Glacier movement — Eduqas A-Level Geography

Glacier movement is a fundamental process in glaciation, explaining how glaciers erode, transport, and deposit material to shape landscapes. In WJEC A-Level Geography, this topic is studied under 'Glaciated Landscapes' and is essential for understanding landform development, such as U-shaped valleys and moraines. Glaciers move due to gravity, but the mechanisms differ between cold-based (polar) and warm-based (temperate) glaciers, influencing erosion rates and landscape impact.

Understanding glacier movement is crucial for predicting future ice sheet behaviour under climate change, as increased melting can accelerate flow via basal lubrication. This topic also links to concepts like glacial budgets, where accumulation and ablation balance affect movement speed. Mastery of this content allows students to explain how features like crevasses and ogives form, and why some glaciers surge while others stagnate.

In the WJEC exam, questions often require students to compare movement types (e.g., internal deformation vs. basal sliding) and relate them to specific landforms. A strong grasp of glacier dynamics also supports answers on periglacial processes and sea-level rise, making it a core component of the glaciation unit.

• →Internal deformation: Ice crystals slip along planes within the glacier, accounting for most movement in cold-based glaciers. This occurs under pressure, with strain rates increasing with ice thickness.
• →Basal sliding: Meltwater at the glacier's base reduces friction, allowing the glacier to slide over bedrock. This is dominant in warm-based glaciers and requires pressure melting point conditions.
• →Plastic flow vs. brittle fracture: Ice behaves plastically under constant stress (flowing like a viscous fluid) but fractures when stress exceeds a threshold, forming crevasses. This duality explains both slow movement and sudden cracking.
• →Glacial surge: A period of rapid movement (up to 100 times normal) caused by changes in basal conditions, such as water pressure build-up. Surges can last months to years and are often cyclic.
• →Velocity profile: Glacier speed varies from base to surface (faster at surface due to internal deformation) and from margins to centre (faster in centre due to less friction). This creates differential movement and stress.

• Distinction between cold-based and warm-based glaciers
• Geographical locations of cold-based and warm-based glaciers
• Rates of movement for different glacier types
• Mechanisms of glacier ice movement: internal deformation
• Mechanisms of glacier ice movement: basal sliding
• Mechanisms of glacier ice movement: sub-glacial bed deformation
• Mechanisms of glacier ice movement: surge conditions
• Mechanisms of glacier ice movement: compressional flow
• Mechanisms of glacier ice movement: extensional flow

• 💡Use specific terminology like 'basal sliding', 'internal deformation', and 'pressure melting point' to demonstrate depth of knowledge. Avoid vague terms like 'the glacier moves'.
• 💡When comparing movement types, always link to glacier thermal regime (cold-based vs. warm-based) and provide an example, e.g., 'In warm-based glaciers like those in the Alps, basal sliding dominates due to meltwater.'
• 💡For higher marks, explain how movement influences landform development. For instance, 'Basal sliding enhances abrasion and plucking, leading to overdeepening and formation of rock basins.'

• Misconception: Glaciers move like a solid block sliding downhill. Correction: Glaciers deform internally and slide at the base; the surface moves faster than the base, and the centre moves faster than the margins.
• Misconception: All glaciers move at the same speed. Correction: Movement rates vary from <1 m/year (cold-based) to >1 km/year (surge-type), depending on temperature, slope, and basal conditions.
• Misconception: Glacier movement stops in winter. Correction: While surface melt may cease, internal deformation continues year-round; basal sliding may slow if meltwater refreezes, but movement persists.