces exerted on the aquifer system during groundwater extraction. It is a common misconception that subsidence causes aquifers to collapse, or that it destroys aquifers. Subsidence is monitored by repeated land surveys and by use of scientific instruments called extensometers. www.nd.water.ca.gov /PPAs/Subsidence/index.cfm   (274 words)

Land subsidence   (Site not responding. Last check: 2007-11-07) Land subsidence is a settling of the Earth's surface due to the compaction of subsurface materials. Subsidence is costly, as it can lead to flooding that damages properties and infrastructure, and saltwater intrusion that degrades groundwater quality. A major component of the district's conjunctive use program is recharging the groundwater basin to replenish the groundwater that is withdrawn. www.valleywater.org /Water/Where_Your_Water_Comes_From/Local_Water/Groundwater/Subsidence.shtm   (227 words)

Harris-Galveston Subsidence District   (Site not responding. Last check: 2007-11-07) It was in the early 1900’s that the Houston area began to see the first true signs of human-induced land subsidence -- initially attributed to the extraction of oil and gas from beneath the surface, and relegated to the land immediately in and around the center of the oil fields. But as subsidence was stabilizing in the coastal areas, groundwater levels in inland areas north and west of Houston were rapidly declining. As a result of the increasing threat subsidence posed to these areas, the HGSD adopted a series of regulatory plans to reduce groundwater pumpage, and ultimately mandated, in their 1999 plan, a reduction to only 20% reliance on groundwater by 2030. www.subsidence.org /history/History_index.html   (1063 words)

Las Vegas Valley: Land Subsidence and Fissuring Due to Ground-Water Withdrawal This subsidence and its relations to specific wells and faults have been very well documented by leveling studies conducted along survey lines, some of which were initially established in 1935 during studies related to the construction of Hoover Dam (Lake Mead). Subsidence in Las Vegas Valley has been monitored since 1935 when the U.S. Coast and Geodetic Survey established a first-order vertical-control network across the valley as a regional monitoring program to document the effects of loading of water impounded in Lake Mead behind Hoover Dam. Subsidence induced by ground-water withdrawal has continued in Las Vegas Valley since about 1935 and presently is as much as 2 m in the center of the valley. geochange.er.usgs.gov /sw/impacts/hydrology/vegas_gw   (2125 words)

SUBSIDENCE Deep subsidence is the slow downward movement of land caused by Hydrocompaction is notable not for the magnitude of the subsidence that Hydrocompaction is the subsidence of shallow soils and sediments as a www.uwsp.edu /geo/faculty/ozsvath/LECTURES/Subsidence.htm   (411 words)

HighBeam Encyclopedia - subsidence SUBSIDENCE [subsidence] lowering of a portion of the earth's crust. For example, withdrawal of oil from the field at Long Beach, California, beginning in 1936 resulted in subsidence at rates ranging from 0.5 to 2.0 ft (0.15-0.61 m) per yr in the center of the field. In a 2003 book, he warned of the hazards of coastal subsidence and predicted that the New Orleans levees would be breached. www.encyclopedia.com /html/s1/subsiden.asp   (533 words)

Coal Mine Subsidence Theory The sag is propagated upward to the surface, and, it follows, that the maximum surface subsidence can be no greater than the thickness of the coal bed mined. The purpose of the Subsidence Hazard Map is to represent those areas where the land surface may possibly be affected by subsidence or collapse related to underground or surface mining of coal and clay. The subsidence hazard zone boundary on the hanging wall side of the mine will lie beyond the mapped workings a distance equal to the maximum depth of the mine plus a 100’ safety zone. www.mines.edu /fs_home/tboyd/Coal/sub_theory   (781 words)

Analysis of the Subsidence and Water-Management Issues of the Santa Clara Valley, California   (Site not responding. Last check: 2007-11-07) This constraint on subsidence may be too restrictive and requires additional evaluation on the basis of new subsidence data. Important regional subsidence concerns include regional compaction and subsidence that may cause damage to man-made structures, reduce long-term yield to wells, and permanently alter natural and man-made surface drainage networks that results in potential flooding or lack of drainage. The problem remains that the existing subsidence and ground-water flow are very complex and are not completely understood and the existing monitoring and modeling tools need to be upgraded and updated to provide water managers with a mechanism to physically address the water-management issues. ca.water.usgs.gov /projects00/ca554.html   (3277 words)

FS-051-00--Measuring Land Subsidence from Space Subsidence in the United States has directly affected more than 17,000 square miles in 45 states, and associated annual costs are estimated to be approximately $125 million. The principal causes of subsidence are aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost (National Research Council, 1991). The InSAR derived displacements are consistent with historical patterns of subsidence and vertical displacements measured in deepseated borehole extensometers in Sunnyvale and San Jose. pubs.usgs.gov /fs/fs-051-00   (1785 words)

Subsidence in Jefferson County It is possible to map the subsidence which has occurred in the past and to estimate the extent of the subsidence potential which exists today. This type of subsidence is the most common of all and is particularly prevalent on the east side of the Dakota hogback from the I-70 highway cut, north to Coal Creek Canyon. Their origin is believed to be due to subsidence over old coal mine stopes because they are located over the mapped mine location and because they overlie the trend of the basal Laramie. www.mines.edu /fs_home/tboyd/Coal/sub_jeffco   (1161 words)

Rapid subsidence over oil fields measured by SAR interferometry More rapid subsidence of the ground surface is usually attributable to human activities, such as the extraction of fluids from beneath the surface. A subsidence bowl forms at the surface [Bondor and de Rouffignac, 1995; Holzer and Bluntzer, 1984; Martin and Serdengecti, 1984]. Subsidence at the South Belridge field was first noted in the 1980's [Bondor and de Rouffignac, 1995; Bowersox and Shore, 1990]. www-radar.jpl.nasa.gov /s323/IntSARapps/LH-Belridge_GRL.html   (2587 words)

Yolo Subsidence Monitoring Project Subsidence is generally caused by fluid withdrawal or hydro-compaction. Subsidence is not a phenomenon that lends itself to prediction (of annual rates, for example), except in an average sense, since it is a function of several variables that vary from year to year and even from season to season. Subsidence could place previously unaffected properties in the flood plain, and could similarly result in the removal of some currently affected areas from requiring flood plain insurance. www.yarn.org /subsidence/about.html   (3700 words)

Marshalls Chartered Surveyors - Subsidence   (Site not responding. Last check: 2007-11-07) A chartered surveyor will be able to work out whether or not there is subsidence and what the likely cause is. If diagnosis is not straightforward, they may recommend you bring in a structural engineer to give a second opinion. In most cases the first signs of a problem are visible cracks in a particular area of the house, and these will need to be measured and monitored, perhaps for as long as 12 months. Solving subsidence can be a lengthy process which can take up to two years. s104304524.websitehome.co.uk /subsidence.htm   (695 words)

Subsidence and Fault Activation Related to Fluid Energy Production, Gulf Coast Basin Project The lowered pressures (3) increase the effective stress of the overburden (4), which causes compaction of the reservoir rocks and may cause formerly active faults (1) to be reactivated (5). Where subsidence and fault reactivation occur in wetland areas, the wetlands typically are submerged and changed to open water (7). The Gulf Coast Basin is a region where subsidence and fault activation are common around large, mature oil and gas fields even though moderately deep hydrocarbon production has generally been disregarded as the primary cause. coastal.er.usgs.gov /gc-subsidence   (314 words)

INSAR-Land Surface Subsidence   (Site not responding. Last check: 2007-11-07) Subsidence in the greater Houston area has been identified as a contributor to loss of wetlands, increased shoreline erosion and conversion of freshwater marshes to brackish and saline marshes around the Galveston Bay system. Subsidence has resulted from subsurface liquid withdrawal, primarily groundwater, and in some areas measured at more than twelve feet. The greater Houston area, with its subsidence studies program and networks of traditional measuring systems, provides an ideal standard and relevant opportunity to evaluate the INSAR technology for monitoring land subsidence in a humid coastal environment. www.fws.gov /texascoastalprogram/insar.htm   (287 words)

Try your search on: Qwika (all wikis)

About us   |   Why use us?   |   Reviews   |   Press   |   Contact us   Copyright © 2005-2007 www.factbites.com Usage implies agreement with terms.