Mass balance: the glacier's bank account

A glacier is an open system. Inputs are snowfall, avalanching and blown snow; outputs are melting, sublimation and calving. The books are balanced by the mass balance (or net balance):

• Accumulation zone — upper glacier: snow adds mass. Snow compacts to firn, then to glacial ice as air is squeezed out.
• Ablation zone — lower glacier: melting, sublimation and calving remove mass.
• Equilibrium line (ELA) — where accumulation exactly equals ablation over the year. Its altitude is the single most sensitive indicator of climate: warming pushes the ELA upslope, shrinking the accumulation zone.
• Positive net balance → glacier thickens and the snout advances. Negative net balance → it thins and the snout retreats.

Reading the balance

Your turn — the net mass balance

A survey team measures one balance year on a small valley glacier (hypothetical data). Total accumulation is 1.8 m water equivalent; total ablation is 2.5 m water equivalent.

Why the ice comes and goes

Today ice covers roughly a tenth of the land surface, overwhelmingly in Antarctica and Greenland, with valley glaciers in high mountain chains. During the Pleistocene, ice sheets repeatedly expanded across northern Europe and North America — which is why Britain has a relict glacial landscape with no glaciers in it.

• Glacials (cold stages) and interglacials (warm stages) alternate. We are currently in an interglacial (the Holocene).
• Milankovitch cycles are the pacing mechanism: eccentricity (shape of Earth's orbit, ~100,000-year cycle), obliquity (axial tilt, ~41,000 years) and precession (the wobble of the axis, ~21,000 years). Together they change the distribution of insolation — especially summer insolation at high northern latitudes.
• Crucially, orbital forcing alone is too weak to produce ice ages. It is amplified by feedbacks: the ice–albedo effect (more ice → more reflection → more cooling) and changes in atmospheric CO₂ recorded in ice cores.
• Shorter-term fluctuations (e.g. the cold interval of the Little Ice Age and the widespread glacier retreat since) sit on top of this orbital rhythm.

Evidence you can cite: ice cores (trapped air bubbles → past CO₂ and, via isotopes, temperature), ocean sediment cores (oxygen-isotope stages), and the landforms themselves — moraines and trimlines mark former ice limits. Reconstructing former extent from landforms is a classic Paper 1 skill.

Orbital forcing

Warm-based, cold-based — and why it decides everything

A glacier's thermal regime is the master control on how much work it does. It is about whether meltwater exists at the base.

• Warm-based (temperate) — basal ice is at pressure-melting point, so meltwater lubricates the bed. Movement is dominated by basal sliding and regelation (pressure melting on the upstream side of an obstacle, refreezing on the lee side). Fast-moving, highly erosive. Typical of the Alps.
• Cold-based (polar) — basal ice is frozen to the bed. No basal sliding: movement is by internal deformation (ice crystals shearing past one another) alone. Slow, and does very little erosion — which is why parts of Antarctica preserve ancient landscapes beneath the ice.
• Extending flow where the gradient steepens: ice accelerates, thins, and pulls apart, opening crevasses — greater erosion of the bed. Compressing flow where the gradient eases: ice slows, thickens, and deposits more.
• Surges — sudden, short-lived accelerations, often linked to a build-up of basal meltwater. They can advance a snout rapidly even in a warming climate, so a surging glacier is not evidence against climate change.

The exam link: whenever you are asked to explain the rate of erosion or the scale of a landform, thermal regime should be in the first sentence. Rock hardness, ice thickness, velocity and debris supply are the other four controls.

Glacial erosion, glacial deposition, or fluvioglacial?

Tap a landform, then tap the process group that formed it. This three-way split is exactly what OS-map and photo questions test.

How ice cuts rock — and what it leaves

Three processes, and you must be able to distinguish them:

• Plucking — meltwater seeps into joints, refreezes onto the bedrock, and as the ice moves it pulls blocks away. Needs a warm base and well-jointed rock. Produces the steep, craggy lee side of a roche moutonnée and the back wall of a corrie.
• Abrasion — debris embedded in the ice acts like sandpaper, scouring the bed and leaving striations and rock flour. Needs debris supply, ice movement and pressure.
• Frost shattering (freeze–thaw) — a subaerial process, not a glacial one: water in joints freezes and expands, prising rock apart above the ice surface. It supplies the angular debris that feeds abrasion and moraines.

Which process, which side?

Till or outwash? Read the sediment

This is the classic fieldwork and photo question, and there is a reliable rule. Ice is a lousy sorting agent; water is an excellent one.

• Glacial deposits (till) — unsorted (boulders and clay together), unstratified (no layers), angular to sub-angular clasts. Landforms: lateral, medial, terminal and recessional moraine; drumlins (streamlined, blunt stoss end upstream, tapered lee end — long axis parallel to ice flow); erratics (rock carried far from its source outcrop — proof of ice direction).
• Fluvioglacial deposits — sorted (grain size graded by the water's competence), stratified (layered), and rounded by attrition in meltwater. Landforms: eskers (sinuous ridges from subglacial tunnels), kames and kame terraces, kettle holes (a buried ice block melts and the sediment above collapses) and the outwash plain (sandur) beyond the snout.

Terminal vs recessional moraine. A terminal moraine marks the maximum extent of the ice. Recessional moraines are a series of ridges upvalley, each marking a still-stand during retreat. Dating them lets you reconstruct the rate of retreat — which is why they matter for climate reconstruction, not just for landform naming.

Name that process

Tap a description on the left, then the term it defines. Precision here is the cheapest mark in the topic.

The cold landscape without the ice

Periglacial environments are cold but not glaciated. The defining condition is permafrost — ground that stays below 0 °C for at least two consecutive years — overlain by an active layer that thaws each summer. Because meltwater cannot drain downwards through frozen ground, the active layer becomes saturated, and that single fact drives most of the landforms.

• Frost heave — repeated freezing lifts larger clasts towards the surface; combined with sorting, this produces patterned ground (stone circles on flats, stone stripes on slopes).
• Solifluction — the saturated active layer creeps slowly downslope over the impermeable frozen layer, producing solifluction lobes and terracettes. It works on remarkably gentle gradients.
• Nivation — a complex of freeze–thaw, meltwater removal and mass movement beneath a snow patch; hollows it enlarges may become incipient corries.
• Ice wedges — thermal contraction cracks fill with water, which freezes and widens the crack each year. Pingos — ice-cored hills raised by groundwater freezing (open-system, fed by artesian flow; or closed-system, from a freezing talik beneath a drained lake).
• Blockfields (felsenmeer) — plateaux of shattered angular rock produced by frost weathering.
• Thermokarst — the hummocky, waterlogged terrain that develops when permafrost thaws. It is the landform of a warming Arctic, and it destabilises roads, pipelines and buildings.

Britain's relict periglacial features (blockfields, solifluction deposits, fossil ice-wedge casts) are evidence that periglacial conditions extended well beyond the ice margin. This is why exam answers must handle relict landscapes as well as active ones.

Why does the slope move?

Your turn — the rate of retreat

Dated recessional moraines let you calculate how fast a snout has withdrawn. Here is a hypothetical dataset from a monitored valley glacier.

Glaciated landscapes as a contested resource

Edexcel treats these landscapes as places where different players place different values on the same square kilometre — and the resulting conflicts are what "evaluate" questions are built on.

• Tourism and recreation — skiing, mountaineering, hiking. Brings income and jobs, but footpath erosion, honeypot congestion, seasonal employment, second-home inflation of house prices and pressure for new lifts and pistes.
• Hydro-electric power — steep gradients, ribbon lakes and reliable meltwater make glaciated valleys ideal. But dams flood valleys, alter flow regimes and trap sediment.
• Quarrying and mineral extraction — hard, resistant rock is valuable; extraction scars the landscape and generates traffic.
• Farming and forestry — often marginal, but culturally central; upland grazing shapes the ecology that conservationists then want to protect.
• Water supply — meltwater feeds rivers used by cities and irrigation far downstream, especially in Asia and the Andes. This makes distant users stakeholders in an alpine glacier.
• Conservation — national parks, designations and rewilding. Fragile because upland soils are thin, growing seasons short, and recovery from damage is slow.

The player framework: local residents, businesses and tourism operators, energy companies, national and local government, NGOs and conservation groups, indigenous communities, and downstream water users. Name them, give each a motive, and show where their aims collide. That is the AO2 skill.

Why "fragile"?

A warming world and a shrinking cryosphere

Glaciers in most mountain regions have been retreating and thinning, and the consequences run far beyond the ice itself:

• Water insecurity. Glaciers act as a natural reservoir, releasing meltwater in the dry season. Retreat brings a temporary increase in flow, then a long-term decline — the "peak water" problem. Downstream irrigation, HEP and cities are exposed.
• Glacial lake outburst floods (GLOFs). Retreat leaves meltwater ponded behind unstable moraine dams. A dam breach, or a rock/ice avalanche into the lake, can send a destructive flood down a populated valley with almost no warning.
• Slope instability. Debuttressing (removal of the supporting ice) and permafrost thaw destabilise rock walls, increasing rockfall and landslide frequency.
• Sea level. Melting land ice (glaciers and ice sheets) adds water to the ocean; thermal expansion of warming seawater adds more. Melting sea ice does not directly raise sea level, because it is already floating — a distinction examiners love.
• Ecosystems and economies. Species ranges shift upslope; ski resorts at lower altitudes lose snow reliability and turn to snow-making, which itself consumes water and energy.

Management runs from mitigation (cutting emissions — the only fix for the root cause) to local adaptation: GLOF early-warning systems and controlled lake lowering, hazard zoning, reservoir construction, and even reflective covers on ski-resort ice. Conservation instruments include national parks, designations, zoning of visitor pressure, honeypot management and sustainable-tourism accreditation.

Be careful with numbers. Rates of ice loss vary enormously between regions and are frequently revised. Write "of the order of" or "widely reported as" rather than inventing a tonnage — a precise mechanism scores; a wrong statistic loses credibility.

Writing the evaluative essay

Edexcel Paper 1 rewards AO1 (knowledge), AO2 (application and analysis — the bulk of the extended-answer marks) and AO3 (working with sources). For this topic:

• Always run process → landform, never landform → adjective. "The corrie is armchair-shaped" is description. "Rotational slip and plucking of the well-jointed backwall over-deepened the hollow, leaving a rock lip" is explanation.
• Name the control, then rank it. Thermal regime, ice thickness, velocity, debris supply, lithology and structure, and time. Say which dominates in this case and why.
• Handle relict landscapes explicitly. Many British landforms were made by ice that is long gone and have since been modified by periglacial and fluvial processes. Saying so is a discriminator.
• Bring in players and values whenever the question is about use, conflict or management — and show that the "best" outcome depends on whose criteria you use.
• Conclude conditionally. Say to what extent, and on what your judgement depends (scale, timescale, whose values).

Try it: "Evaluate the extent to which glaciated landscapes are more threatened by climate change than by human economic activity." Plan: (1) climate change attacks the system itself — mass balance, ELA, GLOFs, permafrost — and is global and irreversible on human timescales; (2) economic activity (tourism, HEP, quarrying) damages surfaces and ecosystems but is local, regulated and often reversible; (3) but they interact — retreating ice opens new land to development, while snow-making intensifies water use. Judgement: climate change is the greater threat to the landscape system, human activity the greater threat to specific sites.

Sharpening the judgement

The big ideas to know

That is Edexcel Topic 2 (Glaciated Landscapes) — process, landform, people, change. Press Finish to see your score.