Movement of glaciers

Most of glaciers move at the rate of a few meters per day. They move partly by plastic flow and partly by shear movements.
In the high gradient valleys a mountain glacier flows down the slope much like a water under gravity. But in basin shaped, flat or upland areas where the ice can not move under gravity, the glaciers move as a result of differential pressure within the ice mass.The first type of movement is called gravity flow and the second extrusion flow: a mountain glacier may have gravity flow in one part of its course and extrusion flow another, depending upon the irregularities present in the path.

1. Land forms or features of glacial erosion

i). Hanging valleys

• Since the magnitude of the glacial erosion depends upon the thickness of the ice, main glaciers cut their valleys than those of their tributaries.

• As a result at the junction where a tributary joints the main glacier, the floors of their valleys do not meet at the dam level. The valley of the tributary stand on a higher elevation than that of the main valley. Such valleys are called “hanging valleys”

• When the glacier disappears, the hanging valleys are occupied by stream which discharges into the main valley forming waterfalls.

• When a valley glacier terminated on land, the stream of melt-water flowing on and under the glacier, meets downstream to form a single river.

• The glaciers that end at the sea coast discharge huge cliffs of ice into the sea. Because ice is less dense than water, it floats. Such floating ice is called “iceberg”

ii). Cirques (fig. 1.7)

• The bowl shaped hollows present at the glacier valley heads in the mountains, are called “cirques”.

• They are formed mainly by the quarrying and frost wedging action of ice.

• In cirques, a little gap in generally left between the head of the glaciated alley and the mass of the glacier ice. This gap is known as the “bergscheund”.

2. Land forms due to wind erosion

i). Ventifacts

• Wind armed with sand abrades rock near the ground surface. This effect is called “sand blasting”. When the pebbles and boulders are subjected to sand blasting they develop flat sides and sharp edges.

• If these stones contain coarse crystals of unequal hardness, they become pitted.

• Such stones are pitted, polished and contain sharp edges are called “ventifact”

• These stones are affected by erosion of their windward side.

ii.) Pedestal rock/Mushroom Rocks

• Pedestal rocks are the undercut vertical column of rocks which have wider tops, and narrow bases.

• When the wind blows, the sand particles being travel heavily near the surface and cause undercutting or rock faces. (Fig 1.8)

iii.) Sand Dunes

• The wind generally deposits sand in mounds. These mounds are called sand dunes.

• The sand travelling as bed load in wind accumulates whenever it meets any obstruction, such as a boulder or a bush.

• As the accumulation of sand growth, it traps even more sand.

• In this manner sand dunes are created. (Fig. 1.9)