Patterned ground
Patterned groundis the distinct and often symmetricalnatural patternof geometric shapes formed by the deformation of ground material inperiglacialregions. It is typically found in remote regions of theArctic,Antarctica,and theOutbackinAustralia,but is also found anywhere thatfreezingandthawingofsoilalternate; patterned ground has also been observed in the hyper-aridAtacama Desertand onMars.[2][3]The geometric shapes and patterns associated with patterned ground are often mistaken as artistic human creations. The mechanism of the formation of patterned ground had long puzzled scientists but the introduction of computer-generated geological models in the past 20 years has allowed scientists to relate it tofrost heaving,the expansion that occurs when wet,fine-grained,andporoussoils freeze.
Types[edit]
Patterned ground can be found in a variety of forms. Typically, the type of patterned ground in a given area is related to the prevalence of larger stones in local soils and the frequency of freeze-thaw cycles.[4][5][6][7][8][9]
Polygons[edit]
Polygons can form either inpermafrostareas (asice wedges) or in areas that are affected by seasonalfrost.The rocks that make up these raised stone rings typically decrease in size with depth.[6][11]
In the northern reaches of theCanadianBoreal forests,when bogs reach a eutrophic climax and create asedgemat,tamarack larchandblack spruceare often the early colonists within such a polygonal climax sedge mat.[12]
Circles[edit]
Circles range in size from a few centimeters to several meters in diameter. Circles can consist of both sorted and unsorted material, and generally occur with finesedimentsin the center surrounded by a circle of larger stones. Unsorted circles are similar, but rather than being surrounded by a circle of larger stones, they are bounded by a circular margin ofvegetation.[13][6]
Steps[edit]
Steps can be developed from circles and polygons. This form of patterned ground is generally a terrace-like feature that has a border of either larger stones or vegetation on the downslope side, and can consist of either sorted or unsorted material.[4][6]
Stripes[edit]
Stripesare lines of stones, vegetation, and/or soil that typically form from transitioning steps onslopesat angles between 2° and 7°. Stripes can consist of either sorted or unsorted material. Sorted stripes are lines of larger stones separated by areas of smaller stones, fine sediment, or vegetation. Unsorted stripes typically consist of lines of vegetation or soil that are separated by bare ground.[15][16][6]
It has been conjectured that periglacial stripes on Salisbury Plain in England, that happened by chance to align with the solar sunrise atmid summerand sun set atmid winter,gave rise to awe and veneration by prehistoric people that eventually culminated in the building of theStonehenge.[17]
Formation[edit]
Inperiglacialareas and areas affected by seasonal frost,repeated freezing and thawingofgroundwaterforces larger stones toward the surface, as smaller stones flow and settle underneath larger stones. At the surface, areas that are rich in larger stones contain much less water than highlyporousareas of finer grained sediments. These water-saturated areas of finer sediments have a much greater ability to expand and contract as freezing and thawing occur, leading to lateral forces which ultimately pile larger stones into clusters and stripes. Through time, repeated freeze-thaw cycles smooth out irregularities and odd-shaped piles to form the common polygons, circles, and stripes of patterned ground.[18]
Patterned ground occurs in alpine areas with freeze thaw cycles. For example, onMount Kenyaseasonal frost layer is a few centimetres (inches) below the surface in places.[1]Patterned ground is present at 3,400 metres (11,155 ft) to the west of Mugi Hill.[19]These mounds grow because of the repeated freezing and thawing of the ground drawing in more water. There areblockfieldspresent around 4,000 metres (13,123 ft) where the ground has cracked to form hexagons.Solifluctionoccurs when the night temperatures freeze the soil before it thaws again in the morning. This daily expansion and contraction of the soil prevents the establishment of vegetation.[20]
Frost also sorts the sediments in the ground. Once the mantle has been weathered, finer particles tend to migrate away from the freezing front, and larger particles migrate through the action of gravity. Patterned ground forms mostly within the active layer of permafrost.[18][21]
See also[edit]
References[edit]
- ^abGrab, Stefan W.; Gatebe, Charles K.; Kinyua, Antony M. (2004). "Ground Thermal Profiles from Mount Kenya, East Africa".Geografiska Annaler: Series A, Physical Geography.86(2): 131–141.doi:10.1111/j.0435-3676.2004.00219.x.ISSN0435-3676.JSTOR3566103.S2CID129324724.
- ^Sager, Christof; Airo, Alessandro; Arens, Felix L.; Schulze-Makuch, Dirk (2021-01-15)."New type of sand wedge polygons in the salt cemented soils of the hyper-arid Atacama Desert".Geomorphology.373:107481.Bibcode:2021Geomo.37307481S.doi:10.1016/j.geomorph.2020.107481.ISSN0169-555X.
- ^"Southern Hemisphere Polygonal Patterned Ground".Mars Global Surveyor: Mars Orbiter Camera.Malin Space Science Systems. Archived fromthe originalon 27 October 2016.Retrieved8 November2013.
- ^ab"Patterned Ground".Archived fromthe originalon 29 March 2017.Retrieved21 September2016.
- ^Ballantyne, C.K. (1986). "Non-sorted patterned ground on mountains in the Northern Highlands of Scotland".Biuletyn Peryglacjalny.30:15–34.
- ^abcdeAllaby, Michael (2013).A Dictionary of Geology and Earth Sciences.Oxford University Press. p. 429.ISBN978-0-19-107895-8.
- ^Ólafur, Ingólfsson (2006)."Glacial Geology Photos".RetrievedMarch 4,2007.
- ^Kessler M.A.; Werner B.T. (January 2003). "Self-organization of sorted patterned ground".Science.299(5605): 380–3.Bibcode:2003Sci...299..380K.doi:10.1126/science.1077309.PMID12532013.S2CID27238820.
{{cite journal}}:CS1 maint: multiple names: authors list (link) - ^Marchant, D.R.; Lewis, A.R.; Phillips, W.M.; Moore, E.J.; Souchez, R.A.; Denton, G.H.; Sugden, D.E.; Potter Jr., N.; Landis, G.P. (2002). "Formation of Patterned Ground and Sublimation Till over Miocene Glacier Ice in Beacon Valley, Southern Victoria Land, Antarctica".Geological Society of America Bulletin.114(6): 718–730.Bibcode:2002GSAB..114..718M.doi:10.1130/0016-7606(2002)114<0718:fopgas>2.0.co;2.
- ^Sager, Christof; Airo, Alessandro; Arens, Felix L.; Schulze-Makuch, Dirk (2021-01-15)."New type of sand wedge polygons in the salt cemented soils of the hyper-arid Atacama Desert".Geomorphology.373:107481.Bibcode:2021Geomo.37307481S.doi:10.1016/j.geomorph.2020.107481.ISSN0169-555X.
- ^Trevor-Battye, Aubyn (1921)."A Theory of the Origin of Surface-Polygons in Polar Lands".The Geographical Journal.58(4): 306–309.doi:10.2307/1781041.ISSN0016-7398.
- ^C. Michael Hogan. 2008.Black Spruce: Picea mariana,GlobalTwitcher, ed. N. StrombergArchived2011-10-05 at theWayback Machine
- ^Hallet, Bernard (2013)."Stone circles: form and soil kinematics".Phil. Trans. R. Soc. Lond. A.371(2004): 20120357.Bibcode:2013RSPTA.37120357H.doi:10.1098/rsta.2012.0357.PMID24191111.
- ^Davies, Bethan."stone stripes".AntarcticGlaciers.org.Retrieved2022-03-24.
- ^King, R. B. (1971)."Boulder polygons and stripes in the Cairngorm Mountains, Scotland".Journal of Glaciology.10(60): 375–386.Bibcode:1971JGlac..10..375K.doi:10.1017/s0022143000022073.
- ^Ballantyne, Colin K. (2001). "The sorted stone stripes of Tingo Hill".Scottish Geographical Journal.117(4): 313–324.doi:10.1080/00369220118737131.S2CID128558678.
- ^Yirka, Bob; Phys.org."New dig suggests Stonehenge was built to align with summer and winter solstice".phys.org.Retrieved2022-03-24.
- ^abEasterbrook, Don J. (1999).Surface processes and landforms(2nd ed.). Prentice Hall. pp. 418–422.ISBN978-0-13-860958-0.
- ^Baker, B. H. (1967).Geology of the Mount Kenya area; degree sheet 44 N.W. quarter (with coloured map).Nairobi: Geological Survey of Kenya.
- ^Allan, Iain (1981).The Mountain Club of Kenya Guide to Mount Kenya and Kilimanjaro.Nairobi: Mountain Club of Kenya.ISBN978-9966985606.
- ^Perkins, S. (17 May 2003)."Patterns from Nowhere; Natural Forces Bring Order to Untouched Ground".Science News.163(20): 314–316.doi:10.2307/4014632.JSTOR4014632.
External links[edit]
Media related toPatterned groundat Wikimedia Commons
