Davis suggested that a glacial topography is a climatic accident that happens to normal cycle of erosion, i.e., climate gets very cold and the river freezes, instead of rivers of water there are rivers of ice, called glaciers, operating as the main geomorphic agent. The geological action of glaciers, i.e., erosion, transportation and deposition together constitute, what is known as glaciation.
Formation of glaciers:
Under the influence of pressure and moisture, the snow flakes change into a granular ice mass, known as neve in French and ‘firn’ in German. When the ice becomes so thick that the lower layers become plastic, outward or downhill flow commences and an active glacier comes into being.
Type of glaciers:
There are three major types of glaciers:
(i) The valley glaciers (Mountain glaciers or Alpine glaciers).
(ii) Piedmont glacier these are intermediate in form and origin, between valley glacier and ice-sheet. They are formed at the foot of the mountains.
(iii) Ice sheet:
These are huge covers of ice and are also known as ‘Continental glacier’.
Accordingly, there are two types of glacial topography, one related to the valley glaciations and the other to the continental glaciations.
Topography of valley-glaciations:
There are two sets of features resulting from glacial erosion and glacial deposition, (since the rock- wastes and other loads are carried frozen within the ice during their transportation, in case of glaciers).
Erosion by glaciers take place due to (i) plucking, (ii) Rasping and (iii) avalanching.
Plucking is also known as frost-wedging or quarrying. During the summer months the surface parts of a glacier may partially melt. This melt water or rain water seeps down along the sides of the ice mass, finding its way into the cracks and fractures in the rocks along the edges and at the head of the glacier.
At night or when the temperatures drop this water freezes. It breaks up the rock by frost-action, and with the movement of the glacier they are frozen in suspension in the ice.
Rasping is the term used to describe the scraping or abrasion by glacial action. The front edge of glaciers functions as bulldozer, pushing and scraping the ground in front of the ice.
Avalanching is the process of mass-wasting. Along the margins of a valley-glacier the valley sides are scrapped and blocks are broken off which become frozen into the ice and are carried away.
This leads to under-cutting of the sides of the valley and pave the ground for slumping, sliding and debris avalanching which bring great quantities of rock-waste on to the top surface of the glacier.