Erosion and Deposition: Action of Glaciers

In the previous article, we were discussing the evolution of landforms due to the activities of running water and groundwater. This article deals with the evolution of landforms due to another exogenic geomorphic agent – glaciers.

What is a Glacier?

• ➢ Glaciers are a mass of ice moving under its own weight . They are commonly found in the snow-fields.
• ➢ We know that the landmass on the earth is not entirely the same as we see around. Some areas are covered by thick green forests, some with dry hot deserts, some with permanent ice covers etc. Among these varied landmasses, the permanently icecovered regions on the earth surface are called as snow-fields. The lowest limit of permanent snow or snowfield is called as the snowline.
• ➢ A Glacier forms in areas where the accumulation of snow exceeds its ablation (melting and sublimation) over many years, often centuries.
• ➢ They form features like crevasses, seracs etc. A crevasse is a deep crack, or fracture, found in an ice sheet or glacier, as opposed to a crevice that forms in rock.
• ➢ A serac is a block or column of glacial ice, often formed by intersecting crevasses on a glacier.
• ➢ Ogives are alternating wave crests and valleys (troughs) that appear as dark and light bands of ice on glacier surfaces. They are linked to seasonal motion of glaciers; the width of one dark and one light band generally equals the annual movement of the glacier.
• ➢ Glaciers cover about 10 percent of Earth’s land surface and they are the largest freshwater reservoirs on earth.

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