Glacial systems: movement, landscapes and evidence
Connect ice movement and sediment to landforms, then evaluate evidence of change.
A-level study: check your qualification and chosen options below.
Mass balance and the movement of a glacier
Accumulation adds snow and ice; ablation removes mass through processes including melting and sublimation. Ice movement transfers mass through the glacier. A retreating snout can coexist with ice still moving downslope.
Deformation and, where basal conditions permit, sliding contribute to movement. Temperature, ice thickness and water pressure affect the processes. Avoid treating every glacier as an identical conveyor: cold and warm basal conditions change how ice interacts with its bed.
Worked example
A fictional glacier gains 1.6 m water equivalent and loses 2.1 m in a year: net balance is −0.5 m water equivalent. This is not a direct prediction of snout retreat in metres. Geometry and the transfer of ice also matter.
Common mistake: A retreating glacier does not mean that its ice has reversed direction.
Time series and missing observations · Landscape cross sections
Erosion, deposition and an inherited landscape
Abrasion depends on debris at the ice–bed interface and effective contact. Quarrying involves detachment of rock blocks, influenced by joints and pressure changes. A U-shaped valley is an outcome interpreted from multiple processes over time, rather than a shape created in one season.
Till is deposited directly by ice and often poorly sorted; meltwater can sort and stratify sediment. A ridge’s position alone may be insufficient to distinguish depositional origins. Look at sediment, form and associations with other landforms.
Worked example
A fictional deposit contains angular clasts from 2 mm to 0.8 m in a fine matrix, without clear layering. That description supports a till interpretation, but a defensible identification also needs location and field context.
Common mistake: A smooth valley profile cannot establish when glaciation occurred.
Glacial change, water supply and changing risk
Melting ice can temporarily augment runoff while reducing the store available for later years. The timing and peak of that contribution depend on basin conditions. A short-term gain in water supply can therefore coexist with declining long-term buffering.
Retreat can expose unstable slopes and contribute to the growth of lakes. Risk assessment must examine potential triggers, exposed settlements and warning or evacuation capacity. A growing lake is evidence to investigate, not proof that an outburst will occur.
Worked example
In a fictional catchment, glacier melt supplies 30 million m³ of a 100 million m³ summer flow. If glacier contribution halves and all other inputs remain unchanged, total summer flow becomes 85 million m³: a 15% reduction, not 50%.
Common mistake: The percentage change in one source is not the same as the percentage change in total supply.
Try a different resource
Landscape cross sections
The profile joins six measured points with straight segments. Horizontal units are kilometres and vertical units are metres. The drawn slope angle is exaggerated by these different scales.
Scroll the diagram sideways to see the full resource.
| Distance (km) | Height (m) |
|---|---|
| 0 | 20 |
| 1 | 320 |
| 2 | 620 |
| 3 | 920 |
| 4 | 620 |
| 5 | 20 |
Resource description
0 km along the transect: 20 m above datum; 1 km along the transect: 320 m above datum; 2 km along the transect: 620 m above datum; 3 km along the transect: 920 m above datum; 4 km along the transect: 620 m above datum; 5 km along the transect: 20 m above datum
Write an explanation
Check your answer
- Distinguish mass balance from terminus position.
- Explain the time-dependent contribution to water supply.
- Use a named taught landscape and dated evidence; these fictional examples cannot replace it.
- Compare exposure and capacity before reaching a qualified judgement.
Practise and review a written answer
Read further
- nsidc.org — source or course reference
- nsidc.org — source or course reference
- webapps.bgs.ac.uk — source or course reference
Course links
AQA A-level Geography · Pearson Edexcel A-level Geography
Next topics
Water cycles: budgets, residence time and feedback · Hazard systems: cascades, probability and resilience
Selected teaching for this option. Detailed named landscapes, field evidence and the full specification still need study with your teacher.