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Describe and explain how the processes operating in permafrost result in landforms specific to periglacial areas.

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Introduction

Describe and explain how the processes operating in permafrost result in landforms specific to periglacial areas. Periglacial areas are found on the edge of glaciers and are characterised by permafrost, freeze thaw action. Summer temperatures rise above freezing point so ice melts. Three types of periglacial regions can be identified these include the Arctic continental, Alpine and Arctic maritime. Periglacial landforms and processes can be classified into five classes, Ground ice, Frost weathering, snow, meltwater and wind. Ground ice involves three processes including ice crystals and lenses (frost heave), ground contractions and freezing of ground water from these processes sorted stone polygons, ice wedges with unsorted polygons and pingos are formed. Frost heave includes several processes, which cause either fine-grained soils such as silt and clays to form small domes or individual stones within the soil to be moved to the surface. It results from the direct formation of ice - either as crystals or as lenses. The thermal conductivity of stone is greater than that of soil this results in the direct formation of ice, the area under a stone becomes colder then the surrounding area and ice crystals form. ...read more.

Middle

However, frost heaving results in small dome-shaped polygons with larger stones found on the outside of the circles, whereas ice contraction produces larger polygons with the centre of the circles depressed in height and containing the bigger stones. The third process of ground ice is the freezing of ground ice. This forms Pingos. A Pingo is an isolated, conical hill upto 90m high and 800m wide. It can only develop in periglacial area and forms as a result of the movement and freezing of water under pressure. Two types generally identified are open and closed system pingos. Where the water is from a distant elevated source, open system pingos are formed, whereas if the supply of water is local, and the permafrost expands, closed systems are formed. When a Pingo collapses ramparts and ponds are left behind. Frost weathering includes the process frost shattering creating landforms such as blockfields, tors and talus (scree). In Periglacial areas mechanical weathering is far more significant then chemical weathering, with freeze- thaw being the dominant process. On relatively flat upland surfaces the extensive spread of large, angular boulders, formed in situ by frost action, are known as blockfields. ...read more.

Conclusion

Any rivers that are found in periglacial areas are braided, with numerous small channels separated by small linear islands. Braiding occurs because the river is carrying to much sediment. Fed by springmelt, the streams are highly erosive and the river is forced to deposit some of its load. The other landform formed is a Dry Valley. Dry valleys are river valleys without a river. They are most commonly found on chalk and limestone. During the periglacial periods, limestone and chalk become impermeable owing to permafrost, and therefore rivers flowed over their surfaces. High rates of fluvial erosion occurred because of springmelt the highly weathered nature of the surface and high rates of carbonation. At the end of the periglacial period normal permeability returned, waters sank into the permeable rocks and valleys were left dry. The lack of vegetation and a plentiful supply of fine, loose material found in glacial environments enabled strong, cold out-blowing winds to pick up large amounts of debris and to redeposit it as loess in areas far beyond its source. Loess deposits consist mostly of unstratified, structureless silt. All of these periglacial landforms can only form as a result of the Periglacial processes such as Nivation etc that have taken place and therefore they are specific to Periglacial areas. ...read more.

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