6.7. EROSIONAL LANDFORMS

Cirques are the most common of landforms in glaciated mountains. The cirques quite often are found at the heads of glacial valleys. 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. A lake of water can be seen quite often within the cirques after the glacier disappears. Such lakes are called cirque or tarn lakes. There can be two or more cirques one leading into another down below in a stepped sequence.

Cirques are unique landforms created by the eroding action of glaciers found at mountainous areas. They typically appear at the beginnings of glacial valleys. As glaciers move down the slopes, they carve out these cirques, resulting in deep basins with steep walls. After the glacier melts, these basins often fill with water, forming lakes known as tarns or cirque lakes. Additionally, it\u2019s common to find multiple cirques in a stepped manner, where one cirque leads into another below it.

Think of cirques like large scoops taken out of a mountain, similar to how a spoon scoops out ice cream from a tub. Once the ice cream (glacier) melts, the scoop (cirque) can hold melted ice cream (water) left behind, creating a small lake.

Horns form through head ward 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. The divides between cirque side walls or head walls get narrow because of progressive erosion and turn into serrated or saw-toothed ridges sometimes referred to as ar\u00eates with very sharp crest and a zig-zag outline. The highest peak in the Alps, Matterhorn and the highest peak in the Himalayas, Everest are in fact horns formed through headward erosion of radiating cirques.

When glaciers erode the cirque walls, they can create pointed peaks known as horns. These occur when multiple glaciers meet at a specific point, eroding the terrain from different angles. The areas between the cirque walls become narrower due to this ongoing erosion, resulting in sharp-edged ridges known as ar\u00eates. Famous mountains, such as the Matterhorn in the Alps and Mount Everest in the Himalayas, are examples of these horns, showcasing the dramatic effects of glacial erosion.

Imagine a cake being cut from multiple sides \u2013 the spots where the knife meets are like the horns of mountains, and the points where the cuts get narrower resemble the serrated ridges. Just as the cake has peaks where each cut comes together, mountains have these peaks shaped by glaciers.

Glaciated valleys are trough-like and Ushaped with broad floors and relatively smooth, and steep sides. The valleys may contain littered debris or debris shaped as moraines with swampy appearance. There may be lakes gouged out of rocky floor or formed by debris within the valleys. There can be hanging valleys at an elevation on one or both sides of the main glacial valley. The faces of divides or spurs of such hanging valleys opening into main glacial valleys are quite often truncated to give them an appearance like triangular facets. Very deep glacial troughs filled with sea water and making up shorelines (in high latitudes) are called fjords/fiords.

Glacial valleys are distinctively shaped by the carving action of glaciers, creating a U-shape rather than a V-shape seen in river valleys. They often feature broad, smooth floors and steep sides. Inside these valleys, you might find debris left behind by the glacier, known as moraines. Sometimes, lakes emerge within these troughs, either from glacial melt or accumulated material. Some glacial valleys may also have higher side valleys known as hanging valleys, which have been cut off and appear as facets along the main valley. In high-latitude regions, deep glacial troughs can become fjords, partially filled with seawater.

Imagine a U-shaped mold that a glacier has pushed through soft dough. Once the glacier melts, the dough leaves behind a wide valley. The hanging valleys can be thought of as shelves sticking out from this U-shaped mold, showcasing how the glacier has shaped the landscape.

What are the basic differences between glacial valleys and river valleys?

Glacial valleys and river valleys differ mainly in their shape and formation process. Glacial valleys tend to be U-shaped due to the broad, heavy ice of glaciers moving through them, while river valleys usually have a V-shape created by flowing water. The steep and smooth sides of glacial valleys result from the powerful scraping effect of glaciers, while river valleys often have more irregular features due to erosion from water flow.

Consider a U-shaped channel carved by a bulldozer versus a wavy creek. The bulldozer represents the glacier, creating broad, smooth walls, while the creek cuts a narrower path through the land, resembling a river valley.

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