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