Question 13 of 20advanced💡 UnderstandLong Answer5 marks

How do glaciers accomplish the work of reducing high mountains into low hills and plains?

Correct Answer

Glaciers are masses of ice that move as linear flows down the slopes of mountains in broad trough-like valleys. Their movement is slow, ranging from a few centimetres to a few metres a day, driven basically by the force of gravity.

As glaciers continue to move, debris gets removed and divides get lowered. The accumulated ice cuts deep, long and wide troughs or basins called cirques at the heads of glacial valleys, with very steep concave to vertically dropping high walls. Glaciated valleys become trough-like and U-shaped with broad floors and steep sides. The faces of divides or spurs are quite often truncated, giving them an appearance like triangular facets.

Through continuous erosion, the slope is reduced to such an extent that glaciers will stop moving. This process eventually leaves only a mass of low hills and vast outwash plains along with other depositional features like moraines. The unassorted coarse and fine debris dropped by melting glaciers is called glacial till, while glacio-fluvial deposits form outwash deposits.

Thus, through the combined processes of erosion and deposition, glaciers accomplish the work of reducing high mountains into low hills and plains.

Exercise: EXERCISES | Q: 3(iii) | (Page 16)
For More Understanding

Explanation

The textbook explains the complete cycle of glacial erosion. Glaciers move due to gravity and cut cirques at mountain tops. As they move down, they erode valleys into U-shaped troughs and truncate divides. Eventually, slopes reduce so much that glaciers stop moving, leaving behind low hills and outwash plains. The answer follows this logical sequence from movement to erosion to final reduction of relief.

Solution Steps

  1. Step 1: Explain glacier movement due to gravity

  2. Step 2: Describe erosional processes - debris removal, divide lowering, cirque formation

  3. Step 3: Explain U-shaped valley formation and truncation of spurs

  4. Step 4: Describe final stage - slope reduction leading to low hills and outwash plains

  5. Step 5: Conclude with depositional features like till and moraines

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