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Describe and explain the variety of landforms found in periglacial areas.

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Introduction

Describe and explain the variety of landforms found in periglacial areas The term periglacial literally means 'around the ice'. Periglacial regions are characterised by persistently low temperatures, but are not covered by glacial ice. The processes associated with periglacial regions, usually take place in areas where the mean annual air temperature is below 3�C. Such areas usually experience short cool summers and long cold winters. At present, areas such as the Tundra of northern Russia, the USA and Canada, together with high mountainous regions such as the Alps, experience a periglacial climate. There are a number of different processes, which produce these periglacial landforms. These processes are frost action including shattering (wedging and splitting), heave and cracking, mass movement including solifluction, nivation and fluvial processes. Frost action is one of the most important processes in periglacial regions, which results in the physical breakdown of rocks into finer particles as water turns to ice and expands. Frost action can also cause the ground surface to expand upwards by up to 5cm per year, a process known as frost heave. In some periglacial areas, frost heave produces irregular, hummocky surfaces covered with small frost mounds. Frost action is responsible for the development of patterned ground, an array of small-scale, geometric features found at the surface of a regolith that has been disturbed by frost action. ...read more.

Middle

Preserved ice wedges are found in Wolverhampton embedded in the boulder clay. If thawing of the surface is continuous, ice wedges may melt and create small depressions. In areas where the wedges are particularly numerous and closely spaced, large-scale collapse of the surface may ensue to create major depressions, called alases. These hollows are likely to become centres of drainage, allowing lakes to form in them, which will prevent the permafrost from re-establishing itself at the surface. In Siberia, co-alescence of many adjacent alases has created linear troughs, known as alas valleys, which reach tens of kilometres in length. A pingo is a small, dome-shaped isolated hill, measuring up to 60m in height and 300m across. In the centre of a pingo is an accumulation of ice, which often melts leaving a meltwater lake. These pingo's are formed in two ways, either closed system/Mackenzie type or open system/east Greenland type. The first type is formed when a shallow lake uses stored heat from the summer sun to insulate the ground below, so there is no permafrost able to form surrounding the lake. Instead of permafrost, saturated unfrozen sands surround the lake. Sediments and plants succession then infill the lake. The winter cold then penetrates and begins to freeze the talik (the unfrozen areas). ...read more.

Conclusion

It is prevalent in permafrost areas because of the seasonal thawing of the ground to produce an active layer. It can cause complete mixture of rocks and soils at a particular site. Clays may form in a series of lobes. Other materials form sheets. Solifluction terraces are step-like features with `risers' up to 15 m high and `treads' up to 500 m long. The solifluction sometimes occurs under a vegetation mat, which is pushed forwards and rolled under. This produces a turf-banked lobe. Stone banked terraces form where the vegetation cover is less continuous and stones are more frequent in the active layer. The terraces tend to be smaller, up to 5 m high and 50 m long. The stones accumulate along the lobate front of the terrace because winter freezing pushes them to the surface and moves them down the slope when the terrace in general, is frozen solid. Although both these features are common in permafrost zones, they form in other areas where winter temperatures are low. They can be found at about 800 m in Scotland in the Cairngorms. Solifluction lobes are tongue-shaped masses of active layer with a gentle terrace and steep frontal scarp (1-6 m) where resistance from adjacent materials causes the mass to bulge, which occurs in fields where lobes overlaps one another to from a staircase slope profile composed of alluvium, angular debris from fines to boulders. ...read more.

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