Glaciers are moving masses of ice in polar and high mountain ranges with a permanent ice cover. The height above which there is a permanent cover of snow and ice is called the snowline. In the equatorial regions, the snowline is at a height of 5500 metres above the sea level. As one moves pole wards away from the equator, the height of the snowline decreases gradually. In the polar region, the snowline is at the sea level.
1. Continental Glaciers occur in Polar Regions in the form of extensive and thick ice-sheets covering the entire land surface e.g. Antarctica.
2. Mountain Glaciers occur in high mountain regions as the Alps and the Himalayas. In such area, ice and snow accumulate in depressions and along valley heads near the summits. They move down along the valleys, and are called valley glaciers. Valley glaciers are short in length, not exceeding 100 Km. They descend and melt at lower heights, creating rivers or streams e.g. Ganga and Yamuna originate from such valley glaciers. The snow falling in a mountainous region accumulates in depressions around the summits. As more and more snow accumulates, it gets converted to ice under pressure. The glacial erosion result in arm chair-shaped or circular depressions, called the cirques. They get enlarged due to weathering of rocks along the edges.
As the glacier extends from the cirques along the former river valley, the shape of the valley is changes due to the large glacial volume. The glacier carries large quantities of rock particles, which get embedded at the bottom. The movement of the glacier along the valley modifies the V-shaped valley into a U-shaped valley. A U-shaped valley in a mountain region indicates that it was once covered by valley glaciers. When the glaciers melt in the warmer lower slopes, all the material carried by it is deposited. Such deposits containing irregular heaps of rock material are called moraines.