6.6. GLACIERS

Masses of ice moving as sheets over the land (continental glacier or piedmont glacier if a vast sheet of ice is spread over the plains at the foot of mountains) or as linear flows down the slopes of mountains in broad trough-like valleys (mountain and valley glaciers) are called glaciers.

Glaciers are large, slow-moving masses of ice formed from compacted snow. They can exist in various forms: continental glaciers cover vast areas of land, while mountain glaciers flow down valleys. The primary driver of glacier movement is gravity, which pulls the ice down slopes, allowing it to reshape the landscape beneath it.

Think of glaciers like gigantic rivers of ice. Just as you might see water flowing down a hill, glaciers glide slowly down mountain slopes, carving out valleys and changing the terrain over time.

The movement of glaciers is slow unlike water flow. The movement could be a few centimetres to a few metres a day or even less or more. Glaciers move basically because of the force of gravity.

Unlike rivers that can rush down hillsides quickly, glaciers move at a much slower pace. This movement is mainly due to gravity pulling the heavy ice mass. Over time, this slow movement leads to significant erosion and shaping of the land beneath the glacier.

Imagine pushing a heavy box across a floor. You can only push it slowly, and if it’s heavy it may even scrape the floor beneath it. Similarly, glaciers drag along debris, reshaping the ground as they move.

Fragments get dragged along the floors or sides of the valleys and cause great damage through abrasion and plucking. Glaciers can cause significant damage to even un-weathered rocks and can reduce high mountains into low hills and plains.

As glaciers move, they don't just flow smoothly; they also carry rocks and debris. This movement causes 'abrasion' where the glacier grinds against bedrock, and 'plucking' where chunks of rock are pulled away. Over thousands of years, this process can drastically wear down mountains, turning them into smoother, lower hills.

Think of glaciers as nature’s bulldozer. As they advance, they scrape and pick up rocks, much like a bulldozer pushes earth, reshaping the landscape to form valleys and plains.

Cirques are the most common of landforms in glaciated mountains. The accumulated ice cuts these cirques while moving down the mountain tops. They are deep, long and wide troughs or basins with very steep concave to vertically dropping high walls at its head as well as sides.

Cirques form at the heads of glacial valleys where ice accumulates and slowly carves out a bowl-shaped depression. These depressions are steep and often hold water after the glacier melts, forming small lakes called tarns.

Visualize a big scoop of ice cream being carved out of a mountain. The scoop creates a bowl shape that can hold melted ice cream, resembling how glacial movement leaves cirques with lakes in sunny weather.

Horns form through headward erosion of the cirque walls. If three or more radiating glaciers cut headward until their cirques meet, high, sharp pointed and steep sided peaks called horns form.

When multiple glaciers erode the same area, they can create sharp, steep peaks known as horns. This occurs because each glacier carves away the surrounding rock, meeting at a central peak, resulting in pointed mountain tops.

Imagine a cake being sliced from multiple directions. Each cut carves away a piece, ultimately leading to a taller central peak. That’s how horns are formed by the converging action of multiple glaciers.

Glaciated valleys are trough-like and U-shaped with broad floors and relatively smooth, and steep sides. The valleys may contain littered debris or debris shaped as moraines with swampy appearance.

Glacial valleys differ from river valleys; they are U-shaped due to the expansive force of ice rather than the narrow V-shape typically created by water flow. Moraines, which are ridges of debris pushed by glaciers, often litter these valleys, giving them a distinct look.

Think of a U-shaped valley like a wide bowl. Just as a big spoon scoops out ice cream and forms the bowl shape, glaciers carve out these valleys, leaving rocky debris along the edges.

They are long ridges of deposits of glacial till. Terminal moraines are long ridges of debris deposited at the end (toe) of the glaciers. Lateral moraines form along the sides parallel to the glacial valleys.

Moraines are piles of rocks and soil that have been pushed along by glaciers. Terminal moraines mark the furthest advance of a glacier, while lateral moraines form alongside it. These formations help us understand the historical movement of glaciers.

Consider moraines as the piles of leaves left behind after a child sweeps them into a heap. Just like the leaves, the moraine marks show where the glacier last scooped up and deposited material.

Eskers are sinuous ridges formed by meltwater streams flowing beneath a glacier. Outwash plains are areas at the foot of glacial mountains covered with glacio-fluvial deposits.

As glaciers melt, streams can flow beneath them, depositing sorted sediment that forms eskers. Outwash plains are broader areas where meltwater spreads out, dropping finer materials, resulting in flat, fertile land.

Think of eskers like a hose that leaves behind a trail of sand when water flows through it. Similarly, when glaciers melt, the streams carry sediment and deposit it in long, winding ridges on the landscape.

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