Notes · GeographyUK · A-Levels

Glacial Systems and Landscapes

A physical-landscape option that studies past and present glaciated environments as systems governed by the balance of accumulation and ablation. It covers ice movement and glacial processes, the erosional and depositional landforms of glaciers, fluvioglacial and periglacial features, and the human pressures on fragile cold environments.

6 sections~21 min reading time3 competenciesLevel Standard 4 · Advanced 2

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Exam profile

AO1 · Understand glacial systems, mass balance, and glacial, fluvioglacial and periglacial processes and landformsAO2 · Apply process understanding to explain landform assemblages and evaluate the management of cold environmentsAO3 · Interpret glaciated-upland maps, photographs, mass-balance graphs and cross-profiles

Operators:explainanalyseassessevaluateto what extentdescribe the distributioninterpret

basic level

At AS-Level the emphasis is on describing glacial processes and the main erosional and depositional landforms.

higher level

The full A-Level requires the mass-balance system, the mechanics of ice movement, landform assemblages, and evaluation of fragile environments.

Depth

Text

Contents · 6 sections

Glacial Systems and Landscapes

Glacial systems and the mass balance#

StandardAQA 7037 3.1.4DfE GCE Geography - glacial systems

The glacial mass balance through a year

Fig. 1Illustrative cumulative balance: winter accumulation is offset by summer ablation, ending slightly negative (net retreat).

A glacier is an open system whose behaviour is controlled by its mass balance (or glacial budget): the balance between the inputs of snow and ice and the outputs of melting and evaporation. The inputs, together called accumulation, are the addition of mass by snowfall, avalanche and refreezing, concentrated in the upper accumulation zone. The outputs, together called ablation, are the loss of mass by melting, sublimation and calving, concentrated in the lower ablation zone. Between the two lies the equilibrium line, where a year's accumulation exactly equals a year's ablation.

The net balance over a year determines whether the glacier advances, retreats or stays still. A positive mass balance - accumulation exceeding ablation, typical of a cold year - makes the glacier grow and its snout advance. A negative mass balance - ablation exceeding accumulation, typical of a warm year - makes it shrink and its snout retreat. When accumulation and ablation are balanced over time, the glacier is in dynamic equilibrium and its snout is stationary, even though ice is constantly moving through it from the accumulation zone to the ablation zone.

There is a seasonal rhythm to the budget, just as there is a seasonal water balance in a drainage basin. In winter, snowfall dominates and the glacier gains mass (a positive winter balance); in summer, melting dominates and it loses mass (a negative summer balance). The net annual balance is the sum of the two, and it is the running total over many years that reveals whether a glacier is healthy or in decline. Most of the world's glaciers currently have a negative net balance and are retreating, a direct indicator of a warming climate.

This system framework links directly to landforms and to climate. The steady transfer of ice from the accumulation zone to the ablation zone is what gives a glacier the energy to erode, transport and deposit, so the budget drives the whole landscape. And because the mass balance responds sensitively to temperature and precipitation, glaciers are among the clearest natural indicators of climate change - a retreating snout, a rising equilibrium line and thinning ice are the visible evidence of a negative budget sustained over decades.

\text{net balance} = \text{accumulation} - \text{ablation}

The glacial budget

A positive net balance grows the glacier and advances the snout; a negative net balance shrinks it and causes retreat.

The glacier as a system

Fig. 2Ice is added in the accumulation zone, transferred through the equilibrium line, and lost in the ablation zone.

Worked example

Reading the mass balance

A glacier gains 2.5 m water equivalent of accumulation over the winter and loses 2.8 m water equivalent to ablation over the summer. Calculate the net annual balance and state what will happen to the snout.

Apply the budget
Net balance = accumulation - ablation = $2.5 - 2.8$ .
Calculate
The result is -0.3 m water equivalent - a negative net balance for the year.
$2.5 - 2.8 = -0.3\ \text{m w.e.}$
Interpret
Ablation exceeded accumulation, so the glacier lost mass overall; sustained, this thins the glacier and causes the snout to retreat.

Result: Net balance is -0.3 m water equivalent (negative), so the glacier loses mass and its snout retreats.

Typical mistakes

Assuming a retreating glacier has stopped moving - the ice keeps flowing forward; it is the snout position that retreats because ablation exceeds accumulation.
Confusing accumulation and ablation, or forgetting that the equilibrium line is where they balance.

Active revision

Explain how a sustained negative mass balance leads to the retreat of a glacier's snout, even though the ice within it continues to move forward.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

Ice movement and glacial processes#

StandardAQA 7037 3.1.4DfE GCE Geography - glacial processes

How a glacier moves and erodes

Fig. 3Basal temperature controls the movement mechanism, which in turn controls the rate of plucking and abrasion.

The temperature of the ice at the base of a glacier fundamentally controls how it moves and erodes, so glaciers are divided into warm-based and cold-based types. A warm-based (temperate) glacier has basal ice at or near its pressure melting point, so a film of meltwater lubricates the bed; it moves relatively quickly and erodes actively. A cold-based (polar) glacier is frozen to its bed, with basal temperatures well below freezing; it moves very slowly, mainly by internal deformation, and does comparatively little erosion. Most of the landforms studied were made by warm-based ice.

Glaciers move by two main mechanisms. Internal deformation (creep) is the slow flow of ice crystals under their own weight and gravity; it operates in all glaciers and dominates in cold-based ones. Basal sliding is the slipping of the whole glacier over a lubricating film of meltwater; it operates only in warm-based glaciers and makes them faster. In a corrie, ice also undergoes rotational movement - it slips in a curved, pivoting motion that deepens the rock basin. Where a valley steepens the ice accelerates and thins (extending flow, with crevasses); where it flattens the ice slows and thickens (compressing flow).

Glacial erosion works by two closely linked processes. Plucking (or quarrying) occurs where meltwater beneath the glacier freezes onto the bedrock; as the glacier moves on, it pulls away blocks of rock that have been loosened, especially rock already weakened by freeze-thaw. Abrasion occurs where the rock debris embedded in the base of the ice is dragged across the bedrock, scratching and smoothing it - fine material polishes the surface, while larger fragments cut grooves called striations that record the direction of ice flow.

Once eroded, material is entrained and transported by the ice - carried on the surface (supraglacial), within the ice (englacial) or dragged along the bed (subglacial) - and finally deposited as the ice melts. Away from the ice front, frost action (freeze-thaw weathering) shatters exposed rock, and nivation - a set of processes acting beneath and around a patch of snow, including freeze-thaw and meltwater removal - hollows out the shallow depressions in which corries can begin to form. Together these processes convert the energy of the moving ice into the sculpting of the landscape.

Worked example

Explaining the direction of ice flow

A rock surface shows parallel scratches and, on one side of a knoll, a smooth face while the other side is jagged and stepped. Explain how these features formed and what they reveal.

The scratches
Striations are cut by debris embedded in the base of the ice dragging across the rock (abrasion); their alignment records the direction the ice flowed.
The two faces
The smooth (stoss) face was abraded by ice riding up over it; the jagged (lee) face was plucked as meltwater froze onto loosened blocks and the moving ice pulled them away.
The conclusion
The feature is a roche moutonnee; the smooth side faces up-ice and the plucked side down-ice, so it, like the striations, indicates the flow direction.

Result: Abrasion cut the striations and smoothed the up-ice face; plucking made the steep down-ice face - together they show the ice flowed from the smooth side towards the jagged side.

Typical mistakes

Saying glaciers move only by sliding - cold-based glaciers move by internal deformation and are frozen to the bed.
Confusing plucking (pulling away loosened blocks) with abrasion (scratching and smoothing by embedded debris).

Active revision

Explain why a warm-based glacier erodes its bed more effectively than a cold-based glacier.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

Glacial erosional landforms#

StandardAQA 7037 3.1.4DfE GCE Geography - glacial erosional landforms

A corrie

Fig. 4Plucking steepens the back wall, rotational abrasion over-deepens the basin, and a rock lip dams a tarn.

The corrie (or cirque) is the landform in which many glaciers begin and one of the most examined. It starts as a snow patch in a sheltered, north- or east-facing hollow, where nivation deepens the hollow. As snow accumulates and compacts into ice, the ice erodes the hollow by plucking at the back wall and abrasion at the base, with rotational movement over-deepening the floor into a rock basin. The result is an armchair-shaped hollow with a steep back wall and a rock lip at its lower edge, which after the ice melts often holds a small lake called a tarn.

Where corries erode back to back and side by side, they carve the mountain into sharp features. Two corries eroding towards each other leave a narrow, knife-edged ridge between them called an arete; where three or more corries erode back towards a single point, they leave a sharp pyramidal peak (a horn). These features record the concentration of erosion around the accumulation zones of former glaciers, and reading them lets you reconstruct the pattern of the vanished ice.

Valley glaciers transform the valleys they occupy. A glacier flowing down a former river valley erodes it far more powerfully than the river did, straightening it and deepening and widening it into a steep-sided, flat-floored glacial trough (a U-shaped valley). The ends of the interlocking spurs of the old river valley are sheared off to leave truncated spurs. Smaller tributary glaciers erode less deeply, so after the ice melts their valleys are left high above the main trough as hanging valleys, often with a waterfall spilling from them.

Smaller-scale erosional features complete the assemblage. Roches moutonnees are rock knolls with a smooth, abraded up-ice (stoss) face and a steep, plucked down-ice (lee) face, indicating the direction of flow. Explaining any of these landforms well means combining the process (which mix of plucking and abrasion), the movement (rotational, extending or compressing flow) and the resulting shape, and recognising that they form an assemblage - a whole glaciated upland is legible as the work of former ice.

A glacial trough

Fig. 5A valley glacier deepens and widens a former river valley into a steep-sided, flat-floored U-shaped trough.

Worked example

Reconstructing former ice from landforms

A glaciated upland shows several armchair hollows with tarns, narrow knife-edged ridges between them and a central sharp peak. Explain how this assemblage formed and what it reveals about the former ice.

The hollows
The armchair hollows with tarns are corries, each carved where a small glacier plucked its back wall and abraded and rotated to over-deepen a rock basin.
Ridges and peak
Where two corries eroded back to back they left a knife-edged arete between them; where three or more eroded towards one point they left a pyramidal peak.
The reconstruction
The pattern shows that several small glaciers occupied sheltered hollows around the mountain and eroded backwards, so the ice was concentrated in the accumulation hollows rather than a single ice cap.

Result: Corries, aretes and a pyramidal peak record several small glaciers eroding back from sheltered hollows around the mountain.

Typical mistakes

Describing a corrie's shape without the rotational movement and the plucking/abrasion that over-deepened the basin.
Calling a U-shaped valley a river feature - it is a river valley subsequently deepened and widened by a glacier.

Active revision

Explain how corrie erosion can produce aretes and a pyramidal peak on the same mountain.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

Depositional and fluvioglacial landforms#

StandardAQA 7037 3.1.4DfE GCE Geography - glacial deposition

Classification of glacial deposits

Fig. 6Ice-contact deposits are unsorted and angular; fluvioglacial deposits are sorted and rounded.

Material carried by a glacier is dropped as the ice melts, and the key to classifying the deposits is whether they were laid down directly by ice or by meltwater. Till is the unsorted, angular material deposited directly by the ice: because the ice drops everything together, till is a jumbled mixture of all sizes, from clay to boulders, with the fragments angular because they have not been rounded by water. It is the raw material of the ice-contact depositional landforms.

Moraines are landforms made of till, classified by their position relative to the glacier. Lateral moraines are ridges of debris along the sides of a glacier, weathered from the valley walls; medial moraines run down the centre where two glaciers meet and their lateral moraines merge; a terminal (or end) moraine is a ridge dumped across the valley at the glacier's furthest advance, marking its maximum extent; and ground moraine is the sheet of till spread over the valley floor beneath the ice. Drumlins are smooth, elongated hills of till, shaped by moving ice into a streamlined form with a steep, blunt up-ice (stoss) end and a gentle, tapering down-ice (lee) end, so they too indicate the flow direction. Erratics are boulders carried by the ice and left far from their source rock.

Fluvioglacial landforms are made by meltwater rather than by ice directly, and the crucial difference is that meltwater sorts and rounds the material it carries. Beyond the ice front, braided meltwater streams spread out sorted sand and gravel as an outwash plain (a sandur), with the coarsest material deposited nearest the ice and the finest carried furthest. Eskers are long, winding ridges of sorted sand and gravel deposited in tunnels beneath the ice; kames are mounds of sorted material deposited against or on the ice; and kettle holes are hollows, often now lakes, left where a block of ice buried in the outwash later melted.

The single most useful discriminator in the exam is therefore sorting. If a deposit is unsorted and angular, it was laid down directly by ice (till, moraine); if it is sorted and rounded, and often shows layering (stratification), it was laid down by meltwater (outwash, esker, kame). Being able to justify a landform's origin from the character of its sediment - and to explain the process and the position that produced it - is what distinguishes a strong answer on glacial deposition.

Worked example

Distinguishing till from outwash

Two nearby ridges are examined. Ridge A is a jumbled mixture of angular clay, sand and boulders with no layering. Ridge B is a winding ridge of rounded, sorted sand and gravel showing clear layers. Classify each landform and justify your answer.

Analyse Ridge A
Unsorted, angular material with no layering was dropped directly by melting ice - it is till, so Ridge A is a moraine.
Analyse Ridge B
Sorted, rounded, stratified sand and gravel was deposited by meltwater; a long, winding ridge of such material formed in a tunnel beneath the ice - it is an esker.
State the discriminator
The decisive evidence is sorting and rounding: ice deposits are unsorted and angular; meltwater deposits are sorted, rounded and layered.

Result: Ridge A is a moraine (unsorted, angular till); Ridge B is an esker (sorted, rounded, stratified fluvioglacial material).

Typical mistakes

Calling all glacial deposits 'moraine' - only till landforms deposited by ice are moraines; outwash, eskers and kames are fluvioglacial.
Forgetting that meltwater sorts and rounds sediment, so fluvioglacial deposits are stratified while till is not.

Active revision

Explain how you could determine, from a sediment sample, whether a landform was deposited by ice or by meltwater.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

Periglacial processes and landforms#

AdvancedAQA 7037 3.1.4DfE GCE Geography - periglacial environments

Periglacial processes and landforms

Fig. 7The seasonally thawing active layer over permafrost drives frost action, ground-ice growth and solifluction.

Periglacial environments are the cold, non-glaciated lands on the fringe of ice sheets and in the high latitudes and altitudes, where the ground is frozen but not permanently ice-covered. Their defining feature is permafrost - ground that remains at or below freezing for at least two consecutive years. Above the permafrost lies the active layer, a shallow surface zone that thaws in summer and refreezes in winter; because meltwater cannot drain through the frozen ground below, the active layer becomes saturated and mobile in summer, which drives most periglacial processes.

Frost action is the dominant process. Repeated freezing and thawing shatters exposed rock by freeze-thaw weathering, producing angular debris that mantles slopes as blockfields (felsenmeer). The freezing of water in the ground also sorts and heaves material: frost heave lifts stones towards the surface, and where the ground surface is patterned this produces patterned ground - stone circles and polygons on flat ground and stone stripes on slopes, as the coarse material is pushed aside from the fine.

Ground ice creates its own landforms. Ice wedges form where winter cooling cracks the ground and summer meltwater fills the cracks and refreezes, widening them over many years into wedges of ice; on the surface these produce ice-wedge polygons. Pingos are dome-shaped hills with a core of ice, formed where water freezes and expands beneath the surface and pushes the ground up. Because the active layer becomes waterlogged in summer, saturated soil flows slowly downslope even on gentle gradients, a mass movement called solifluction that produces lobes and terraces of moved material.

Many periglacial landforms in Britain are relict, made during colder phases of the Pleistocene and now preserved in a temperate climate, so recognising them helps reconstruct past conditions. Understanding these processes also matters for the present: as the climate warms, permafrost is thawing, which destabilises the ground, damages buildings and infrastructure built on it, and - as noted in the water and carbon topic - releases stored greenhouse gases, connecting periglacial geomorphology directly to the contemporary climate debate.

Worked example

Explaining solifluction

On a gentle periglacial slope, saturated soil is observed to move slowly downhill in lobes. Explain the process, referring to the active layer and permafrost.

Summer thaw
In summer the active layer thaws while the permafrost beneath stays frozen.
Saturation
Meltwater cannot drain down through the impermeable frozen permafrost, so the active layer becomes saturated and loses cohesion.
Downslope flow
The saturated, weakened soil flows slowly downslope under gravity even on a gentle gradient, piling up into solifluction lobes.

Result: The waterlogged active layer, unable to drain through the permafrost, flows downslope as solifluction, forming lobes.

Typical mistakes

Confusing periglacial (frozen ground, no permanent ice) with glacial (ice-covered) environments.
Forgetting that the active layer becomes saturated because meltwater cannot drain through the frozen permafrost beneath it.

Active revision

Explain why the presence of permafrost is essential to the formation of solifluction lobes.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

Human impact and fragile cold environments#

AdvancedAQA 7037 3.1.4DfE GCE Geography - fragile cold environments

Pressures on fragile cold environments

Fig. 8Multiple pressures act on a slow-recovering environment; management must balance development and conservation.

Cold environments are fragile: their ecosystems and landforms recover very slowly from disturbance because low temperatures mean slow biological growth and slow soil development, and the permafrost is easily destabilised. Yet they are under growing human pressure from resource extraction (oil, gas and minerals, as in Alaska and Siberia), tourism (including in Antarctica and the Alps), hydroelectric power, and settlement and infrastructure. The tension between developing these environments and conserving them is the evaluative heart of this section.

The impacts are distinctive because of the permafrost and the fragility. Building on permafrost is hazardous: the heat from a structure can thaw the ground beneath it, causing it to subside, so buildings and pipelines must be raised on piles or insulated to keep the ground frozen - the trans-Alaska pipeline is the classic example. Vehicle tracks and construction scars in the tundra can persist for decades because vegetation regrows so slowly, and any disturbance of the active layer can trigger erosion and thaw that spreads.

Climate change is now the overarching pressure. Warming is thawing permafrost, retreating glaciers, reducing sea ice and shifting the ranges of cold-adapted species, and these changes both damage existing infrastructure and open the environments to further exploitation - for example, reduced sea ice makes Arctic shipping and drilling more feasible, increasing the pressure precisely as the environment becomes more vulnerable. This creates a difficult feedback between exploitation and change.

Managing these environments requires balancing competing players and interests - resource companies, governments, indigenous peoples, tourists, scientists and conservation groups - across scales from the local to the global. Approaches include international agreements (such as the protection of Antarctica, examined in the human-geography core), protected areas, strict building codes, and sustainable or eco-tourism that limits numbers and impact. The judgement the specification rewards is whether such management can genuinely reconcile development with the conservation of an environment whose fragility means damage is often effectively permanent.

Worked example

Evaluating development on permafrost

A company plans to build a pipeline across permafrost tundra. Evaluate the challenges this poses and how they might be managed.

The permafrost hazard
Heat from the pipeline, and the disturbance of construction, can thaw the permafrost, causing the ground to subside and the pipeline to fracture.
Management options
The pipeline can be raised on insulated piles to keep the ground frozen, routed to avoid the most sensitive ground, and monitored - as with the trans-Alaska pipeline.
Reach a judgement
Engineering can reduce but not eliminate the risk, and construction scars in slow-recovering tundra persist for decades, so a balanced judgement is that development is possible with careful, costly management, but never without lasting impact.

Result: Permafrost thaw is the key hazard; raised, insulated construction manages it, but the slow recovery of the tundra means some impact is unavoidable.

Typical mistakes

Listing human activities without explaining why the impacts are so persistent (slow growth, permafrost sensitivity).
Ignoring the feedback by which climate change both damages the environment and opens it to more exploitation.

Active revision

'The fragility of cold environments makes sustainable development impossible.' To what extent do you agree?

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for geography (Department for Education) · AQA A-level Geography 7037 specification (AQA)

References & sources

Sources

Department for Education

GCE AS and A level subject content for geography

AQA

AQA A-level Geography 7037 specification

Glacial Systems and Landscapes

6 sections~21 min reading time3 competenciesLevel Standard 4 · Advanced 2

Glacial Systems and Landscapes

Key points

Reading the mass balance

Key points

Explaining the direction of ice flow

Key points

Reconstructing former ice from landforms

Key points

Distinguishing till from outwash

Key points

Explaining solifluction

Key points

Evaluating development on permafrost

Sources

Glacial Systems and Landscapes

Key points

Reading the mass balance

Key points

Explaining the direction of ice flow

Key points

Reconstructing former ice from landforms

Key points

Distinguishing till from outwash

Key points

Explaining solifluction

Key points

Evaluating development on permafrost

Sources