We have already explained, in certain parts of the world, snowfields are formed and glaciers extend from them. These glaciers wear away the valleys in which they are confined, transport rocks, and deposit clay and rocks when they melt. Let’s know how do you know when ice has been at work?
In many ways, the glaciers affect the landscape. In the past, sheets of ice were sculpturing the surface of the Earth in areas which are quite mild in the climate today. Areas such as the English Lake District, Snowdonia of North Wales, and the Alps are all good examples of glaciated landscapes. But what features do all these areas have in common to allow us to tell that they have been affected by ice?
An area that has been glaciated in marked out by two distinctive sets of land features:
- Features resulting from erosion of the area by the glaciers.
- Features which result from depositing of material which had been carved by the ice.
We shall deal with features resulting from erosion first. The ice may carry rock fragments within it and those in contact with any rock surface will surface will scratch it as the glacier passes over the rocks. These grooved rocks are called striated surfaces.
If some of the rocks are harder than others, they may remain raised above the valley floor as ice-moulded hummocks which are smooth on the side facing the direction of the flow of ice and jagged on the other side. These are called roaches mouton nee’s.
Snowfields formed in mountain hollows are cut back and depended on the processes which are associated with the ice and then small glaciers move down a slope. This commonly happens in existing valleys. The armchair-like hollows which are formed at the head of the valley are called cirques, cwms, or corries.
When two or more of these cirques occur on different sides of a mountain, the erosion may cause them to meet, and an arête or a pyramidal peak will remain. The Matterhorn in the Alps is a very famous peak of this kind.
The glacier moving done the valley will cause the valley to become deeper and U-shaped leaving the original tributaries hanging, and any spurs left by the meanderings of the river will be worn away or truncated.
Deposits of rock fragments and clay left behind after glaciations may be doped from the ice itself or from any of the melt waters accompanying it. The haphazard mixture of rock and fine clay is known as drift or till.
It may be dropped at the nose of the glacier as it melts giving rise to the moraine. Sometimes a block of one kind of rock may be carried many kilometers only to fall on a completely different type of rock. This is erratic.
These and many other features give us very strong clause that ice has been at work.
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