Depression (geology)

From Wikipedia, the free encyclopedia

Depression in geology is a landform sunken or depressed below the surrounding area. Depressions may be formed by various mechanisms, and may be referred to by a variety of technical terms.

A basin may be any large sediment filled depression.<ref name="UCMPbasin">Collins, Allen; Whitney, Colleen; et al (2006-08-25). Geology - basin. UCMP Glossary. University of California, Berkeley. Retrieved on 2006-08-25.</ref> In tectonics, it may refer specifically to a circular, syncline-like depression: a geologic basin; while in sedimentology, it may refer to an area thickly filled with sediment: sedimentary basin.<ref name="GTb">Dictionary of Geologic Terms - B. geotech.org. Retrieved on 2006-08-25.</ref>

A blowout is a depression created by wind erosion typically in either a desert sand or dry soil (such as a post-glacial loess environment).<ref name="GTb" />

A graben is a down dropped and typically linear depression or basin created by rifting in a region under tensional tectonic forces.

An impact crater is a depression created by an impact such as a meteorite crater.

A kettle is left behind when a piece of ice left behind in glacial deposits melts.<ref name="GTk">Dictionary of Geologic Terms - K. geotech.org. Retrieved on 2006-08-26.</ref>

A depression may be an area of subsidence caused by the collapse of an underlying structure. Examples include sinkholes above caves<ref name="UCMPsinkhole">Collins, Allen; Whitney, Colleen; et al (2006-08-25). Geology - sinkhole. UCMP Glossary. University of California, Berkeley. Retrieved on 2006-08-25.</ref> in karst topography, or calderas<ref name="UCMPcaldera">Collins, Allen; Whitney, Colleen; et al (2006-08-25). Geology - caldera. UCMP Glossary. University of California, Berkeley. Retrieved on 2006-08-25.</ref><ref name="GTc">Dictionary of Geologic Terms - C. geotech.org. Retrieved on 2006-08-25.</ref> or maars in volcanic areas.

A depression may be a region of tectonic downwarping typically associated with a subduction zone and island arc. Fore-arc and back-arc sedimentary basins fill with sediment from an adjacent island arc, or from continental volcanism and uplift.

An oceanic trench is a deep depression with steep sides located in the ocean floor. Oceanic trenches are caused by the subduction (when one tectonic plate is pushed underneath another)<ref name="UCMPsubduction">Collins, Allen; Whitney, Colleen; et al (2006-08-25). Geology - subduction. UCMP Glossary. University of California, Berkeley. Retrieved on 2006-08-25.</ref> of oceanic crust beneath either other oceanic crust or continental crust.<ref name="UCMPoceanictrench">Collins, Allen; Whitney, Colleen; et al (2006-08-25). Geology - oceanic trench. UCMP Glossary. University of California, Berkeley. Retrieved on 2006-08-25.</ref>

A depression may result from the weight of overlying material such as an ice sheet during continental glaciation which is subsequently removed resulting in a basin which slowly rebounds. The area around the ice sheet, though not covered in ice itself, may also be pulled down by the weight of the ice sheet, which is known as peripheral depression.<ref name="MSUperipheraldepression">Glossary of Important Terms in Glacial Geology - Peripheral Depression. Montana State University (1999). Retrieved on 2006-08-25. Cites American Geological Institute’s Glossary of Geology (3rd edition, revised in 1987).</ref> Further from the ice, a forebulge may form, which is curved slightly upward.<ref name="MSUforebulge">Glossary of Important Terms in Glacial Geology - Forebulge. Montana State University (1999). Retrieved on 2006-08-25. Cites American Geological Institute’s Glossary of Geology (3rd edition, revised in 1987).</ref>

A depression may be a pothole - either a simple roadway depression or a fluvial erosional depression in a river streambed, or area affected by coastal water currents.

One of many impressive depressions is the Great Rift Valley of East Africa. Perhaps even more impressive is the Atlantic Ocean basin.

[edit] References

Collins, Allen; Whitney, Colleen; et al (2006-08-25). Geology. UCMP Glossary. University of California, Berkeley. Retrieved on 2006-08-25.
Dictionary of Geologic Terms. geotech.org. Retrieved on 2006-08-25.
Glossary of Important Terms in Glacial Geology. Montana State University (1999). Retrieved on 2006-08-25. Cites American Geological Institute’s Glossary of Geology (3rd edition, revised in 1987).