Glacial Landforms Created by Erosion

This section explains how glacial landforms were created by erosion. Glaciers are powerful agents of erosion, carving out distinctive landforms as they move. These landforms are created through processes such as plucking, abrasion, and freeze-thaw weathering. As glaciers advance and retreat, they reshape the landscape, leaving behind features such as corries, arêtes, pyramidal peaks, U-shaped valleys, and ribbon lakes.

Corries

A corrie is a deep, armchair-shaped hollow found on the side of a mountain, often the birthplace of a glacier. In France, corries are known as cirques, and in Wales, they are called cwms.

Formation of a Corrie

Snow Accumulation – Snow collects in a sheltered hollow on a mountain’s side, typically on north-facing slopes in the northern hemisphere. The cold, high-altitude conditions prevent the snow from melting in summer.

Compaction into Ice – Over time, more snow accumulates, compressing into ice as air is squeezed out.

Erosion of the Back Wall and Base –

• Freeze-thaw weathering weakens the rock by repeatedly freezing and thawing water in cracks.
• Plucking occurs as the glacier pulls away loosened rocks from the back wall.
• Abrasion deepens the corrie as rock fragments embedded in the glacier grind against the valley floor.

Rotational Slip – As the glacier thickens, it moves downhill in a circular motion known as rotational slip.

Formation of a Corrie Lip – Less erosion occurs at the front of the glacier, leaving behind a raised ridge of material known as a corrie lip.

Creation of a Tarn – When the glacier melts, a lake forms in the hollow, known as a corrie lake or tarn.

Additional Features of Corries

• Arêtes – A narrow ridge formed when two corries erode back towards each other.
• Pyramidal Peaks – When three or more corries erode back into a mountain, a sharp, pointed summit remains, such as the famous Matterhorn in the Alps.

Other Erosional Landforms

As glaciers move downhill, they reshape the landscape by eroding everything in their path.

• U-Shaped Valleys (Glacial Troughs) – Glaciers erode V-shaped river valleys, widening and deepening them into distinctive U-shaped valleys.
• Truncated Spurs – Before glaciation, rivers carve out interlocking spurs. As a glacier advances, it erodes the ends of these spurs, leaving behind steep, truncated spurs.
• Ribbon Lakes – Sometimes, parts of a U-shaped valley are over-deepened due to increased erosion, and when the glacier melts, these areas fill with water, forming ribbon lakes (e.g., Lake Windermere in the Lake District).
• Hanging Valleys – Tributary valleys that once fed into the main valley are left suspended above the main glacial trough after glaciation. When rivers re-establish themselves, waterfalls often form at the edges of hanging valleys (e.g., Yosemite Falls in the USA).

Glacial erosion creates some of the most dramatic landscapes in the world, from the Scottish Highlands to the Alps and beyond. These features not only shape the environment but also provide stunning scenery that attracts millions of visitors each year.