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Explain what is meant by the term 'periglaciation' - Describe and explain the landscape features which result from periglacial processes.

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Introduction

A. Explain what is meant by the term 'periglaciation'. B. Describe and explain the landscape features which result from periglacial processes. The term 'periglacial' is applied to land areas, which lie around the margins of ice sheets and glaciers. These areas can be found in high latitudes and high altitudes. The landforms produced by periglacial processes occur in a range of cold, non-glacial environments, not always adjacent to present-day ice masses. Two main examples would be, the Polar lowlands, e.g. southern Greenland and Highlands, e.g. Rockies, Alps and Himalayas. Frost action and the resulting weathering and mass movement are found not only in periglacial regions. However, within these regions they are especially intense and dominant. The most common environmental characteristic used to delimit present-day periglacial conditions is the presence of permafrost. Permafrost is perennially frozen ground, i.e. ground frozen continuously for two or more years. There are 3 main types of Permafrost: Continuous, is where the ground is completely covered. These areas are usually found in areas such as North Alaska. ...read more.

Middle

The vertical movement is more pronounced, mainly because there is less resistance from the ground surface. The regular repetition of the freeze-thaw, expansion-contraction processes causes churning and movement of materials. This movement causes two of the most distinctive groups of landforms found in periglacial regions, hummocks and patterned ground. A wide variety of hummocky landforms result from the uneven distribution of thrusting and heaving; patterned ground develops because particles of different sizes migrate through the 'active layer' at different speeds. Stone stripes are defined as 'patterned ground with a striped pattern', a sorted appearance due to parallel lines of stones and intervening strips of fine material orientated down the steepest available slope. They can vary greatly in size. An example would be the small-scale stripe formations in the Venezuelan Andes. Different types of hummocks and mounds are 'thufur' and 'palsas'. Thurfur are earth hummocks up to 0.5m high and 1-2m in diameter. They occur in clusters, often with a regular spacing, to give a form of patterned ground, which may cover extensive areas. ...read more.

Conclusion

This can also cause the process of frost heaving which I explained earlier, because over time the growing ice wedge will force the permafrost layer upwards towards the surface and therefore push the soil and rock upwards. This can create the landform 'patterned ground' which I have explained earlier. However, the major feature of frost-crack polygons has occurred in the highland area of Maelifellssandur, southern Iceland. The landforms I have discussed above (e.g. hummocks, patterned ground) develop best on relatively flat terrain. On more strongly sloping surfaces in periglacial regions, a range of mass-movement processes occur, from gradual soil creep through flow surges and slope failures to abrupt rockfalls. A key mechanism is solifluction. First frost heave causes the gradual downslope movement of particles through the operation of the freeze-thaw cycle. Second, gelifluction is the downslope creep caused as the 'active layer' thaws during the summer. Valley shapes are modified by solifluction, to produce valley cambering, stepped cross-profiles and slope-foot and valley-floor deposits. These deposits are widespread throughout the UK. In south-west England, the granite slopes of Dartmoor and Bodmin Moor have well-developed block streams and in southern England block streams are evident in the Marlbourough Downs of Wiltshire and the Portesham area of Dorset. ...read more.

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