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.
Components of a scarp where the caprock slopes back from the rim, as is commonAerial view of retreating scarp in Namibia.
A scarp is a line of cliffs that has usually been formed by faulting or erosion. If it is protected by a strong caprock, or if it contains vertical fractures, it may retain its steep profile as it retreats.[1] Scarps in dry climates typically have a near-vertical upper face, that may account for 10% - 75% of the total height, with a talus-covered sloping rampart forming the lower section. The caprock is undermined as the rampart and face are eroded, and eventually a section collapses.[1] A strong caprock will typically create a relatively high cliff, since more undermining is needed to cause it to fail.[2] Other factors determining how easily a cliff will fail are the bedding and jointing, direction of dip and thickness of the caprock. A thin caprock will result in low cliffs that retreat quickly.[3]
However, a caprock is not essential for scarp retreat to occur as higher humidity and weathering at the foot ensures erosion at the foot drives (or keeps up with) the erosion of the free face.[4][5]
The most common way in which a scarp retreats is through rockfall, where individual blocks calve from the cliff or large sections of the cliff face collapse at once. In some high-energy situations, much of the rock may be powdered in a rockfall and easily eroded. Generally, though, the fallen debris must be weathered and the rampart eroded before scarp retreat can continue.[6] Mechanical and chemical weathering followed by wind erosion may operate in arid regions, where cliffs may retreat for long distances.[1] In such regions, large areas of shale badlands may be left behind as the scarp retreats.[3] Erosion may be caused by the sea where the scarp runs along a coast, or by streams in humid areas.[1]
Rate of retreatedit
The rate of retreat depends on the types of rock and the factors causing erosion. A study published in 2006 determined that the rate of scarp retreat in the Colorado Plateau today varies from 0.5 to 6.7 kilometres (0.31 to 4.16 mi) per million years depending on the thickness and resistance to erosion of the caprock.[7] Retreat of the Great Escarpment in Australia along the river valleys in the New England region appears to be progressing at about 2 kilometres (1.2 mi) per million years.[8] A study of cuesta scarp retreat in southern Morocco showed an average rate of 1.3 kilometres (0.81 mi) per million years in areas with thin conglomerate caprocks. Where there were thicker, more resistant limestone caprocks the rate of retreat was slower, about 0.5 kilometres (0.31 mi) per million years.[9]
The Colorado Plateau has a cuesta scarp topography, consisting of slightly deformed strata of alternating harder and softer rocks. The climate has been mostly dry throughout the Cenozoic.[7] The conspicuous scarps on the plateau have massive sandstone caps over easily weathered rock such as shale. Freeze-thaw and groundwater sapping contribute to scarp retreat in this region.[10]
The Drakensberg mountains in South Africa are capped by a layer of Karoo basalts about 1,000 metres (3,300 ft) thick, which overlay Clarens formation sandstones. They have long been considered a classic example of a landform created by scarp retreat following continental break-up, with the retreat controlled by an inland drainage divide. However, they have inland-facing scarps as well as seaward-facing scarps, so factors other than continental break-up have contributed to their formation. A 2006 paper argued that surface process models may be inadequate in explaining rates of scarp retreat, which can also be greatly affected by the types of rock encountered as the scarp retreats, and by other factors such as climate, tectonic processes and possibly plant cover.[11]
Johnson, David (2009-11-04). The Geology of Australia. Cambridge University Press. p. 202. ISBN978-0-521-76741-5. Retrieved 2012-11-29.
Moore, Andy; Blenkinsop, Tom (December 2006). "Scarp retreat versus pinned drainage divide in the formation of the Drakensberg escarpment, southern Africa". South African Journal of Geology. 109 (4): 599–610. doi:10.2113/gssajg.109.4.599. Retrieved 2012-12-02.
Parsons, Anthony J. (2009-01-01). Geomorphology of Desert Environments. Springer. ISBN978-1-4020-5719-9. Retrieved 2012-12-02.
Schmidt, Karl-Heinz (1988). "Rates of scarp retreat: A means of dating Neotectonic activity". The Atlas System of Morocco. Lecture Notes in Earth Sciences. Vol. 15. pp. 445–462. doi:10.1007/bfb0011604. ISBN978-3-540-19086-8.
Schmidt, Karl-Heinz (March 1989). "The significance of scarp retreat for cenozoic landform evolution on the Colorado Plateau, U.S.A.". Earth Surface Processes and Landforms. 14 (2): 93–105. Bibcode:1989ESPL...14...93S. doi:10.1002/esp.3290140202.
November 15, 2023
scarp, retreat, geological, process, through, which, location, escarpment, changes, over, time, typically, cliff, undermined, rocks, fall, form, talus, slope, talus, chemically, mechanically, weathered, then, removed, through, water, wind, erosion, process, un. 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 Bandiagara Escarpment in Mali Contents 1 Scarp profiles 2 Mechanism 3 Rate of retreat 4 Examples 5 See also 6 ReferencesScarp profiles edit nbsp Components of a scarp where the caprock slopes back from the rim as is common nbsp Aerial view of retreating scarp in Namibia A scarp is a line of cliffs that has usually been formed by faulting or erosion If it is protected by a strong caprock or if it contains vertical fractures it may retain its steep profile as it retreats 1 Scarps in dry climates typically have a near vertical upper face that may account for 10 75 of the total height with a talus covered sloping rampart forming the lower section The caprock is undermined as the rampart and face are eroded and eventually a section collapses 1 A strong caprock will typically create a relatively high cliff since more undermining is needed to cause it to fail 2 Other factors determining how easily a cliff will fail are the bedding and jointing direction of dip and thickness of the caprock A thin caprock will result in low cliffs that retreat quickly 3 However a caprock is not essential for scarp retreat to occur as higher humidity and weathering at the foot ensures erosion at the foot drives or keeps up with the erosion of the free face 4 5 Mechanism edit nbsp Illawarra escarpment in AustraliaThe most common way in which a scarp retreats is through rockfall where individual blocks calve from the cliff or large sections of the cliff face collapse at once In some high energy situations much of the rock may be powdered in a rockfall and easily eroded Generally though the fallen debris must be weathered and the rampart eroded before scarp retreat can continue 6 Mechanical and chemical weathering followed by wind erosion may operate in arid regions where cliffs may retreat for long distances 1 In such regions large areas of shale badlands may be left behind as the scarp retreats 3 Erosion may be caused by the sea where the scarp runs along a coast or by streams in humid areas 1 Rate of retreat editThe rate of retreat depends on the types of rock and the factors causing erosion A study published in 2006 determined that the rate of scarp retreat in the Colorado Plateau today varies from 0 5 to 6 7 kilometres 0 31 to 4 16 mi per million years depending on the thickness and resistance to erosion of the caprock 7 Retreat of the Great Escarpment in Australia along the river valleys in the New England region appears to be progressing at about 2 kilometres 1 2 mi per million years 8 A study of cuesta scarp retreat in southern Morocco showed an average rate of 1 3 kilometres 0 81 mi per million years in areas with thin conglomerate caprocks Where there were thicker more resistant limestone caprocks the rate of retreat was slower about 0 5 kilometres 0 31 mi per million years 9 Examples editFurther information Great Escarpment The Colorado Plateau has a cuesta scarp topography consisting of slightly deformed strata of alternating harder and softer rocks The climate has been mostly dry throughout the Cenozoic 7 The conspicuous scarps on the plateau have massive sandstone caps over easily weathered rock such as shale Freeze thaw and groundwater sapping contribute to scarp retreat in this region 10 The Drakensberg mountains in South Africa are capped by a layer of Karoo basalts about 1 000 metres 3 300 ft thick which overlay Clarens formation sandstones They have long been considered a classic example of a landform created by scarp retreat following continental break up with the retreat controlled by an inland drainage divide However they have inland facing scarps as well as seaward facing scarps so factors other than continental break up have contributed to their formation A 2006 paper argued that surface process models may be inadequate in explaining rates of scarp retreat which can also be greatly affected by the types of rock encountered as the scarp retreats and by other factors such as climate tectonic processes and possibly plant cover 11 See also editLester Charles King Hillslope evolution Scarp retreat on planet MarsReferences editCitations a b c d Chorley Schumm amp Sugden 1985 p 273 Chorley Schumm amp Sugden 1985 p 273 274 a b Chorley Schumm amp Sugden 1985 p 274 275 Twidale C R 2007 Backwearing of slopes the development of an idea Revista C amp G 21 1 2 135 146 King Lester 1968 Scarps and Tablelands Zeitschrift fur Geomorphologie 12 114 115 Parsons 2009 p 202 a b Schmidt 1989 Johnson 2009 p 205 Schmidt 1988 Parsons 2009 p 203 Moore amp Blenkinsop 2006 Sources Chorley Richard J Schumm Stanley Alfred Sugden David E 1985 Geomorphology Taylor amp Francis p 273 ISBN 978 0 416 32590 4 Retrieved 2 December 2012 Johnson David 2009 11 04 The Geology of Australia Cambridge University Press p 202 ISBN 978 0 521 76741 5 Retrieved 2012 11 29 Moore Andy Blenkinsop Tom December 2006 Scarp retreat versus pinned drainage divide in the formation of the Drakensberg escarpment southern Africa South African Journal of Geology 109 4 599 610 doi 10 2113 gssajg 109 4 599 Retrieved 2012 12 02 Parsons Anthony J 2009 01 01 Geomorphology of Desert Environments Springer ISBN 978 1 4020 5719 9 Retrieved 2012 12 02 Schmidt Karl Heinz 1988 Rates of scarp retreat A means of dating Neotectonic activity The Atlas System of Morocco Lecture Notes in Earth Sciences Vol 15 pp 445 462 doi 10 1007 bfb0011604 ISBN 978 3 540 19086 8 Schmidt Karl Heinz March 1989 The significance of scarp retreat for cenozoic landform evolution on the Colorado Plateau U S A Earth Surface Processes and Landforms 14 2 93 105 Bibcode 1989ESPL 14 93S doi 10 1002 esp 3290140202 Retrieved from https en wikipedia org w index php title Scarp retreat amp oldid 1146820753, wikipedia, wiki, book, books, library,
