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Glaciated Landscapes

Glacier mass balance and the equilibrium line

  • 3 things to know
  • Component 01

Overview

Recall questions on glacier mass balance, accumulation, ablation and sublimation, the accumulation zone and equilibrium line, the seasonal balance of an Alpine glacier, water equivalent and net balance calculations, the accumulation area ratio, and why a snout advances or retreats only after a lag.

What you need to know

Answer each one before you reveal it.

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Key term

Describe the seasonal pattern of mass balance for an Alpine glacier through one year.

Key term

Why is mass balance measured in metres of water equivalent rather than metres of snow?

Key term

Explain why there is a lag between a negative mass balance and a visible retreat of the snout.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define glacier mass balance.

    Model answer

    It is the difference between the mass a glacier gains by accumulation and the mass it loses by ablation over a given period, usually a year.

  2. 2

    What is accumulation?

    Model answer

    It is all the processes that add mass to a glacier, chiefly snowfall, together with avalanching, wind-blown snow and rain freezing onto the surface.

  3. 3

    What is ablation?

    Model answer

    It is all the processes that remove mass from a glacier, chiefly melting, together with sublimation, wind erosion of snow and the calving of icebergs.

  4. 4

    Name the process by which ice turns directly into water vapour.

    Model answer

    Sublimation.

  5. 5

    Where on a glacier is the accumulation zone found?

    Model answer

    In the upper part of the glacier, above the equilibrium line, where annual gains of snow exceed annual losses.

  6. 6

    What is the equilibrium line on a glacier?

    Model answer

    It is the line where accumulation exactly equals ablation over a year, separating the accumulation zone above from the ablation zone below.

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AThe lower quartile is the 2nd value, 11 cm.
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