Depression (geology)

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. 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.[1]
  • 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.[2]
  • A depression may be an area of subsidence caused by the collapse of an underlying structure. Examples include sinkholes above caves in karst topography, or calderas.[3] 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.
  • A valley is a type of depression usually carved by erosion.
  • 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) of oceanic crust beneath either other oceanic crust or continental crust.
  • 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.[4] Further from the ice, a forebulge may form, which is curved slightly upward.[5]
  • 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.

References

Citations

1. ^ Dictionary of Geologic Terms - B. geotech.org. Retrieved on 2006-08-25.
2. ^ Dictionary of Geologic Terms - K. geotech.org. Retrieved on 2006-08-26.
3. ^ Dictionary of Geologic Terms - C. geotech.org. Retrieved on 2006-08-25.
4. ^ 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).
5. ^ 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).
Oceanic crust      0-20 Ma
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A landform comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography.
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Tectonics, (from the Greek for "builder", tekton), is a field of study within geology concerned generally with the structures within the crust of the Earth (or other planets) and particularly with the forces and movements that have operated in a region to create these
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syncline is a downward-curving fold, with layers that dip toward the center of the structure. On a geologic map, synclines are recognized by a sequence of rock layers that grow progressively younger, followed by the youngest layer at the fold's center or hinge
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A structural basin is a large-scale structural formation of rock strata formed by tectonic warping of previously flat lying strata. Structural basins are geological depressions, and are the inverse of domes. Some elongated structural basins are also known as synclines.
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Sedimentology encompasses the study of modern sediments and understanding the processes that deposit them. It also compares these observations to studies of ancient sedimentary rocks.
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The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification.
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Blowouts are sandy depressions in a sand dune ecosystem (psammosere) caused by the removal of sediments by wind.

Blowouts occur in partially vegetated dunefields including continental dunes as well as coastal dunes.
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WIND (SOLARWIND) was a NASA spacecraft launched on November 1, 1994. It was deployed to study radio and plasma that occur in solar wind, in the Earth's magnetosphere. The spacecraft's original mission was to orbit the Sun at the L1
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Erosion is displacement of solids (soil, mud, rock and other particles) usually by the agents of currents such as, wind, water, or ice by downward or down-slope movement in response to gravity or by living organisms (in the case of bioerosion).
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desert is a landscape form or region that receives very little precipitation. Deserts are defined as areas that receive an average annual precipitation of less than 250 mm (10 in). In the Köppen climate classification system, deserts are classed as (BW).
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Sand is a granular material made up of fine mineral particles. It is a naturally occurring, finely divided rock.

Sand comprises particles, or granules, ranging in diameter from 0.0625 (or 116 mm) to 2 millimeters.
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loess, from the German Löss or Löß, and ultimately from Swiss German lösch (loose), pronounced in several different ways in English (IPA: [ləs, lʌs, lʌrs, lo.
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graben is a depressed block of land bordered by parallel faults. Graben is German for ditch.

A graben is the result of a block of land being downthrown producing a valley with a distinct scarp on each side. Grabens often occur side-by-side with horsts.
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rift is a place where the Earth's crust and lithosphere are being pulled apart. Typical features are a central linear downdropped fault segment, called a graben, with parallel normal faulting and rift-flank uplifts on either side forming a rift valley.
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impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with larger body. In most common usage, the term is used for the approximately circular depression in the surface of a planet, moon or other solid body in the
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A meteorite is a natural object originating in outer space that survives an impact with the Earth's surface without being destroyed. While in space it is called a meteoroid.
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Please [improve the article] or discuss this issue on the talk page. This article has been tagged since September 2007.
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glacier is a large, slow moving river of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity. Glacier ice is the largest reservoir of fresh water on Earth, and second only to oceans as the largest reservoir of total water.
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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.
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Karst topography is a landscape shaped by the dissolution of a soluble layer or layers of bedrock, usually carbonate rock such as limestone or dolomite. These landscapes display distinctive surface features and underground drainages, and in some examples there may be little or no
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caldera is a volcanic feature formed by the collapse of land following a volcanic eruption. They are often confused with volcanic craters. The word 'caldera' comes from the Spanish language, meaning "cauldron".
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maar is a broad, low relief crater that is caused by a phreatic eruption or explosion caused by groundwater contact with hot lava or magma. The maar typically fills with water to form a relatively shallow crater lake.
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subduction zone is an area on Earth where two tectonic plates meet and move towards one another, with one sliding underneath the other and moving down into the mantle, at rates typically measured in centimeters per year.
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volcanic arc is chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma. There are two types of volcanic arcs: oceanic arcs (commonly called island arcs
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The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification.
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Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. Sedimentation is the deposition by settling of a suspended material.
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Volcano:
1. Large magma chamber
2. Bedrock
3. Conduit (pipe)
4. Base
5. Sill
6. Branch pipe
7. Layers of ash emitted by the volcano
8. Flank 9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14.
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geology, a valley is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.

The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys.
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