Northern England in the Quaternary period (2.6 Ma to the present) Part 1

	By the end of the Tertiary Britain had moved north to about its present latitude. It was during the Quaternary that a general lowering of world temperature took place which heralded the beginning of a series of very cold to temperate periods collectively known as an Ice Age. During these last 2 million years ice sheets have repeatedly advanced over large areas of North America and Northern Europe on at least four occasions. Various estimates of the thickness of these ice sheets have been made, some being up to one kilometre thick.
Between glaciations the climate improved resulting in interglacial periods. Our present climate is more than likely an interglacial one. Glaciations, especially the last one which ended about 10,000 years ago, had a profound influence on the landscape as we see it today. During the last glaciation, known as the Devensian, Highland areas, such as the Lake District, Scottish Highlands, Southern Uplands and the Cheviot Hills generated ice caps from which ice sheets and glaciers travelled eroding huge amounts of material on their way. Hollows, known as corries in mountain sides and U shaped valleys were produced by the erosive power of ice. This material was redeposited across much of the lowlands as far south as the Midlands. Most of Northern England up to about 1000ft. has a covering of boulder clay.  The effects of the last glaciation are not yet over; Scotland is still rising as it recovers from the weight of ice, while much of England is sinking.
	Glacial erosion. At present about 10% of the earth's surface is covered by ice. Ice forms on land when the temperature is low enough for snow to exist all year round. As the snow layers build up the lower levels solidify into ice. The ice will then begin to move due to gravity and a glacier develops. When glacier ice moves over a land surface it erodes by plucking, gouging and grinding. Plucking occurs when pieces of bedrock frozen in the base of the ice and are plucked out when the glacier moves. Debris collected by plucking provides the tools for grinding and gouging the rocks beneath. Gouging by larger fragments can produce grooves in the underlying bedrock. These grooves are known as glacial striations. Some material may be carried on the surface of a glacier, usually frost shattered debris that has fallen onto the ice from higher ground.
It is the enormous erosive power of glaciers that have produced the characteristic landscape seen in the Lake District, such as the U shaped valleys and the corries and tarns at the heads of the valleys where the ice accumulated. When two glaciated valleys are adjacent to each other, a narrow steep sided ridge is produced known as an arête, a classic example being Striding Edge in the Lake District. Many glacial valleys have been flooded by lakes, e.g. Thirlmere. Meltwater from glaciers and ice sheets can also cut erosive channels. These can be marginal to an ice sheet or a channel created by an overflow from an ice dammed lake. These channels produced by meltwater are known collectively as glacial drainage channels or spillways. Classic examples are Newtondale Gorge which runs north-south from near Goathland to Pickering and that of the Forge valley near Scarborough.

Glacial deposition.  Sediment deposited by glaciers and ice sheets when they melt can vary in size from large boulders to clay sized particles, hence glacial deposits are known as boulder-clay or till. Dumping of material at the end, or snout, of a glacier produces banks of terminal moraine. These are often a ridge or series of ridges which are left during stages of glacier or ice sheet melting. Some moraines may act as dams and cause lakes in some glacial valleys. Ice sheets and glaciers can transport material for large distances. Distinctive rock types can help determine the direction in which the ice has moved. A well known example is the distribution of boulders of Shap Granite which comes from near Shap in the Lake District. Boulders of Shap Granite can be seen across Stainmore and on the North Yorkshire coast, e.g. at Saltburn, Sandsend and Runswick Bay. Such rocks are known as glacial erratics. Sometimes, meltwater flows beneath an ice sheet as sub-glacial streams. These form tunnels and deposit sediment as they flow. When the ice has melted the tunnel sediment can be seen as a winding sandy ridge called an esker. Other glacial features produced by deposition are drumlins which are smooth, streamlined oval-shaped landforms, often blunt at one end and tapered at the other. They may occur singly but are more commonly found in large groups called drumlin fields or drumlin swarms. They are believed to be the result of selective deposition of material which is then streamlined by the advancing ice-sheet. Kames are steep-sided mounds of bedded sand and gravel. They are the result of deposition by meltwater within gaps (crevasses) of stagnant ice. Marginal slumping of kames often occurs when the stagnant ice melts. Kame terraces are continuous valley-side land-forms resulting from deposition of material by meltwater between the margin of the ice-sheet or glacier and the valley side.   Click here for part 2

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