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Glaciated Landscapes

Cirques, arêtes and pyramidal peaks

  • 2 things to know
  • Component 1 Section A

Overview

Process of nivation, formation of a cirque from start to finish and typical dimensions of a cirque.

What you need to know

Answer each one before you reveal it.

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Key term

Describe the formation of a cirque from start to finish.

Key term

Define a cirque.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define a cirque.

    Model answer

    A cirque is an armchair-shaped hollow cut into a mountainside by a small glacier. A steep back wall, an over-deepened floor and a raised rock lip are its three parts.

  2. 2

    Explain the process of nivation.

    Model answer

    Snow collects in a shaded hollow and partly melts by day, refreezing at night. Freeze-thaw shatters the rock beneath and meltwater removes the debris, so the hollow deepens.

  3. 3

    Describe the formation of a cirque from start to finish.

    Model answer

    Snow accumulates in a shaded hollow and nivation enlarges it until ice forms. Rotational slip carries the ice round the hollow, so abrasion deepens the floor while meltwater freezing in the bergschrund lets plucking steepen the back wall.

  4. 4

    Why does a cirque have a rock lip at its outer edge?

    Model answer

    Rotational movement lifts the ice slightly as it leaves the hollow. Erosion is therefore weakest at the outer edge, and a bar of less eroded rock is left there.

  5. 5

    What is a tarn?

    Model answer

    A tarn is a small lake occupying the floor of an abandoned cirque. The rock lip dams the meltwater once the ice has gone.

  6. 6

    Give a named UK cirque and its tarn.

    Model answer

    Red Tarn sits in the cirque on the eastern face of Helvellyn in the Lake District. Cwm Idwal in Snowdonia holds Llyn Idwal in the same way.

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