Cryoplanation
Ingeomorphology,cryoplanationor is a term used to both describe and explain the formation ofplains,terraces andpedimentsinperiglacial environments.[1]Uncertainty surrounds the term,[1]and the effectiveness of the cryoplanation process is held to be limited meaning it can only produce small terraces.[2]Instead, many of so-called cryoplanation terraces are likely an expression of the underlyinglithologyandrock structurerather than being unique products of cold-climate processes.[3][4]
Cryoplanation can be seen as a variant ofpediplanationthat is restricted to cold climates.[2]All the cryoplanation surfaces that exist at present date to theQuaternary.[2]
History of the concept
[edit]The existence of flat bedrock surfaces in the mountains of Siberia was noted in the 1930s.Soviet scientistsS.G. Boch and I.I. Krasnov first proposed a cyclical model for the formation these surfaces in 1943. This model influenced central and western European geomorphologists.[3]Carl Troll,writing in German, called these surfaces “solifluktions-rumpf”, andJean Tricart,writing in French called them “penéplaine périglaciaire”.[5]In 1946Kirk Bryancoined the English term “cryoplanation”.[5][6]From the late 1970s onwards these surfaces are seldom mentioned in Russian scientific literature.[3]
Terraces formed by cryoplanation are calledcryoplanation terraces.Czudek described cryoplanation terraces asgently inclined or nearly horizontal bedrock-cut benches on slopes, spurs and on broad interfluvesthat are formed by theparallel retreat of steeper slope segments under periglacial conditions.[7]Additionally, with the effect of cryoplanation on the landscape, thevegetationon these frost-altered terraces is also reshaped. The vegetation tends to be uniquely uniform both laterally and vertically.[8]The results of this unique freeze-thaw cycle are customarily found inArcticperiglacialregions ofEastern SiberiaandAlaska.They may also be found in areas that currently or have sometime in the past experienced intense seasonal freezing orpermafrost.[7]
In 1950 Peltier proposed the existence of a "periglacialcycle of erosion".This would begin with a non-periglaciated landscape. Once-periglaciated mass wasting ofregolithexposes bedrock in the upper slopes. These outcrops are then subject tofrost weatheringthat makes slopes retreat forming extensiveblockfieldsat the base of the bedrock areas. At a later stagesolifluctionwears down summits and fills in topographic lows.[3]
Assessment
[edit]The concept has been questioned. According to geomorphologists Kevin Hall andMarie-Françoise Andréthe theory has caused confusion because of “the almost complete absence of actual data from active cryoplanation terraces”.[6]It is considered unlikely that cryoplanation can produce any large surfaces. Cryoplanation can be defined as a variant of pediplanation that is restricted to cold climates.[2]Some terraces developed onflood basaltin easternLesotho Highlands,Southern Africa, have been suggested to fit most of the criteria to be cryoplanation terraces except they are more the result ofrock structurethan of planation.[4]
See also
[edit]References
[edit]- ^abThorn, Colin E. (2004). "Cryoplanation". In Goudie, A.S. (ed.).Encyclopedia of Geomorphology.pp. 204–205.
- ^abcdMigoń, Piotr(2004). "Planation surface". In Goudie, A.S. (ed.).Encyclopedia of Geomorphology.pp. 788–792.
- ^abcdFrench, Hugh M. (2007).The Periglacial Environment(3rd ed.). John Wiley & Sons Ltd. pp. 244–246.ISBN978-0-470-86588-0.
- ^abGrab, Stefan; van Zyl, Craig; Mulder, Nicholas (2005). "Controls on basalt terrace formation in the eastern Lesotho highlands".Geomorphology.67(3–4): 473–485.Bibcode:2005Geomo..67..473G.doi:10.1016/j.geomorph.2004.11.010.
- ^abWeischet, Wolfgang (1966). "Solifluxión Periglaciar en el Sur de Chile".Estudios Geográficos: Homenaje a D. Humberto Fuenzalida V.(in Spanish). pp. 211–223.
- ^abHall, Kevin; Marie-Françoise André (2010)."Some further observations regardingcryoplanation terraceson Alexander Island "(PDF).Antarctic Science.22(2): 175–183.Bibcode:2010AntSc..22..175H.doi:10.1017/s0954102009990617.hdl:2263/13884.S2CID53467414.
- ^abCzudek, Tadeáš (1995). "Cryoplanation Terraces: A Brief Review and Some Remarks".Geografiska Annaler: Series A, Physical Geography.77(1/2): 95–105.doi:10.2307/521280.JSTOR521280.
- ^Raup, Hugh M. (1951). "Vegetation and Cryoplanation".Ohio Journal of Science.51(3): 105–116.