Periglacial Environment Ventifacts Desert Pavement Loess Sand Dunes AEOLIAN LANDSCAPES IN TRANSITION http://www.rockymtnrefl.com/SandDunesVert.html Tayler Hamilton http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/eolian_syst ems/loess.html Periglacial Environment Ventifacts Periglacial processes characterise regions with coldclimates Periglacial used to describe processes and features in areas adjacent to modern ice sheets A periglacial environment is difficult to define What is it? Stones shaped and polished by wind abrasion Aeolian transported sand is dominant factor Created by sand moving in the saltation zone Precise temperature Precise precipitiation cmg.soton.ac.uk Ventifacts http://thedryvalleys.files.wordpress.com/2 009/12/dsc_0907.jpg http://earthsci.org/education/teacher/basicgeol/windes/windes.html Ventifacts Ventifacts can be 3-siders or 4-siders Facets Most common type Produced on surfaces nearly perpendicular to wind direction http://www.goldengatephoto.com/westus/deathval.html Dreikanter http://www.exo.net/~pauld/antarctica/dryvalleys.html Vierkanter Ventifacts Ventifacts Pits Small depression eroded into the surface Best developed on steep surfaces facing prevailing wind Begin and grow from points of weakness What are some possible points of weakness? Grooves U-shaped depressions Grow from pits http://www.tektites.co.uk/desert-weathering.html ron.outcrop.org Ventifacts Ventifacts Flutes Pits Extend across the rock surface linearly on surface facing wind Grooves Aligned parallel to strongest wind direction Dreikanter ipernity.com C http://www.kristallin.de/wek/wek.htm Ventifacts http://bldgblog.blogspot.com/2006_08_01_bldgblog_archive.html Ventifacts Yardang Larger scale ventifact Yardang cont’d... Usually less than 10 m high Can extend for kilometres Stoss side is blunt and steep Common in regions underlain by relatively soft rocks B Most reliable type for determining wind direction http://www.psi.edu/pgwg/images/feb10image.html A Wind eroded ridge that is elongated parallel to prevailing wind (typically 2-3 times longer than they are wide) http://www.gansu.gov.cn/en/Travel_Detail.asp?id=164 Dunhuang Yardang National Geologic Park http://www.gansu.gov.cn/en/Travel_Detail.asp?id=164 Dunhuang Yardang National Geologic Park Ventifacts Desert Pavement How can they be important? Surface is only one or two stone layers thick Former wind conditions are useful for reconstructing periglacial environments Fine sediment under stones Desert Pavement What is it? Provide information about periglacial wind conditions both past and present Removal of finer sediments from the surface This causes deflation Once finer sediment is removed and only rocks are exposed, wind threshold cannot continue to erode Desert Pavement Where is it? Common in alluvial fans and unsorted deposits Occurs under very windy conditions How is it periglacial? Alluvial fans from glacial outwash Katabatic winds next to a glacier http://www.texasbeyondhistory.net/ http://commons.wikimedia.org/wiki/File:Desert_pavement_Myrd alssandur.JPG Desert Pavement How is it important? Rocks in the pavement can be ventifacts Ventifacts help determine wind regime of past Wind regime can help reconstruct past climates Loess What is it? Wind deposited sediment Loess deposits blanket the landscape Silt (>50%) Clay (5-30%) Fine sand (5-10%) http://commons.wikimedia.org/wiki/File:Loess_landscape_china.jpg Loess Loess http://en.wikipedia.org/wiki/File:LoessVicksburg.jpg Where is it from? Cold-climate periglacial sediment deposits Originates from flood plains, i.e. outwash from glacial streams Silt and clay is transported by the wind as dust, it is called loess when it is deposited Thus, loess does not necessarily indicate a periglacial environment due to aeolian transportation Loess structure Particles are angular Porosity is usually <50% Highly cohesive Sudden collapsibility when saturated Forms nearly vertical exposures http://www.teara.govt.nz/en/glaciers-and-glaciation/4/5 Loess http://www.ux1.eiu.edu/~cfjps/1300/glacier_photos.html Loess How is it important? Thick loess sheets of central Europe, Russia and China were deposited in glacial periods http://esp.cr.usgs.gov/info/eolian/task2.html Warmer climatic conditions allow organic layers (Paleosols) to form on the loess deposits Paleosols can be carbon dated Can reconstruct past climatic conditions Thus, loess deposits are archives of past climatic conditions and environmental changes http://www.falw.vu/~prim/pictures.htm Sand Dunes Sand Dunes What is it? Assymetrical mounds of sand that migrate by aeolian erosion Contains: Backslope Crest Slipface What are the requirements for periglacial sand dunes? Sediment supply Wind Lack of vegetation Climate http://earthsci.org/education/teacher/basicgeol/windes/windes.html#Yardangs (i.e. Arid, semi-arid) http://geography.howstuffworks.com/terms-and-associations/sand-dune.htm/printable Sand Dunes Sand Dunes How are they periglacial? Barchan dunes U or V-shaped Unidirectional wind Limited supply of sand Tapering edges point downwind Edges advance relative to the middle segment Periglacial – processes and features in areas adjacent to modern ice sheets or glaciers Sediment supply originates from glacio-fluvial and glacio-lacustrine sediment from glacial outwash and melt water Katabatic winds drive the formation of the dunes http://www.bbc.co.uk/weather/weatherwise/factfiles/basics/wind_localwinds.shtml Sand Dunes http://earthsci.org/education/teacher/basicgeol/windes/windes.html#Yardangs Sand Dunes Transverse dunes Unidirectional wind Abundant supply of sand Linear dunes Narrow ridges that form parallel to prevailing wind directions Wider and steeper at upwind end Tapering downwind Form in areas with limited sand supply Barchan dunes transform into transverse dunes if the sediment supply increases Ridges of sand with steep stoss face http://earthsci.org/education/teacher/basicgeol/windes/windes.html#Yardangs http://earthsci.org/education/teacher/basicgeol/windes/windes.html#Yardangs Sand Dunes How are they important? Dune type Dune size Spacing of dunes Commonalities Ventifacts, loess, desert pavement and sand dunes all rely on: Sediment supply Aeolian activity Vegetation Climate Commonalities Commonalities Each landform type occurs in a transitioning landscape relative to periglacial environments Desert pavement Ventifacts Occur in areas with unsorted deposits Katabatic winds from the adjacent glacier Common in alluvial fans and unsorted deposits Katabatic winds from the adjacent glacier Sand dunes Sediment supply originates from glacial outwash and melt water Katabatic winds from the adjacent glacier Loess Originates from outwash of glacial streams Deposits indicate glacial and interglacial periods My Research MY RESEARCH History GSH were covered by the Laurentide Ice Sheet Ice sheet receded 10 000 – 13 000 ybp, glacio-fluvial and glacio-lacustrine sediment was carried in glacial meltwater As the water drained, sediment became exposed to aeolian processes Bigstick Sand Hills of south-western Saskatchewan Source:Hugenholtz, C.H., Wolfe, S.A., & Moorman, B.J. 2007 How does topography influence the distribution of vegetation? Landscape in Transition Dominant wind direction is from the northwest Dunes are oriented from northwest to southeast Started out as barchan dunes Palliser and Hind expedition (1858 – 1859) “Desolate wastes of blown sand” Landscape in Transition Sand Dunes Climatic warming caused them to change to parabolic dunes between 1810 and 1880 Parabolic dunes U or V-shaped Edges become anchored by vegetation Wind removes sand from central zone and deposits it on leeward slope Middle segment advances relative to outer edges Change is due to transitioning landscape Transformation and stabilisation occurred due to warmer and less arid conditions http://earthsci.org/education/teacher/basicgeol/windes/windes.html#Yardangs Landscapes in Transition Dry sub-humid climate Stabilisation has occurred over the past ~200 years References Less than 1% of dunes are active today Many species have adapted to active sand dune conditions Benn, D.I., & Evans, D.J.A. 1998. Glaciers and Glaciation. London, GB: Arnold Hulett, G.K., Coupland, R.T., & Dix, R.L. (1966). Vegetation of dune sand areas within the grassland region of Saskatchewan. Canadian Journal of Botany, 44: 1307 – 1329 MacLaren, I.S. 1985. Aesthetic mappings of the west by the Palliser and Hind survey expeditions, 1857 – 1859. Studies in Canadian Literature, 10(1) Ritter, D.F, Kochel, R.C., & Miller, J.R. 2002. Process Geomorphology (4th ed.). Long Grove, IL: Waveland Press, Inc. http://www.naturecanada.ca/endangered_ know_our_species_krats.asp Washburn, A.L. 1973. Periglacial processes and environments. London, GB: Fletcher & Son Ltd. Whittow, J. 1984. Dictionary of Physical Geography. London, England: Penguin Books Vegetation grows in specific conditions and it is anticipated patterned growth can be modelled Wolfe, S.A., & Hugenholtz, C.H. 2009. Barchan dunes stabilized under recent climate warming on the northern Great Plains. Geology, 37(11): 1039 – 1042
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