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... main types of moraine that can be recognised, lateral moraine, medial moraine, terminal or end moraine, recessional moraines and push moraines. Lateral moraine forms along the edges of the glacier. It is made up of material from the valley walls which is broken up by frost shattering and falls onto the ice surface. It is then carried along the sides of the glacier.
When the ice melts it forms a ridge or embankment of material along the valley side. This can clearly be seen in figure 15. 1, where in the photograph above, the lateral moraine ridge marks the edge of a past glacier of much greater proportions than the one existing today. The present glacier can be seen top left of the image, and is clearly much reduced in size. Figure 15. 1 (web) Medial moraine is found in the centre of a valley. When two glaciers merge, the two edges that meet form the centre line of the new glacier. In consequence two lateral moraines find themselves in the middle of the glacier forming a line of material on the glacier surface.
The existence of a medial moraine is evidence that the glacier has more than one source of arterial. When the ice melts it forms a ridge of material along the valley centre, which is clearly seen in figure 15. 2. The medial moraine is clearly visible as a dark line along the centre of the glacier in figure 15. 2. Figure 15. 2 (web) Recessional moraines form at the end of the glacier so they are found across the valley, not along it.
They mark interruptions in the retreat of the ice when the glacier or ice sheet has remained stationary for sufficient time to produce a mound of material, which can clearly be seen in figure 15. 3. This is a picture of a recessional moraine in the French Alps. The process for the formation of recessional moraines is the same as for a terminal moraine, but they occur where the retreating ice paused rather than at the furthest extent of the ice. Recessional marines are usually parallel to the terminal moraine. Figure 15. 3 (web) Push moraines may develop if the climate becomes poorer after a relatively warm period sufficiently for the ice temporarily to advance again. Then the previously deposited moraine may be shunted up into a mound.
This can be easily recognised by the individual stones which have been pushed upwards form their original horizontal positions. The terminal moraine forms at the snout of the glacier. It marks the furthest extent of the ice, and forms across the valley floor. The terminal moraine resembles a large mound of debris or series of mounds extending across a valley or low land area at right angles to the glacier or ice sheet.
It is usually the feature that marks the end of unsorted deposits and the start of fluvial ly sorted material. Generally terminal and recessional moraines are steeper on their up slope, ice contact side because that is the side into which the glacier has been pushing. One of the best known examples of this in England is the Cromer Ridge in Norfolk. At Cromer the ridge is 90 m high and 8 km long. Congenital moraines can be a great deal larger and a good example of this is the Bloomington Moraine in Illinois, which is more than 300 km long.
There are several other landforms that originate from glacial action. Two landforms called kames and esker's fall into this category. These are the product of glacial rivers, see figure 15. 13. Kames are features that are produced at the margins of the ice and esker's are primarily forms developed beneath the ice. Kames are made up of irregular undulating mounds of bedded sands and gravels that are a group of alluvial cones or deltas deposited unevenly along the front of a stagnant or gradually decaying ice sheet.
Some kames occur as kame terraces because they were formed along the trough between the glacier and the valley side, forming narrow flat popped terrace like ridges. Moulin kames are formed in hollows and perforations in decaying ice, so if they develop along major crevasses they may have an angular dog-leg form. Figure 15. 13 (web) Eskers are elongated ridges of stratified coarse sands and gravels. It is thought that esker's are fossilized courses of subglacial melt water streams. The river channel is restricted by walls of ice, so there is a lot of transported load and hydrostatic pressure in the same area.
Then the bed of the channel builds up because the water has nowhere else to go, therefore material is left above the surrounding land after the retreat of the ice. Eskers in a similar way to kames will form during periods of de glaciation. Kettles and kettle holes are another glacifluvial landform that can be seen in figure 15. 13. These features form from detached blocks of ice left behind as the glacier retreats. These blocks of ice are then partially buried by the glacifluvial deposits left by melt water streams. Then when the ice blocks melt away they leave enclosed depressions in the ground which will then usually fill with water to form kettle-hole lakes.
The topography of the land left behind after the glacier has retreated is often called kame and kettle topography, The glacial system resembles the fluvial system, but the forms adopted by the glacial ice flowing across the land surface and its erosive power, lead to a variety of very distinctive landforms. Larger particle till deposits contain individual stones that are sub-angular, which means that that the particles are not are not rounded like river or beach material and they do not possess sharp edges. The composition of till therefore reflects the character of the rocks over which it has passed in its history. A good example of this is in East Anglia because it is covered by a chalky till due to the glacier passing over a chalk escarpment like the East Anglian Heights. Stones and pebbles that have been carried by the glacier generally become aligned with their long axis parallel to the direction of the ice flow because this offers the least resistance to the ice.
Study of the depositional elements in the till can provide evidence of changes in climate where ice has been exposed for a period of time, or when additional ice formation has occurred. In final conclusion, it is true to say that consideration of glacial till characteristics do reflect the erosion forces which have been applied over time, the effects of transportation in the ice flow and when and where deposition has taken place. References web web web Cook I. Et. Al. , 2000 Geography In Focus, First Edition, Causeway Press, Lancaster. Pickering K.
T. & Owen L. A. 1994, An Introduction To Global Environmental Issues, Routlodge, London. Briggs D. & Smithson P. Et. Al. 1997, Fundamentals Of The Physical Environment, Second Edition, Routlodge, London. Waugh D. 2000, Geography An Integrated Approach, Third Edition, Nelson, Surry.
Strahler A. H. & Strahler A. N. 1976, Environmental Geoscience: Interaction Between Natural Systems And Man, Wiley International Edition, University Press, Oxford.
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