AQA A-Level Geography: Glacial Systems and Landscapes Revision Guide

Glacial Systems and Landscapes is one of the optional topics in AQA A-Level Geography Paper 1 (Physical Geography). Students choose either this topic or Coastal Systems and Landscapes -- most schools teach one or the other. The topic examines how glaciers operate as systems, how they shape landscapes through erosion and deposition, and the legacy they leave in both glaciated and periglacial environments.

A systems approach is central to everything in this topic. Glaciers are open systems with inputs (snowfall, avalanches, rockfall), stores (ice, meltwater), transfers (glacial movement, meltwater flow), and outputs (meltwater, evaporation, sediment). If you understand the system, the processes and landforms follow logically. If you try to memorise landforms without understanding the system, you will struggle to apply your knowledge under exam conditions.

This guide works through the topic systematically -- from the glacial system itself, through processes and landforms, to periglacial environments -- and closes with case study advice and exam technique specific to this option.

The Glacial System: Budget, Movement, and Glacier Types

The Glacial Budget

A glacier's behaviour is governed by its mass balance -- the relationship between accumulation (the gain of snow and ice) and ablation (the loss of ice through melting, sublimation, and calving). In the upper part of a glacier -- the zone of accumulation -- snowfall exceeds melting. In the lower part -- the zone of ablation -- melting exceeds snowfall. The boundary between these two zones is the equilibrium line (sometimes called the firn line).

When accumulation exceeds ablation over the course of a year, the glacier has a positive budget and advances. When ablation exceeds accumulation, the budget is negative and the glacier retreats. A glacier in equilibrium -- where accumulation equals ablation over time -- maintains a roughly stable snout position. Understanding the glacial budget is essential because it determines whether a glacier is growing, shrinking, or holding steady, and this in turn controls which processes dominate and what landforms are created.

How Glaciers Move

Glaciers move through several mechanisms, and the type of movement depends on the thermal regime of the glacier:

• Basal sliding -- The glacier slides over the bedrock on a thin layer of meltwater. This is the dominant mechanism in warm-based (temperate) glaciers, where the base of the ice is at or near the pressure melting point. Basal sliding can account for the majority of glacier movement in temperate environments.
• Internal deformation (plastic flow) -- Ice crystals deform and realign under pressure. This occurs throughout the glacier but is most significant where the ice is thickest. Internal deformation is the primary movement mechanism in cold-based (polar) glaciers, where the base is frozen to the bedrock.
• Extending flow -- Where the gradient steepens, the ice accelerates and stretches, creating crevasses. This typically occurs in the zone of accumulation and where the glacier flows over a steepening slope.
• Compressing flow -- Where the gradient decreases, the ice decelerates and is compressed. This occurs in the zone of ablation and where the glacier meets a shallower gradient. Compressing flow is associated with increased erosion.

Warm-Based vs Cold-Based Glaciers

The distinction between warm-based and cold-based glaciers is fundamental to understanding glacial processes:

Warm-based (temperate) glaciers have basal ice at or near the pressure melting point. Meltwater is present at the base, enabling basal sliding and making these glaciers far more erosive. They move relatively quickly -- often several metres per day -- and are found in mid-latitude mountain environments such as the Alps, the Southern Alps of New Zealand, and parts of Scandinavia.

Cold-based (polar) glaciers have basal ice well below the pressure melting point. The ice is frozen to the bedrock, so basal sliding does not occur and erosion rates are very low. Movement is almost entirely through internal deformation and is very slow -- sometimes only a few centimetres per day. Cold-based glaciers are found in high-latitude polar regions such as interior Antarctica and parts of northern Greenland.

Some glaciers -- particularly large ice sheets -- are polythermal, meaning they have characteristics of both. The edges may be warm-based while the interior is cold-based.

Glacial Surges

Glacial surges are episodes of dramatically accelerated glacier flow -- sometimes 10 to 100 times the normal rate. They can be caused by a buildup of meltwater beneath the glacier reducing friction, or by internal instabilities in the ice. Surges are often periodic and can cause sudden advances of the glacier snout, even when the overall climate trend favours retreat. Surging glaciers pose significant hazards, including outburst floods (jokulhlaups) and the disruption of infrastructure in glaciated valleys.

Glacial Processes

Erosion

Glacial erosion is most effective in warm-based glaciers where basal sliding occurs. The key erosion processes are:

• Plucking (quarrying) -- Meltwater at the base of the glacier seeps into cracks in the bedrock and refreezes, bonding the rock to the glacier. As the glacier moves, it pulls away blocks of rock. Plucking is most effective on the lee (downstream) side of bedrock obstacles, where pressure release allows meltwater to refreeze.
• Abrasion -- Rock fragments embedded in the base of the glacier act like sandpaper, grinding and scratching the bedrock beneath. The effectiveness of abrasion depends on the hardness of the rock fragments relative to the bedrock, the thickness of the ice (which determines the pressure), and the rate of glacier movement. Abrasion produces fine rock flour, which gives glacial meltwater its characteristic milky appearance.
• Freeze-thaw weathering -- Water enters cracks in exposed rock above and around the glacier, freezes and expands (by approximately 9%), and progressively widens the crack. Repeated cycles of freezing and thawing shatter the rock. This process is particularly important on the backwall of corries and on valley sides above the glacier surface.

Erosion rates vary significantly. Warm-based glaciers in steep mountain terrain can erode at rates of several millimetres per year. Cold-based glaciers, by contrast, may barely erode at all -- the frozen bed actually protects the underlying rock. This is why ancient landscapes can be preserved beneath polar ice sheets.

Transportation

Glaciers transport vast quantities of material -- from fine clay-sized particles to house-sized boulders -- through three main pathways:

• Supraglacial -- Material carried on the glacier surface, derived from rockfalls and freeze-thaw weathering on the valley sides above.
• Englacial -- Material carried within the body of the ice, incorporated through burial by fresh snowfall or by falling into crevasses.
• Subglacial -- Material carried at the base of the glacier, derived from plucking and abrasion. Subglacial material tends to be more rounded and striated because it has been subjected to grinding against the bedrock.

Deposition

Glacial deposition occurs when the ice melts or when the glacier loses the energy to carry its load. The material deposited directly by glacier ice is called till (or boulder clay). Till is characteristically unsorted -- a chaotic mixture of particle sizes from clay to boulders -- and unstratified. Individual clasts within till are often angular or sub-angular and may show striations.

Fluvioglacial (glaciofluvial) deposits are laid down by meltwater streams flowing from, through, or beneath the glacier. Because water sorts material by size, fluvioglacial deposits are stratified and sorted, with clear layers of sand, gravel, and silt. This sorting is one of the key ways to distinguish between glacial and fluvioglacial deposits in the field and in exam questions.

Landforms of Erosion

Corries (Cirques)

A corrie is an armchair-shaped hollow on a mountainside, typically with a steep backwall, an overdeepened floor, and a raised lip at the front. Corries form where snow accumulates in a pre-existing north- or northeast-facing hollow (in the Northern Hemisphere), compacts into ice, and develops into a small glacier. Freeze-thaw weathering steepens the backwall, while plucking and abrasion at the base -- aided by rotational movement of the ice -- deepen the floor. The lip forms because erosion is less intense near the glacier snout where the ice is thinner. Many corries contain tarns -- small lakes dammed behind the lip after the ice has melted. Llyn Idwal in Snowdonia and Red Tarn on Helvellyn in the Lake District are well-known examples.

Aretes and Pyramidal Peaks

When two corries erode back-to-back on opposite sides of a ridge, the ridge between them is narrowed into a knife-edge feature called an arete. Striding Edge on Helvellyn is a classic example. When three or more corries erode into the same mountain from different sides, the remaining peak is sharpened into a pyramidal peak (or horn). The Matterhorn in the Alps is the most famous example, though Snowdon in Wales also shows this form.

Glacial Troughs (U-Shaped Valleys)

When a glacier occupies a pre-existing river valley, it erodes it into a distinctive U-shaped cross-profile -- a broad, flat floor with steep, near-vertical sides. The glacier straightens the valley by removing interlocking spurs, leaving truncated spurs -- the abruptly cut-off ends of former ridges. The enormous erosive power of valley glaciers creates troughs that are far wider and deeper than the original river valley. The Great Langdale valley in the Lake District and the Lauterbrunnen valley in Switzerland are excellent examples.

Hanging Valleys

Tributary glaciers are smaller and less erosive than the main valley glacier. After the ice retreats, the tributary valleys are left perched high above the main trough floor, often with waterfalls cascading from them. These are hanging valleys. Staubbach Falls in the Lauterbrunnen valley drops from a hanging valley, and there are numerous examples throughout the Lake District and Snowdonia.

Ribbon Lakes

Ribbon lakes are long, narrow lakes occupying the floor of glacial troughs. They form where the glacier encountered a band of softer rock or where compressing flow increased erosion at a particular point. Windermere, Wastwater, and Ullswater in the Lake District are ribbon lakes, as is Lake Zurich in Switzerland.

Roches Moutonnees

These are asymmetric rock outcrops shaped by glacial erosion. The upstream (stoss) side is smooth and gently sloping, polished by abrasion as ice flows over it. The downstream (lee) side is rough, steep, and jagged, shaped by plucking as the ice pulls away rock fragments. Roches moutonnees indicate the direction of former ice flow and are found throughout glaciated landscapes. Striations on the stoss side -- parallel scratches made by debris in the base of the ice -- provide further evidence of ice movement direction.

Landforms of Deposition

Moraines

Moraines are accumulations of till deposited by a glacier. They come in several types:

• Lateral moraines -- Ridges of debris along the edges of a glacier, formed from material that has fallen from the valley sides onto the glacier surface.
• Medial moraines -- Ridges running down the centre of a glacier, formed where two lateral moraines merge at the confluence of two glaciers.
• Terminal moraines -- Ridges of material deposited at the furthest point of glacial advance. They mark the maximum extent of the glacier and form an arc across the valley.
• Recessional moraines -- Smaller ridges deposited during temporary pauses in glacial retreat. A series of recessional moraines indicates episodic retreat rather than continuous withdrawal.
• Ground moraine -- An uneven layer of till deposited beneath the glacier, creating a hummocky, undulating landscape. Ground moraine covers large areas of lowland Britain.

Drumlins

Drumlins are elongated, streamlined hills of glacial till, shaped like an inverted spoon. The blunt, steeper end (stoss) faces the direction from which the ice advanced, while the tapered, gentler end (lee) points in the direction of ice movement. Drumlins typically occur in groups known as swarms, creating a "basket of eggs" topography. The Ribble Valley and the area around the Solway Firth have well-known drumlin swarms. Their exact formation is debated -- they may result from the glacier moulding previously deposited till, or from deposition around a bedrock core -- but they provide clear evidence of ice flow direction.

Erratics

Erratics are boulders or large rocks that have been transported by a glacier and deposited in an area of different geology. They provide evidence of the direction and distance of glacial transport. The Norber Erratics in the Yorkshire Dales -- dark Silurian greywacke boulders sitting on pale Carboniferous limestone -- are a classic example.

Fluvioglacial Landforms

Meltwater streams, both beneath and beyond the glacier, create distinctive landforms:

• Eskers -- Long, sinuous ridges of sorted sand and gravel deposited by subglacial meltwater streams. They can extend for many kilometres and indicate the course of former meltwater channels beneath the ice. Eskers are particularly common in Scandinavia and across the Canadian Shield.
• Kames -- Mounds of sorted sand and gravel deposited by meltwater at the glacier margins or in depressions on the glacier surface. Kame terraces form along the valley sides where meltwater flows between the glacier and the valley wall.
• Outwash plains (sandur) -- Broad, flat areas of sorted fluvioglacial material deposited beyond the glacier snout by braided meltwater streams. The deposits become finer with distance from the glacier -- coarser gravels are deposited first, finer sands and silts further away. Skeidararsandur in Iceland is an extensive outwash plain.

The key distinction examiners look for: glacial deposits (till) are unsorted and unstratified, while fluvioglacial deposits are sorted and stratified. Being able to explain why -- ice drops everything when it melts, while water sorts material by weight and size -- demonstrates genuine understanding.

Periglacial Environments

Periglacial environments are cold but not permanently glaciated. They are characterised by permafrost -- ground that remains at or below 0 degrees Celsius for at least two consecutive years.

Types of Permafrost

• Continuous permafrost -- Found in the coldest regions (mean annual temperature below -5 degrees Celsius). Permafrost extends unbroken beneath the surface and can reach depths of several hundred metres. Found in northern Siberia, Arctic Canada, and northern Alaska.
• Discontinuous permafrost -- Found in slightly warmer regions (-1 to -5 degrees Celsius mean annual temperature). Permafrost is present in most areas but absent beneath lakes, rivers, and south-facing slopes.
• Sporadic permafrost -- Found at the margins of periglacial zones (0 to -1 degrees Celsius mean annual temperature). Permafrost occurs in scattered patches, typically on north-facing slopes and in sheltered hollows.

The Active Layer

The active layer is the upper portion of ground above the permafrost that thaws in summer and refreezes in winter. Its depth varies from a few centimetres in the high Arctic to several metres in warmer periglacial areas. The active layer is where most periglacial processes operate.

Periglacial Processes

• Frost heave -- When water in the soil freezes, it expands and pushes the ground surface upward. Larger particles are pushed to the surface preferentially because ice lenses form beneath them, a process that contributes to patterned ground formation.
• Solifluction -- In summer, the active layer thaws and becomes saturated because the underlying permafrost prevents drainage. The waterlogged soil flows slowly downhill under gravity, even on very gentle slopes. Solifluction creates lobed, terraced slopes and is one of the most widespread periglacial processes.
• Frost shattering (freeze-thaw weathering) -- Repeated freezing and thawing of water in rock crevices breaks up exposed rock, producing angular debris. This creates extensive scree slopes and blockfields in periglacial environments.

Periglacial Landforms

• Patterned ground -- Sorted circles, polygons, and stripes formed by frost heave pushing larger stones to the surface and outward. On flat ground these form circles and polygons; on slopes they are elongated into stripes. Patterned ground is found extensively in Svalbard and across the Arctic tundra.
• Pingos -- Dome-shaped mounds with a core of ice, rising up to 50 metres above the surrounding terrain. Open-system pingos form in discontinuous permafrost where groundwater is forced upward and freezes. Closed-system pingos form in continuous permafrost when a lake drains and the underlying talik refreezes. The Mackenzie Delta in Canada has over 1,300 pingos.
• Ice wedges -- V-shaped wedges of ice that form when the ground cracks in extreme cold, and water fills and freezes in the crack. Over hundreds of years, the process repeats and the wedge grows. Ice wedge polygons are visible in aerial photographs across Siberia and northern Alaska.
• Thermokarst -- An irregular, hummocky landscape of subsidence hollows, thaw lakes, and collapsed ground formed by the melting of ground ice. Thermokarst is increasingly widespread as a result of climate change, which is warming permafrost regions faster than the global average.

Climate Change and Periglacial Areas

Periglacial environments are acutely vulnerable to climate change. Arctic regions are warming at two to three times the global average rate -- a phenomenon known as Arctic amplification. As permafrost thaws, infrastructure built on frozen ground subsides and collapses. Roads, pipelines, and buildings across Alaska and Siberia are already suffering damage. There are also serious environmental consequences: thawing permafrost releases methane and carbon dioxide stored in frozen organic matter, creating a positive feedback loop that accelerates global warming. Some estimates suggest that permafrost stores approximately 1,500 GtC -- roughly twice the amount currently in the atmosphere.

Case Studies

Strong case study use is essential for this topic. You need to know at least one example for each of the following:

A UK Glaciated Landscape

The Lake District is a classic choice. The area was heavily glaciated during the Pleistocene, and the landforms are textbook examples: Helvellyn has a corrie (Red Tarn), an arete (Striding Edge), and evidence of a former glacial trough. Windermere and Wastwater are ribbon lakes. Drumlins are found in the lowlands to the south. Alternatively, Snowdonia provides equally strong examples -- Cwm Idwal is one of the most studied corries in the UK, and the Nant Ffrancon valley is a clear glacial trough.

An Active Glacial Environment

Alpine glaciers such as the Mer de Glace (Mont Blanc) or the Rhone Glacier provide evidence of ongoing glacial retreat, changes to the glacial budget, and the impact of climate change on glacial systems. Svalbard offers examples of polythermal glaciers, surging glaciers, and the interaction between glacial and periglacial processes. For either case, know specific data on rates of retreat and changes in glacier volume.

A Periglacial Environment

Alaska -- particularly the North Slope and the area around Barrow (Utqiagvik) -- provides evidence of continuous permafrost, ice wedge polygons, thermokarst, and the impact of climate change on permafrost infrastructure. Siberia -- especially the Yakutia region -- offers dramatic examples of thermokarst, including the Batagaika crater, one of the largest permafrost thaw features on Earth.

Exam Technique for Glacial Systems Questions

Annotated Diagrams

Annotated diagrams are particularly valuable in this topic. Examiners reward clear, labelled diagrams that show processes at work. Practise drawing:

• A cross-section of a corrie showing the backwall, overdeepened floor, lip, rotational movement, plucking, abrasion, and freeze-thaw weathering.
• A cross-section of a U-shaped valley showing truncated spurs, the flat floor, steep sides, and a hanging valley with a waterfall.
• A plan view and cross-section of a roche moutonnee showing the smooth stoss side (abrasion) and jagged lee side (plucking), with an arrow indicating ice flow direction.
• A diagram showing moraine types in relation to a glacier -- lateral, medial, terminal, and ground moraine.
• A cross-section of a drumlin showing the blunt stoss end and tapered lee end.

A well-annotated diagram can communicate the same information as a full paragraph of text in a fraction of the time. In a timed exam, this is a significant advantage.

Linking Processes to Landforms

The most common weakness examiners report in glacial systems answers is description without explanation. Naming a landform and listing its features is not enough -- you must explain the processes that created it. For every landform, be able to identify the specific erosion or deposition process, explain how the process operates, and connect the process to the resulting shape.

For example, do not simply state that "a corrie has a steep backwall." Explain that freeze-thaw weathering shatters rock on the backwall, the debris falls onto the glacier and is removed, and over time this steepens the backwall through a combination of weathering and the removal of loosened material.

20-Mark Essays

For 20-mark essays on this topic, you are likely to be asked to evaluate the significance of different processes, assess the impact of climate change on glacial systems, or discuss the extent to which glacial landforms are the product of erosion rather than deposition. Structure your answer with a clear argument, use case study evidence throughout -- not just in one paragraph at the end -- and reach a substantiated conclusion. The best answers recognise that glacial landscapes are the product of multiple interacting processes rather than a single dominant one.

Prepare with LearningBro

If you are studying Glacial Systems and Landscapes, structured revision with targeted practice questions will help you embed the material and develop your exam technique:

• AQA A-Level Geography: Glacial Systems and Landscapes -- topic-specific revision covering the glacial budget, processes, landforms of erosion and deposition, and periglacial environments.
• AQA A-Level Geography: Coastal and Glacial Systems in Depth -- deeper coverage of both optional Paper 1 topics, with comparative questions and extended practice.
• AQA A-Level Geography: Exam Preparation -- full exam technique practice across all Paper 1 and Paper 2 topics, including 9-mark and 20-mark essay practice.
• AQA A-Level Geography Revision Guide -- our comprehensive guide covering the full AQA A-Level Geography specification, including all compulsory and optional topics.

Combine these resources with past-paper practice using official AQA mark schemes, and you will develop both the subject knowledge and the exam skills needed to achieve a strong grade. Focus on understanding the system -- once the glacial system makes sense, the processes and landforms follow naturally.