What is the primary difference between the 'stoss' and 'lee' sides of a Roche Moutonnée?

The stoss side is the upstream side, which is smoothed and polished by abrasion as ice flows over it. The lee side is the downstream side, which is jagged and steep due to the process of plucking.

How does a Roche Moutonnée differ from a Crag and Tail formation?

A Roche Moutonnée is a meso-scale feature formed from a single rock outcrop where the ice flows over it. A Crag and Tail is a macro-scale feature where a large, resistant rock (the crag) protects a 'tail' of softer rock or sediment behind it.

When comparing fluvial and glacial valleys, what is the most significant structural difference?

Fluvial valleys are typically V-shaped due to vertical river erosion and mass movement of the sides. Glacial valleys are U-shaped (troughs) because the ice erodes both the floor and the valley walls simultaneously.

What is a common mistake when identifying the direction of ice flow from striations?

Students often assume striations show the exact start and end points of a glacier. In reality, they only show the orientation of the flow; other features like Roche Moutonnées are needed to confirm which way the ice was actually moving.

Why is it incorrect to classify a drumlin as an erosional landform?

A drumlin is a depositional landform composed of unsorted glacial till (sediment). Erosional landforms, like Roche Moutonnées, are carved directly out of the solid bedrock.

What error occurs if one ignores the role of freeze-thaw weathering in glacial landscapes?

Ignoring freeze-thaw leads to a misunderstanding of how glaciers get their 'tools.' Without the shattering of rock above and beneath the ice, the glacier would lack the sharp debris needed for effective abrasion.

Define the term 'Arête' in the context of glacial geomorphology.

An arête is a narrow, knife-edged ridge of rock. It forms when two neighboring cirques erode toward each other, leaving a thin spine of rock between them.

What is 'Rock Flour' and how is it produced?

Rock flour is a very fine, silt-sized sediment produced by the grinding of rocks at the base of a glacier. It is the primary byproduct of the abrasion process.

A fjord is a glacial trough that has been partially submerged by rising sea levels. They are characterized by steep sides and great depths, often extending far inland.

Why do hanging valleys often feature waterfalls?

Hanging valleys are tributary valleys that were not eroded as deeply as the main valley. When the ice melts, the tributary floor sits high above the main floor, forcing any stream to drop vertically as a waterfall.

Glacial Erosion Landforms & Landscapes | Pearson Edexcel A-Level Geography

Glaciated Landscape & Change

Glacial Erosion Landforms & Landscapes

Summary

Glacial erosion is a powerful geomorphic process that transforms landscapes through the mechanical actions of ice and sub-aerial weathering. By utilizing processes such as abrasion and plucking, glaciers reshape V-shaped fluvial valleys into distinctive U-shaped troughs and create sharp, angular mountain features like cirques and arêtes.

1. Core Erosional Processes

Plucking (Quarrying): This process occurs when meltwater at the base of a glacier freezes into cracks in the bedrock. As the glacier moves, it pulls away large, angular fragments of rock that have become attached to the ice, effectively 'plucking' them from the landscape.
Abrasion: This is the 'sandpaper' effect where rocks and debris embedded in the base of the glacier grind against the underlying bedrock. This process produces rock flour (fine sediment) and results in smoothed surfaces known as glacial polish or long grooves called striations.
Freeze-Thaw Weathering: While technically a sub-aerial process, it is critical to glacial erosion. Water enters rock joints, freezes, and expands by approximately 9%, exerting pressure that shatters the rock and provides the glacier with the sharp tools necessary for further abrasion.

Cross-section of a glacial U-shaped valley showing the main trough, a hanging valley, and striations on the bedrock.

2. Small-Scale Erosional Features

Glacial Striations: These are linear scratches or grooves carved into the bedrock by hard boulders trapped at the base of the moving ice. They are vital for geologists as they indicate the precise direction of historical ice flow.
Glacial Polish: When fine-grained rock flour is dragged across the bedrock under high pressure, it acts as a polishing agent. This results in a smooth, reflective surface on the rock that can persist for thousands of years after the ice has retreated.

3. Macro-Scale Alpine Landforms

Cirques (Corries): These are bowl-shaped depressions found at the head of a glacial valley, formed by rotational ice movement and plucking. Over time, they deepen and may eventually hold a small lake known as a tarn.
Arêtes and Pyramidal Peaks: An arête is a sharp, knife-like ridge formed when two cirques erode back-to-back. If three or more cirques erode into a single mountain summit, they create a pointed, triangular peak known as a horn or pyramidal peak.

4. Valley Landforms & Landscapes

5. Key Distinctions

6. Exam Strategy & Tips