Describe the characteristics of periglacial environments and how they affect human activity - Physical Geography Essay Example
A periglacial environment is an area that is on the edge of an ice sheet; it is an area where frost and snow have a major impact upon the environment - Describe the characteristics of periglacial environments and how they affect human activity introduction. The area is characterised by a layer of permafrost; there are three types, continuous, discontinuous and sporadic. Continuous permafrost may be up to 396m deep and is basically an expanse of frozen ground.
This continuous permafrost is typically found from 65ï¿½N to 75ï¿½N, due to the lack of land in the southern hemisphere at these latitudes, permafrost is hardly ever seen. Discontinuous is basically patchy permafrost where the area covered by permafrost is greater than the area of thawed ground. Typically it is only 45m deep, and is found at latitudes 61ï¿½N to 65ï¿½N. Sporadic permafrost is found at latitudes less than 61ï¿½N, and is an area where the thawed ground is more frequent than the permafrost, this layer only reaches 12m in depth.
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The permafrost mainly doesn’t change; it just remains frozen all year around, except for the top 3m in sporadic permafrost, 1-1.5m in discontinuous permafrost and 0.5m in continuous permafrost. This active layer is the place where all periglacial activity occurs.
Periglacial features are located in places of latitude between 61ï¿½N and 75ï¿½N, and places, which had previously been covered in a layer of permafrost such as southern England and the Northern part of Europe. In England there are a large number of examples of periglacial landforms. Of course these landforms are relict, that is that they were formed during the last ice age, the devensian.
Tors are present all over England, they are formed when frost shattering occurs on the joints and bedding planes of hard rocks such as granite, when wide scale denudation occurs the towers of rock are left behind, the eroded material is removed by solifluction, so it isn’t apparent how the rocks got where they are. Ramblers and tourists in general are attracted to strange landforms such as tors, so they become tourist attractions. Examples are found in Dartmoor, Exmoor and the most famous tors in England the stiperstones in Shropshire.
Patterned ground is also popular with tourists as it is a natural formation of regular hexagons, which is out of the ordinary. They are formed when the thawing of permafrost causes frost heave, which causes fine-grained soils such as silts to expand to form small domes, or individual stones to be moved to the surface. The thermal conductivity of the stones is greater than that of the soil. So ice crystals form under the surface, which in turn push rocks upward, the rocks break the surface and due to gravity, roll down the mounds.
As hexagons are the most efficient shape present in nature, due to their tessellation hexagons are formed, created out of many stones. If the ground that the hexagons are formed upon is at an angle greater than 6ï¿½ then elongated hexagons are formed. Patterned ground can be found on Dartmoor, Exmoor, in Norfolk and Cambridgeshire. Farming is poor in areas which have continued formation of stone polygons as every year more will be formed which will damage ploughs and other farm equipment. This also added to the fact that patterned ground will occur in areas, which have permafrost three quarters of the year, and the other quarter the land has a marsh like appearance due to the large quantity of melt water around. So farming in areas that have permafrost is totally impractical, and probably impossible.
Solifluction deposits are common in the U.K especially on Dartmoor and Exmoor, they are the result of thawing on a slope, gravity causes the layers to move downhill. Solifluction leads to the infilling of valleys and rivers by sands to form solifluction sheets, sheets like this can be seen in the cheviot hills in Northumberland If the source of the solifluction was a nivation hollow, a rock stream, which is an in-filled stream which winds across a landscape. Solifluction deposits are also called heads or coombes in chalky areas of England, i.e. the scarp lands such as the Chilterns.
Solifluction helps to flatten out slopes so could be beneficial to farming. Asymmetrical valleys are the result of solifluction if the valley is in an East-West direction then differential sunlight will affect the valley sides with the south facing slope receiving more heat energy so therefore increasing the solifluction on that side of the valley, an example of this is the lymm valley through which the river lymm flows.
Dry valleys are not so common in the U.K, there are a few examples in the South Downs, they occur when porous/pervious rock have been waterlogged and then, when temperatures are changed are frozen. Water can then flow over these rocks cutting valleys. When periglaciation in this area ceases the water that fed this river can flow into the porous/pervious rock so no water runs into the river valley. The Lulworth cove area near Southampton also has a few dry valleys.
Screes are another example of periglacial landforms
Wind blown deposits called loess are commonplace in periglacial environments they occur on gravel river terraces. The Thames valley is a good place to see them, on either side of the Thames estuary. The deposits are also found in Norfolk in the Breckland. The loess deposits are desiccated sand particles, which can either be good farmland, if it is mixed in with clays or silts; this is the case in France and Germany. Or poor farmland if it is just on its own, this is illustrated by the Breckland which is the largest pine forest in the U.K it has not been cut down as the land is so poor agriculturally, deposits of loess in the U.K are known as brick earth. The Yangtze Chiang River in China is called the yellow river due to its sediment, which it carries. This sediment is loess. In this part of China the loess may be up to 300m deep.