The glacier as an open system

A glacier is an open system that exchanges energy and matter (water and ice) with its surroundings.

• Inputs — snowfall, avalanched snow, and rock debris from the valley sides.
• Stores — the ice itself and the sediment it carries.
• Transfers (flows) — the movement of ice downslope, plus meltwater and debris transport.
• Outputs — meltwater, water vapour lost by sublimation, and calving of icebergs where the glacier meets the sea.

Accumulation and ablation: the whole glacier is driven by the balance between mass gained (accumulation) and mass lost (ablation) — the topic we turn to next.

Input or output?

Glacial mass balance & budget

The glacial budget (mass balance) is the difference between accumulation and ablation over a year.

• Zone of accumulation (upper glacier) — accumulation exceeds ablation; net gain.
• Zone of ablation (lower glacier) — ablation exceeds accumulation; net loss.
• Equilibrium line — where accumulation exactly balances ablation over the year.

Your turn — net mass balance

Your turn — retreat rate

How ice moves

• Internal deformation (creep) — ice crystals slowly deform and slide over one another under their own weight; the main movement in cold glaciers.
• Basal sliding — the whole glacier slides over a film of meltwater at its base; important in warm glaciers.
• Regelation — ice melts under pressure on the up-glacier side of an obstacle and refreezes on the down-glacier side, helping the ice flow past it.
• Rotational flow — ice pivots in a hollow (a corrie), deepening it.

Warm (temperate) vs cold (polar) glaciers: warm glaciers sit at pressure-melting point, so meltwater lets them slide fast and erode powerfully; cold glaciers are frozen to their bed, move mainly by internal deformation, and erode little.

Why do warm glaciers move faster?

Glacial weathering & erosion

Weathering in glacial and periglacial environments:

• Freeze-thaw (frost shattering) — repeated freezing and thawing of water in joints shatters rock into angular scree.
• Nivation — a mix of freeze-thaw, chemical weathering and meltwater action beneath a snow patch, hollowing out the ground.

Erosion processes:

• Plucking — meltwater freezes onto rock, and as the glacier moves it pulls away loosened blocks.
• Abrasion — angular debris embedded in the ice base scours the bedrock, leaving striations (scratches) that record the direction of ice flow.

Plucking or abrasion?

Erosional landforms

• Corrie (cirque) — an armchair-shaped hollow with a steep back wall and rock lip, deepened by rotational flow; may hold a tarn.
• Arete — a knife-edge ridge between two corries; a pyramidal peak forms where three or more corries erode back to back.
• Glacial trough (U-shaped valley) — a former V-shaped river valley widened and deepened into a steep-sided, flat-floored trough; spurs are cut back to truncated spurs.
• Hanging valley — a tributary trough left high above the main trough, often with a waterfall.
• Roche moutonnee — a rock knob smoothed by abrasion on the up-glacier (stoss) side and jagged from plucking on the down-glacier (lee) side.
• Ribbon lake — a long, narrow lake in an over-deepened section of a trough.

Name that landform

Transport & depositional landforms

Glaciers carry debris on top, within and beneath the ice, then dump it directly as unsorted, angular till (boulder clay).

• Moraines — ridges of till. Lateral (valley sides), medial (where two glaciers merge), terminal (at the maximum snout position) and ground moraine (spread across the floor).
• Erratics — boulders carried far from their source and left on different bedrock, evidence of ice-flow direction.
• Drumlins — smooth, egg-shaped hills of till, streamlined by moving ice, with a steep stoss (up-glacier) end and tapering lee end.

Till vs outwash: till dumped by ice is unsorted and angular; sediment reworked by meltwater is sorted and rounded — the difference lets you read a landscape.

Fluvioglacial landforms

Fluvioglacial landforms are built by meltwater, so their sediment is sorted (by size) and rounded.

• Outwash plain (sandur) — a flat spread of sorted sand and gravel beyond the snout, coarsest nearest the ice.
• Eskers — long, winding ridges of sand and gravel deposited by meltwater streams in tunnels under the ice.
• Kames — mounds of sorted sediment dropped where meltwater ponded against or on top of the ice.
• Kettle holes — hollows (often lakes) left where a buried block of ice melted and the overlying sediment collapsed.

How was each landform made?

Tap a landform, then tap the group it belongs to.

Match each landform to its description

Tap a description on the left, then its matching landform on the right.

Periglacial environments

Periglacial environments are cold but largely ice-free, dominated by permafrost — permanently frozen ground. In summer the surface thaws into a mobile active layer.

• Patterned ground — stones sorted into circles and polygons by repeated freezing and heaving (frost heave).
• Ice wedges — cracks that fill with water and freeze, widening year on year into wedges of ice.
• Pingos — dome-shaped hills with a core of ice, pushed up as water freezes beneath the surface.
• Solifluction lobes — tongues of saturated active-layer soil that slowly flow downslope over the frozen layer beneath.

The active layer

Human use & management

Glaciated uplands are valued for scenery, water, farming, forestry and above all tourism — but that use creates pressures:

• Footpath erosion and litter from heavy visitor numbers.
• Honeypot congestion, traffic and second-home pressure on local communities.
• Conflicts between conservation, quarrying, reservoirs and recreation.

Management approaches: National Park designation and conservation, footpath repair and zoning of activities, and sustainable tourism that balances protection of fragile landforms with local livelihoods.

The big ideas to know

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