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How do glaciers form, move and erode the land, and what landscapes do they leave behind?

The glacial system and mass balance; glacial, fluvioglacial and periglacial processes; erosional and depositional landforms; the periglacial environment; and the human use and management of cold environments.

A focused answer to AQA A-Level Geography 3.1.4, covering the glacial system and mass balance, glacial movement, glacial, fluvioglacial and periglacial processes, erosional and depositional landforms, and the management of cold environments.

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  1. What this dot point is asking
  2. The glacial system and mass balance
  3. Glacial movement and processes
  4. Glacial and fluvioglacial landforms
  5. Periglacial processes and cold-environment management
  6. Try this

What this dot point is asking

AQA section 3.1.4 wants you to understand the glacial system and its mass balance, explain how glaciers move, describe glacial, fluvioglacial and periglacial processes, identify and explain the erosional and depositional landforms they create, and assess the human use and management of cold environments. A key synoptic idea is that the mass balance determines whether a glacier advances or retreats, which in turn controls where erosion and deposition occur.

The glacial system and mass balance

A glacier is an open system with inputs of snow, avalanche and frost, a store of ice, and outputs of meltwater, evaporation, sublimation and calving.

Mass balance varies seasonally (winter accumulation, summer ablation) and over longer cycles. Repeated glacial and interglacial periods of the Pleistocene shaped much of the present landscape, leaving relict features such as drumlin fields well beyond today's ice limits.

Glacial movement and processes

Glaciers move by internal deformation (creep), in which ice crystals slowly slide over one another under their own weight, and, where the base is warm and wet, by basal sliding, lubricated by pressure-melt meltwater. This is why warm (temperate) glaciers, common in mountain regions, move faster and erode more than cold (polar) glaciers frozen to their beds. Crevasse patterns and surges reflect changes in movement.

Erosion is by plucking (meltwater freezes onto rock, then the moving ice pulls fragments away, steepening upglacier faces) and abrasion (rock debris embedded in the ice scours the bed, leaving striations that record ice direction). Freeze-thaw weathering above and beside the ice supplies the angular debris that makes abrasion effective.

Glacial and fluvioglacial landforms

The contrast between till and fluvioglacial deposits is a favourite exam discriminator. Till is dropped directly by ice, so it is unsorted (all sizes mixed) and angular. Fluvioglacial material is carried by meltwater, which sorts it by size and rounds it through attrition, so it is stratified and rounded.

Periglacial processes and cold-environment management

The periglacial environment lies beyond the ice and is dominated by permafrost (ground frozen for at least two consecutive years) with a seasonally thawing active layer on top. Processes include freeze-thaw weathering, frost heave (sorting stones into patterned ground), solifluction (the saturated active layer flowing slowly downslope to form solifluction lobes) and the growth of ground ice, building ice wedges and pingos (ice-cored mounds).

Cold environments are fragile and slow to recover because of low temperatures, short growing seasons and simple food chains. Human pressures include tourism, mineral and energy extraction (Alaskan and Siberian oil and gas), and infrastructure on permafrost, all intensified by climate change that is melting glaciers and thawing permafrost (releasing methane, a positive feedback). Management balances economic use with conservation, careful engineering (elevated, refrigerated pipelines) and the rights of indigenous peoples.

Try this

Q1. Define glacial mass balance. [2 marks]

  • Cue. The difference between accumulation (gains) and ablation (losses) of ice; positive means advance, negative means retreat.

Q2. Distinguish between till and fluvioglacial deposits. [3 marks]

  • Cue. Till is unsorted, angular and ice-deposited; fluvioglacial is sorted, stratified, rounded and meltwater-deposited.

Q3. Explain why warm-based glaciers erode more than cold-based glaciers. [4 marks]

  • Cue. Basal meltwater allows sliding and faster movement, so plucking and abrasion are far more effective than in cold glaciers frozen to their beds.

Exam-style practice questions

Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

AQA 20186 marksExplain the formation of a corrie.
Show worked answer →

A 6 mark "explain" question rewarding a clear process chain (AO1). A corrie (cirque) is a steep, armchair-shaped hollow on a mountainside where a glacier began.

Snow accumulates in a north or east-facing hollow (sheltered from sun and prevailing wind), compacts through firn into glacial ice and moves downslope under gravity by rotational slip. Plucking steepens the back wall as meltwater refreezes onto rock and pulls fragments away; abrasion by debris embedded in the ice deepens and smooths the base, helped by the rotational movement that concentrates erosion in the hollow.

Freeze-thaw weathering above the ice feeds angular debris into the system. When the ice melts, the over-deepened hollow holds a tarn, dammed by a rock lip or moraine. Markers reward linking plucking, abrasion and rotational slip to the armchair shape and the over-deepened basin.

AQA 20219 marksAssess the extent to which cold environments are too fragile to be used for economic development.
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A 9 mark "assess" question (AO1 plus AO2) requiring a judgement. Argue the fragility case: cold ecosystems have low biodiversity, slow growth and short food chains, so recovery from disturbance is very slow; permafrost is destabilised by heated buildings and pipelines (Trans-Alaska pipeline is raised and refrigerated to avoid thaw), and tourism erodes thin tundra soils.

Then weigh development pressures and successes: Alaskan and Siberian oil and gas, Alpine tourism and mineral extraction bring major economic value, and careful technology (elevated infrastructure, seasonal ice roads, environmental impact assessment) can reduce damage. Sustainability and indigenous rights (the rights of Inuit and Sami peoples) frame whether use is acceptable.

Conclude that fragility makes cold environments highly vulnerable but not unusable, provided development is carefully managed and monitored, with climate change the overarching threat that makes both fragility and management harder. Markers reward a calibrated, evidenced judgement.

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