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Glaciated Landscapes

Freeze-thaw weathering and glacial erosion processes

  • 2 things to know
  • Component 1 Section A

Overview

How freeze-thaw weathering breaks up rock, glacial abrasion and rock flour.

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Key term

Explain how freeze-thaw weathering breaks up rock.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Explain how freeze-thaw weathering breaks up rock.

    Model answer

    Water enters a joint in the rock and freezes, expanding by about 9% and forcing the crack wider. Repeated cycles across 0 °C eventually shatter the rock into angular blocks.

  2. 2

    What conditions are needed for effective freeze-thaw weathering?

    Model answer

    Temperatures must cross 0 °C frequently and water must be available in the rock. Well jointed rock with many entry points is weathered fastest.

  3. 3

    Where does freeze-thaw weathering matter most in a glacial landscape?

    Model answer

    The process is most effective on exposed rock above the ice, such as arêtes, pyramidal peaks and cirque backwalls. Frost-shattered debris then falls onto the glacier below.

  4. 4

    Define glacial abrasion.

    Model answer

    Abrasion is the wearing away of bedrock by rock debris carried in the base of moving ice. The debris acts like the teeth of a file dragged across the rock.

  5. 5

    What conditions are required for abrasion to work?

    Model answer

    The glacier must be sliding, so warm-based conditions are needed. Debris must be present in the basal ice and harder than the bedrock beneath.

  6. 6

    What is rock flour?

    Model answer

    Rock flour is the very fine silt-sized powder produced by abrasion. Meltwater carrying it takes on a distinctive milky blue-grey colour.

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