Escarpment

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Escarpment face of a cuesta, broken by a fault, overlooking Trenton, Cloudland Canyon State Park, and Lookout Mountain, in Georgia Cuesta - Lookout Mountain, Georgia.png
Escarpment face of a cuesta, broken by a fault, overlooking Trenton, Cloudland Canyon State Park, and Lookout Mountain, in Georgia

An escarpment, or scarp, is a steep slope or long cliff that forms as an effect of faulting or erosion and separates two relatively level areas having differing elevations. Usually scarp and scarp face are used interchangeably with escarpment.

Cliff A vertical, or near vertical, rock face of substantial height

In geography and geology, a cliff is a vertical, or nearly vertical, rock exposure. Cliffs are formed as erosion landforms by the processes of weathering and erosion. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually formed by rock that is resistant to weathering and erosion. Sedimentary rocks most likely to form cliffs include sandstone, limestone, chalk, and dolomite. Igneous rocks such as granite and basalt also often form cliffs.

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Some sources differentiate the two terms, however, where escarpment refers to the margin between two landforms (while scarp remains synonymous with a cliff or steep slope). [1] [2] In this usage an escarpment is a ridge which has a gentle (dip) slope on one side and a steep scarp slope on the other side.

More loosely, the term scarp also describes a zone between a coastal lowland and a continental plateau which shows a marked, abrupt change in elevation[ citation needed ] caused by coastal erosion at the base of the plateau.

Plateau An area of a highland, usually of relatively flat terrain

In geology and physical geography, a plateau, also called a high plain or a tableland, is an area of a highland, usually consisting of relatively flat terrain, that is raised significantly above the surrounding area, often with one or more sides with steep slopes. Plateaus can be formed by a number of processes, including upwelling of volcanic magma, extrusion of lava, and erosion by water and glaciers. Plateaus are classified according to their surrounding environment as intermontane, piedmont, or continental.

Formation and description

Scarps are generally formed by one of two processes: either by differential erosion of sedimentary rocks, or by movement of the Earth's crust at a geologic fault. The first is the more common type: the escarpment is a transition from one series of sedimentary rocks to another series of a different age and composition. Escarpments are also frequently formed by faults. When a fault displaces the ground surface so that one side is higher than the other, a fault scarp is created. This can occur in dip-slip faults, or when a strike-slip fault brings a piece of high ground adjacent to an area of lower ground.

Erosion Processes which remove soil and rock from one place on the Earths crust, then transport it to another location where it is deposited

In earth science, erosion is the action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, animals, and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolic) erosion, zoogenic erosion, and anthropogenic erosion. The particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by its dissolving into a solvent, followed by the flow away of that solution. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres.

Sedimentary rock Rock formed by the deposition and subsequent cementation of material

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of small particles and subsequent cementation of mineral or organic particles on the floor of oceans or other bodies of water at the Earth's surface. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. Before being deposited, the geological detritus was formed by weathering and erosion from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.

Fault scarp A small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other

A fault scarp is a small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other. It is the topographic expression of faulting attributed to the displacement of the land surface by movement along faults. They are exhibited either by differential movement and subsequent erosion along an old inactive geologic fault, or by a movement on a recent active fault.

Schematic cross section of a cuesta, dip slopes facing left, and harder rocklayers in darker colors than softer ones. Cuesta schematic1.PNG
Schematic cross section of a cuesta, dip slopes facing left, and harder rocklayers in darker colors than softer ones.

Earth is not the only planet where escarpments occur. They are believed to occur on other planets when the crust contracts, as a result of cooling. On other Solar System bodies such as Mercury, Mars, and the Moon, the Latin term rupes is used for an escarpment.

Crust (geology) The outermost solid shell of a rocky planet, dwarf planet, or natural satellite

In geology, the crust is the outermost solid shell of a rocky planet, dwarf planet, or natural satellite. It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase.

Solar System planetary system of the Sun

The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, such as the five dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.

Mercury (planet) Smallest and closest planet to the Sun in the Solar System

Mercury is the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 87.97 days is the shortest of all the planets in the Solar System. It is named after the Roman deity Mercury, the messenger of the gods.

Shaded and colored image from the Shuttle Radar Topography Mission--shows an elevation model of New Zealand's Alpine Fault running about 500 km (300 mi) long. The escarpment is flanked by a chain of hills squeezed between the fault and the mountains of New Zealand's Southern Alps. Northeast is towards the top. Alpine Fault SRTM (vertical).jpg
Shaded and colored image from the Shuttle Radar Topography Mission—shows an elevation model of New Zealand's Alpine Fault running about 500 km (300 mi) long. The escarpment is flanked by a chain of hills squeezed between the fault and the mountains of New Zealand's Southern Alps. Northeast is towards the top.

Erosion

When sedimentary beds are tilted and exposed to the surface, erosion and weathering may occur. Escarpments erode gradually and over geological time. The mélange tendencies of escarpments results in varying contacts between a multitude of rock types. These different rock types weather at different speeds, according to Goldich dissolution series so different stages of deformation can often be seen in the layers where the escarpments have been exposed to the elements.

Weathering Breaking down of rocks, soil and minerals as well as artificial materials through contact with the Earths atmosphere, biota and waters

Weathering is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earth's atmosphere, water, and biological organisms. Weathering occurs in situ, that is, in the same place, with little or no movement, and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity and then being transported and deposited in other locations.

Mélange A large-scale breccia typically consisting of a jumble of large blocks of varied lithologies

In geology, a mélange is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically consists of a jumble of large blocks of varied lithologies. Both tectonic and sedimentary processes can form mélange.

Goldich dissolution series

The Goldich dissolution series is a way of predicting the relative stability or weathering rate of various minerals on the Earth's surface. S. S. Goldich came up with the series in 1938 after studying soil profiles. He found that minerals that form at higher temperatures and pressures are less stable on the surface than minerals that form at lower temperatures and pressures. This pattern follows the same pattern of the Bowen's reaction series, with the minerals that are first to crystallize also the first the undergo chemical weathering.

Significant escarpments

Africa

Antarctica

Asia

Australia and New Zealand

Europe

The Sierra Escarpment in California. SierraEscarpmentCA.jpg
The Sierra Escarpment in California.

North America

At the Florida Escarpment, seen in the eastern Gulf of Mexico, the sea bed drops precipitously from less than 300 to 3,000 m (1,000 to 10,000 ft) over a short distance. Fixed gulf map.png
At the Florida Escarpment, seen in the eastern Gulf of Mexico, the sea bed drops precipitously from less than 300 to 3,000 m (1,000 to 10,000 ft) over a short distance.

South America

See also

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Slump (geology)

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Scarp may refer to:

Mesa Elevated area of land with a flat top and sides that are usually steep cliffs

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North Downs ridge of chalk hills in south east England

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Geology of the United States regional geology

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Ridge A geological feature consisting of a chain of mountains or hills that form a continuous elevated crest for some distance

A ridge or a mountain ridge is a geological feature consisting of a chain of mountains or hills that form a continuous elevated crest for some distance. The sides of the ridge slope away from narrow top on either side.The line along the crest formed by the highest points, with the terrain dropping down on either side, is called the ridgeline. Ridges are usually termed hills or mountains as well, depending on size.

Cuesta A hill or ridge with a gentle slope on one side and a steep slope on the other

A cuesta is a hill or ridge with a gentle slope on one side, and a steep slope on the other. In geology the term is more specifically applied to a ridge where a harder sedimentary rock overlies a softer layer, the whole being tilted somewhat from the horizontal. This results in a long and gentle backslope called a dip slope that conforms with the dip of resistant strata, called caprock. Where erosion has exposed the frontslope of this, a steep slope or escarpment occurs. The resulting terrain may be called scarpland.

Dip slope topographic surface which slopes in the same direction as the dip of the underlying strata

A dip slope is a topographic (geomorphic) surface which slopes in the same direction, and often by the same amount, as the true dip or apparent dip of the underlying strata. A dip slope consists of the upper surface of a resistant layer of rock, often called caprock, that is commonly only slightly lowered and reduced in steepness by erosion. Dip slopes form the backslopes of cuestas, homoclinal ridges, hogbacks, and flatirons. The frontslopes of such ridges consist of either an escarpment, a steep slope, or perhaps even a line of cliffs. Generally, cuestas and homoclinal ridges are asymmetrical in that their dip slopes are less steep than their escarpments. In the case of hogbacks and flatirons, the dip of the rocks is so steep that their dip slope approaches the escarpment in their steepness.

Fault block very large block of rock

Fault blocks are very large blocks of rock, sometimes hundreds of kilometres in extent, created by tectonic and localized stresses in the Earth's crust. Large areas of bedrock are broken up into blocks by faults. Blocks are characterized by relatively uniform lithology. The largest of these fault blocks are called crustal blocks. Large crustal blocks broken off from tectonic plates are called terranes. Those terranes which are the full thickness of the lithosphere are called microplates. Continent-sized blocks are called variously microcontinents, continental ribbons, H-blocks, extensional allochthons and outer highs.

Great Escarpment, Southern Africa Major topographical feature in southern Africa

The Great Escarpment is a major topographical feature in Africa that consists of steep slopes from the high central Southern African plateau downward in the direction of the oceans that surround Southern Africa on three sides. While it lies predominantly within the borders of South Africa, in the east it extends northwards to form the border between Mozambique and Zimbabwe, continuing on beyond the Zambezi River valley to form the Muchinga Escarpment in eastern Zambia. In the west, it continues northwards into Namibia and Angola.

Hogback (geology) A long, narrow ridge or a series of hills with a narrow crest and steep slopes of nearly equal inclination on both flanks

In geology and geomorphology, a hogback or hog's back is a long, narrow ridge or a series of hills with a narrow crest and steep slopes of nearly equal inclination on both flanks. Typically, the term is restricted to a ridge created by the differential erosion of outcropping, steeply dipping, homoclinal, and typically sedimentary strata. One side of a hogback consists of the surface of a steeply dipping rock stratum called a dip slope. The other side is an erosion face that cuts through the dipping strata that comprises the hogback. The name "hogback" comes from the Hog's Back of the North Downs in Surrey, England, which refers to the landform's resemblance in outline to the back of a hog. The term is also sometimes applied to drumlins and, in Maine, to both eskers and ridges known as "horsebacks".

A homoclinal ridge or strike ridge is a hill or ridge with a moderate, generally between 10° to 30°, sloping backslope. Its backslope is a dip slope, that conforms with the dip of a resistant stratum or strata, called caprock. On the other side of the other slope, which is its frontslope, of a homoclinal ridge is a steeper or even cliff-like frontslope (escarpment) that is formed by the outcrop of the caprock. The escarpment cuts through the dipping strata that comprises the homoclinal ridge.

A pediment is a very gently sloping (.5°-7°) inclined bedrock surface. It typically slopes down from the base of a steeper retreating desert cliff, or escarpment, but may continue to exist after the mountain has eroded away. It is caused by erosion. It develops when sheets of running water wash over it in intense rainfall events. It may be thinly covered with fluvial gravel that has washed over it from the foot of mountains produced by cliff retreat erosion. It is typically a concave surface gently sloping away from mountainous desert areas.

Nilokeras Scopulus

Nilokeras Scopulus is a long escarpment (cliff) in the northern hemisphere of the planet Mars. It is located along the southeastern boundary of the Tempe Terra plateau and forms the northern valley wall of the downstream portion of the immense Kasei Valles outflow channel system. The escarpment is 765 km long and ranges from 1 to a little over 2 km (3300–6600 ft) in height.

Scarp retreat

Scarp retreat is a geological process through which the location of an escarpment changes over time. Typically the cliff is undermined, rocks fall and form a talus slope, the talus is chemically or mechanically weathered and then removed through water or wind erosion, and the process of undermining resumes. Scarps may retreat for tens of kilometers in this way over relatively short geological time spans, even in arid locations.

Serra dos Órgãos mountain range in the state of Rio de Janeiro, Brazil

The Serra dos Órgãos is a mountain range in the state of Rio de Janeiro, Brazil. It contains the Serra dos Órgãos National Park.

References

  1. Easterbrook, D. J. (1999) Surface processes and landforms. (Second Ed). Prentice Hall, Upper Saddle River, New Jersey.
  2. Summary: Escarpments, US Army Corps of Engineers.
  3. Lidmar-Bergström (1988). "Denudation surfaces of a shield area in southern Sweden". Geografiska Annaler . 70 A (4): 337–350.