GLACIER

Glaciers are river-like masses of ice which flow down-hill under the action of gravity.
          The distribution of snow is controlled by latitude and altitude. At high latitude and high altitude snow is abundant. The lowest line of perpetual snow is called snow line.
          The place which is covered by snow for ever is called snow field.
A glacier moves, although the rate of movement is so slow that it cannot be perceived by the naked eye. The rate of motion or speed of a glacier depends upon the size of the glacier, the slope of the valley and the average temperature of ice. The depth of the glacier is the greatest in the middle.

2.1 Types of Glacier

a.      Mountain or Valley Glacier
b.     Continental Glacier

a. Mountain or Valley Glacier:

          The mountain glaciers originate above the snow line on the high mountain ranges of the world. In our Himalayas also there are many such mountain glaciers. One of the examples is the Khumbu Glacier of the Sagarmatha zone.

b. Continental Glacier:

          The continental glaciers are the largest among all other types. The biggest continental glacier of Iceland has an area of 8450 sq. km. and has thickness of nearly 1000 meters. The movement of such a glacier is so slow that it may take thousands of years to identify the features developed by it.

2.2 Works of Glacier

          The works of the glacier are the same as that of the river, that is,
a.      Erosion
b.     Transportation
c.      Deposition
When the glacier moves, it carries with it small, thick pebbles, sand stones which are the tools of erosion. These materials are called moraine. So with these tools, the glacier scratches the sharp edges and corners of the rocks and moves them from their original place. The rock pieces lying on the bed are rubbed and they become round. The glacier breaks its lateral rocks with which it deepens its bed. So U-shaped valleys are formed. The larger glaciers have deeper valleys than those of the smaller glaciers. The valleys of the smaller glaciers are found at greater height and those of the larger below them. So the valleys above appear to be hanging and so they are called hanging valleys.
          The glacier carries with it huge quantities of eroded materials which are deposited in the form of moraines. The moraines which are deposited at the end of the glacier are called terminal moraine; those which are left side and right side are known as lateral moraines. Some of the moraines lie beneath the ice are called ground moraines. The moraines of two glaciers deposited at one side are called medial moraines. The moraines lying on the surface are known ablation moraines.

2.3 Importance of Glacier

a.      River origins from the glacier.
b.     Lakes are formed around the glacier influenced area.
c.      Falls are made from the glacier.
d.     Glacier fields are famous for tourism.

2.4 Some terms Related to the Moving Ice

 a. U Shaped Valley

          Normally a glacier flows down the pre-existing river valleys. It is not fluid like rivers and it cannot swing from one side to another following the river valley. Therefore to make its way down the valley, it cuts the river banks and usually flows straight. Thus it modifies the river valley and in the process changes the old V-shaped river valley into U-shaped valley.

b. Moraines

          The fragments of rock materials brought down by the movement of glaciers are known as moraines.