Processes of glacial weathering, erosion and the characteristics and formation of associated landforms and landscapes — WJEC A-Level Geography Revision

    This topic focuses on the geomorphological processes of weathering, erosion, and the resulting landforms in glaciated landscapes. It examines the operation

    Topic Synopsis

    This topic focuses on the geomorphological processes of weathering, erosion, and the resulting landforms in glaciated landscapes. It examines the operation of glaciers as systems, the influence of climate change on glacial budgets, glacier movement, and the formation of macro, meso, and micro-scale erosional and depositional landforms. It also covers periglacial processes and the impact of human activity on these systems.

    Key Concepts & Core Principles

    Exam Tips & Revision Strategies

    Common Misconceptions & Mistakes to Avoid

    Examiner Marking Points

    Processes of glacial weathering, erosion and the characteristics and formation of associated landforms and landscapes

    WJEC
    A-Level

    This topic focuses on the geomorphological processes of weathering, erosion, and the resulting landforms in glaciated landscapes. It examines the operation of glaciers as systems, the influence of climate change on glacial budgets, glacier movement, and the formation of macro, meso, and micro-scale erosional and depositional landforms. It also covers periglacial processes and the impact of human activity on these systems.

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    Objectives
    5
    Exam Tips
    6
    Pitfalls
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    Key Terms
    14
    Mark Points

    Topic Overview

    Glacial weathering and erosion are fundamental processes that shape high-latitude and high-altitude landscapes. Weathering in glacial environments is dominated by freeze-thaw action (frost shattering), where water repeatedly freezes and thaws in cracks, breaking rock into angular fragments. Chemical weathering is limited due to cold temperatures but can occur in subglacial environments where meltwater is present. These weathered materials become tools for glacial erosion.

    Glacial erosion occurs through two main processes: abrasion and plucking. Abrasion happens as debris embedded in the ice scrapes against bedrock, smoothing and polishing it, often leaving striations. Plucking (or quarrying) occurs when meltwater refreezes around jointed bedrock, and as the glacier moves, it pulls out blocks of rock. The effectiveness of erosion depends on ice thickness, velocity, and the hardness of the underlying rock.

    These processes create distinctive landforms. On a small scale, striations and glacial polish indicate abrasion, while crescentic gouges and chatter marks show plucking. Larger landforms include corries (cirques), arêtes, pyramidal peaks, U-shaped valleys, hanging valleys, and ribbon lakes. The formation of each landform involves specific combinations of weathering, erosion, and sometimes deposition. Understanding these processes is crucial for interpreting past glacial environments and predicting landscape change in a warming climate.

    Key Concepts

    Core ideas you must understand for this topic

    • →Freeze-thaw weathering: Water enters cracks, freezes (expands by 9%), and repeatedly thaws, causing rock to fracture into angular scree.
    • →Abrasion: Glacier ice with embedded rock fragments scrapes bedrock, creating striations, polish, and rock flour.
    • →Plucking: Meltwater refreezes around jointed bedrock; glacier movement pulls out blocks, leaving a rough, stepped surface.
    • →Corrie formation: Snow accumulates in a hollow, compacts to ice, and rotational slip deepens the hollow, forming a steep backwall and a rock lip.
    • →U-shaped valley formation: A pre-existing V-shaped river valley is widened and deepened by glacial erosion, creating steep sides and a flat floor.

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Operation of the glacier as a system (inputs, outputs, stores, transfers)
    • Glacial budget and mass balance (positive/negative feedback)
    • Causes of climate change (Quaternary Ice Age, glacials, interglacials, stadials)
    • Glacier movement (cold-based vs warm-based, internal deformation, basal sliding, sub-glacial bed deformation, surge conditions)
    • Types of ice mass (cirque glaciers, valley glaciers, ice sheets, etc.)
    • Processes of glacial weathering (freeze-thaw) and erosion (abrasion, plucking, sub-glacial fluvial erosion)
    • Factors affecting glacial erosion (basal thermal regime, ice velocity, ice thickness, bedrock permeability/jointing)
    • Characteristics and formation of erosional landforms (cirques, pyramidal peaks, arêtes, troughs, ribbon lakes, hanging valleys, truncated spurs, roches moutonnées, crag and tail, striations)

    Marking Points

    Key points examiners look for in your answers

    • Operation of the glacier as a system (inputs, outputs, stores, transfers)
    • Glacial budget and mass balance (positive/negative feedback)
    • Causes of climate change (Quaternary Ice Age, glacials, interglacials, stadials)
    • Glacier movement (cold-based vs warm-based, internal deformation, basal sliding, sub-glacial bed deformation, surge conditions)
    • Types of ice mass (cirque glaciers, valley glaciers, ice sheets, etc.)
    • Processes of glacial weathering (freeze-thaw) and erosion (abrasion, plucking, sub-glacial fluvial erosion)
    • Factors affecting glacial erosion (basal thermal regime, ice velocity, ice thickness, bedrock permeability/jointing)
    • Characteristics and formation of erosional landforms (cirques, pyramidal peaks, arêtes, troughs, ribbon lakes, hanging valleys, truncated spurs, roches moutonnées, crag and tail, striations)
    • Processes of transport and deposition (supraglacial, englacial, subglacial transfers)
    • Characteristics of till (ablation, lodgement, deformation) and moraines (terminal, recessional, lateral, medial, push)
    • Fluvioglacial landforms (eskers, kames, kame terraces, sandurs, varves, kettle holes/lakes)
    • Periglacial processes and features (ice lenses, ice wedge polygons, patterned ground, pingos, thermokarst, nivation hollows, blockfields, scree, solifluction terraces, head deposits, dry valleys, loess plateaux)
    • Variations in processes/landforms over time (seconds to millennia)
    • Human activity impacts (extraction, reservoirs, permafrost degradation, GLOFs)

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Use diagrams to illustrate the formation of landforms (e.g., the cave-arch-stack sequence or cirque formation)
    • 💡Ensure case studies are contemporary (within the last two decades)
    • 💡Explicitly link processes to the resulting landforms in extended responses
    • 💡Use the specialised concepts (causality, equilibrium, feedback, interdependence, risk, systems, thresholds) to structure arguments
    • 💡Practice interpreting OS maps for glacial landforms
    • 💡Use specific terminology: In answers, use terms like 'rotational slip', 'plucking', 'abrasion', 'freeze-thaw', and 'striations' to show depth of knowledge. Avoid vague phrases like 'the ice scraped the rock'.
    • 💡Link processes to landforms: For each landform, explain the sequence of processes. For example, for a corrie: snow accumulation → compaction to ice → rotational slip → freeze-thaw on backwall → plucking at base → formation of rock lip.
    • 💡Include diagrams: In exam answers, a well-labelled diagram of a corrie or U-shaped valley can earn additional marks. Show key features like the backwall, rock lip, and direction of ice movement.

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Confusing erosional processes (e.g., plucking vs abrasion)
    • Failing to link landform formation to specific glacial processes
    • Neglecting the systems framework (inputs/outputs/stores)
    • Confusing periglacial features with glacial features
    • Lack of specific case study examples or contemporary contexts
    • Inaccurate use of terminology regarding glacial budgets and mass balance
    • Misconception: Glaciers erode mainly by scraping like sandpaper. Correction: While abrasion is important, plucking is often more effective in jointed bedrock, removing large blocks and creating much of the relief.
    • Misconception: All glacial valleys are U-shaped. Correction: Many valleys show a 'U' shape, but the degree of modification depends on ice volume, duration, and pre-existing topography. Some valleys are more trough-like with steep sides and a flat floor.
    • Misconception: Corries are formed solely by erosion. Correction: Corrie formation involves both erosion (rotational slip) and weathering (freeze-thaw on the backwall), plus deposition of moraine forming the rock lip.

    Frequently Asked Questions

    Common questions students ask about this topic

    Before You Start

    Prior knowledge that will help with this topic

    • •Basic understanding of the hydrological cycle and how snow accumulates to form ice.
    • •Knowledge of rock types and jointing, as these influence the effectiveness of plucking and freeze-thaw.
    • •Familiarity with river valley formation (V-shaped valleys) to contrast with glacial U-shaped valleys.

    Likely Command Words

    How questions on this topic are typically asked

    Explain
    Assess
    Evaluate
    Discuss
    Analyze
    Compare
    Describe

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