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G27: Glacial Processes and Landforms
FoundationHigherAQAEdexcelOCREduqasCCEA
Freeze-thaw weathering, glacial erosion processes (abrasion and plucking), and glacial landforms including corries, arêtes, pyramidal peaks, truncated spurs, glacial troughs, ribbon lakes, erratics, drumlins and moraine.
❄️ Freeze-Thaw Weathering
Definition: Freeze-thaw weathering (also called frost shattering or frost wedging) is a mechanical weathering process that breaks rock apart when water repeatedly freezes and thaws in cracks and joints.
Freeze-Thaw Process:
1. Water enters cracks and joints in the rock during the day or in warmer conditions
2. Temperatures drop below 0°C and the water freezes
3. Water expands by approximately 9% when it freezes, exerting pressure on the rock
4. The freeze-thaw cycle repeats, gradually widening the crack
5. Eventually, angular rock fragments break off and accumulate as scree at the foot of the slope
Most effective in areas where temperatures frequently cross 0°C (e.g., mountain environments)
Produces angular, sharp-edged rock fragments (unlike rounded river pebbles)
Accumulated debris at the base of cliffs is called scree or talus
Essential process in supplying rock debris for glaciers to erode and transport
Example: Scree Slopes in the Lake District
The Lake District's fells show extensive scree slopes, particularly beneath cliffs of volcanic rock. Screes on peaks like Scafell Pike and Great Gable are composed of angular fragments created by freeze-thaw weathering. During the last Ice Age, these processes were even more intense, but freeze-thaw still operates today during winter cold spells.
⛏️ Glacial Erosion Processes
Key Concept: Glaciers erode the landscape through two main processes: abrasion and plucking. These work together to create distinctive glaciated landforms. The rate of erosion depends on the glacier's velocity, thickness, and the amount of debris it carries.
Abrasion
Debris frozen into the base of the glacier acts like sandpaper, scraping and grinding against the bedrock as the glacier moves
Produces smooth, polished rock surfaces with parallel scratches called striations
Most effective when the glacier carries a large load of coarse, hard debris
Creates rock flour (finely ground rock) that gives glacial meltwater its milky appearance
Plucking
Meltwater at the base of the glacier seeps into cracks in the bedrock and refreezes, attaching rock fragments to the glacier
As the glacier moves forward, it pulls (plucks) these frozen-on rock fragments from the bedrock
Most effective on the downstream side of rock obstacles (where ice pressure is released)
Produces jagged, angular rock surfaces, unlike the smooth surfaces from abrasion
Key Fact: Both processes operate together. Plucking loosens rock material, and abrasion uses that material to grind and smooth the bedrock. A glacier with no debris at its base erodes mainly by plucking; a debris-rich glacier erodes mainly by abrasion.
🏔️ Glacial Erosion Landforms
Corries (Cirques/Cwms)
Definition: A corrie is an armchair-shaped hollow high on a mountainside, formed by glacial erosion. It has a steep back wall, a flat or over-deepened floor, and a raised lip of rock at the front.
Corrie Formation:
1. Snow accumulates in a sheltered hollow on the mountainside (a nivation hollow)
2. Over years, snow compacts into firn (névé) and then glacial ice
3. The growing glacier erodes the hollow through freeze-thaw weathering on the back wall and abrasion on the floor
4>Rotational flow (ice moves in a circular pattern) deepens the floor and steepens the back wall
5. When the glacier melts, a corrie remains - often filled with a tarn (corrie lake)
Example: Red Tarn, Lake District
Red Tarn sits in a classic corrie beneath Helvellyn in the Lake District. The steep back wall was created by freeze-thaw weathering and plucking, while the deep basin was carved by rotational abrasion. When the glacier melted, the hollow filled with water to form the tarn. The raised lip of rock at the front of the corrie dams the lake.
Arêtes
An arête is a narrow, knife-edge ridge formed when two corries erode back-to-back on opposite sides of a mountain
As both glaciers erode their respective hollows, the ridge between them becomes progressively narrower and steeper
When three or more corries erode back-to-back around a mountain summit, they create a pyramidal peak (horn)
Example: Striding Edge, Lake District
Striding Edge is a famous arête on Helvellyn in the Lake District. It was formed when two corries - Red Tarn corrie and the corrie on the east side - eroded back-to-back, leaving a sharp, narrow ridge. It is one of the most dramatic ridge walks in England, with steep drops on both sides.
Pyramidal Peaks (Horns)
A pyramidal peak is a pointed mountain summit formed when three or more corries erode back-to-back
The peak becomes progressively more isolated and pointed as the corries enlarge
The most famous example is the Matterhorn in the Swiss Alps
Truncated Spurs
In river valleys, interlocking spurs project from alternate sides of the valley
When a glacier moves through a river valley, it is too wide and rigid to wind around the spurs
Instead, the glacier truncates (cuts off) the ends of the spurs, creating steep, cliff-like faces
Truncated spurs are a key difference between glaciated U-shaped valleys and river V-shaped valleys
🏞️ Glacial Troughs and Ribbon Lakes
Glacial Troughs (U-Shaped Valleys)
Definition: A glacial trough is a wide, steep-sided valley with a flat bottom, formed when a glacier erodes a pre-existing V-shaped river valley into a U-shape. The glacier straightens, widens and deepens the valley.
Rivers create narrow, V-shaped valleys with interlocking spurs
Glaciers are too wide and thick to wind around spurs, so they erode straight through them
Plucking and abrasion steepen the valley sides and flatten the valley floor
The result is a characteristic U-shaped cross-section with steep, straight sides
The valley floor may be over-deepened below sea level (fjords when flooded by the sea)
Ribbon Lakes
Ribbon lakes are long, narrow lakes found in glacial troughs
They form where the glacier over-deepened part of the valley floor more than others
This often occurs where the glacier crossed bands of softer rock or where tributary glaciers joined, increasing ice volume and erosion
When the glacier retreats, these over-deepened sections fill with water
Case Study: Ullswater, Lake District
Ullswater is a classic ribbon lake in the Lake District, approximately 13 km long and 0.75 km wide. It formed in a glacial trough carved by a valley glacier during the last Ice Age. The glacier over-deepened the valley floor, particularly where the ice was thickest or where softer rock was present. When the glacier retreated around 10,000 years ago, the deep trough filled with meltwater and rainwater. Steep, truncated spurs line the valley sides, and hanging valleys (where smaller tributary glaciers joined) can be seen high above the lake.
🪨 Glacial Deposition Landforms
Key Concept: When a glacier melts, it deposits all the material it has been carrying. This material is called glacial till (boulder clay) - an unsorted mixture of rock fragments ranging from clay to boulders. Unlike river deposits, glacial deposits are NOT sorted by size because ice can carry all sizes simultaneously.
Erratics
An erratic is a large rock or boulder that has been transported by a glacier and deposited in an area of different geology
The rock is foreign to the local bedrock, hence "erratic" (out of place)
Erratics can be huge - some weigh thousands of tonnes
They are useful for tracing the direction of ice movement back to their source
Example: The Bowder Stone, Lake District
The Bowder Stone in Borrowdale is one of England's most famous erratics. It is a 2,000-tonne boulder of volcanic rock (andesite) that was carried by a glacier and deposited in an area of different geology. It stands approximately 9 metres high and 15 metres wide. It was transported from the volcanic rocks of the central Lake District and deposited in the valley when the ice melted.
Drumlins
Drumlins are smooth, oval-shaped hills of glacial till, elongated in the direction of ice flow
They have a steep stoss end (facing up-glacier) and a gentle lee end (facing down-glacier)
Typically 10-50 metres high, 100-500 metres long
Form in swarms (drumlin fields / basket of eggs topography)
Formed beneath moving ice, possibly when glaciers overloaded with sediment are forced to deposit
Example: Eden Valley Drumlins, Cumbria
The Eden Valley in Cumbria contains one of England's finest drumlin fields. The drumlins are aligned north-south, showing the direction of ice flow during the last glaciation. They create a distinctive "basket of eggs" landscape visible from the Pennines. Each drumlin is composed of unsorted boulder clay deposited beneath the ice sheet.
Moraine
Type
Location
Description
Lateral moraine
Along the sides of the glacier
Debris that fell onto the glacier from valley sides
Medial moraine
Down the centre of the glacier
Formed where two lateral moraines merge when glaciers join
Terminal moraine
At the furthest point the glacier reached
A ridge of till marking the maximum extent of the glacier
Recessional moraine
Behind the terminal moraine
Ridges deposited during pauses in the glacier's retreat
Ground moraine (till plain)
Across the valley floor
General deposit of till left as the glacier retreats
Push moraine
At the ice front
Material bulldozed forward during a minor ice advance
Key Fact: Terminal moraines are important because they mark the maximum extent of a glacier. By dating terminal moraines, geographers can reconstruct past glaciations and understand how climate has changed. The best-preserved moraines in the UK are in the Lake District and Snowdonia.
❓ Practice Questions
Q1: Explain the process of freeze-thaw weathering. (4 marks)
Q2: Describe how a corrie forms. (4 marks)
Q3: Compare the processes of abrasion and plucking in glacial erosion. (6 marks)
Q4: "Glacial deposition landforms are more important than glacial erosion landforms for understanding past ice movements." To what extent do you agree? (9 marks)
✅ Answers
Freeze-thaw weathering occurs when water enters cracks and joints in rock during warmer conditions (1 mark). When temperatures drop below 0°C, the water freezes and expands by approximately 9%, exerting pressure on the rock (1 mark). Repeated freeze-thaw cycles gradually widen the cracks (1 mark). Eventually, angular rock fragments break off and accumulate as scree at the base of the slope (1 mark).
A corrie begins when snow accumulates in a sheltered hollow on the mountainside (1 mark). The snow compacts into firn and then glacial ice, and the growing glacier begins to erode through abrasion and plucking (1 mark). Rotational flow deepens the floor and steepens the back wall through freeze-thaw weathering and plucking (1 mark). When the glacier melts, the armchair-shaped hollow remains, often filled with a tarn (corrie lake) behind the raised lip of rock at the front (1 mark).
Abrasion occurs when debris frozen into the base of the glacier scrapes and grinds against the bedrock as the ice moves (1 mark), producing smooth, polished surfaces with parallel striations (1 mark). Plucking occurs when meltwater seeps into cracks in the bedrock, refreezes and attaches rock to the glacier, which then pulls fragments away as it moves (1 mark), producing jagged, angular surfaces on the downstream side of obstacles (1 mark). Abrasion is most effective when the glacier carries a large coarse load, while plucking is most effective where there are well-jointed rocks (1 mark). Both processes operate together - plucking loosens material that abrasion then uses to grind the bedrock (1 mark). They create different surface textures: smooth and striated for abrasion, rough and angular for plucking (1 mark).
I agree that deposition landforms are very important for understanding ice movements because moraines directly mark the position of the glacier at different times - terminal moraines show the maximum extent, and recessional moraines show pauses in retreat (1 mark). Erratics can be traced back to their source, revealing the direction of ice flow (1 mark). Drumlins are aligned in the direction of ice movement, showing the path of glaciers across the landscape (1 mark). However, erosion landforms also provide valuable information - corries indicate the presence and altitude of glaciers (1 mark). Arêtes and pyramidal peaks show where multiple glaciers converged (1 mark). U-shaped valleys and truncated spurs reveal the scale and power of the glacier (1 mark). Striations on bedrock show the precise direction of ice movement at that point (1 mark). Both types are complementary - erosion landforms show where ice was active and how powerful it was, while deposition landforms show where ice stopped and what it carried (1 mark). Together, they provide a more complete picture than either alone, but deposition landforms are arguably more useful for mapping ice extent and movement because they leave clearer, more datable evidence (1 mark).
🎯 Exam Tips
Learn the formation sequences step-by-step (especially corries and U-shaped valleys)
Use Lake District examples for every landform - it's the main UK case study area
Always distinguish between erosion landforms (corries, arêtes) and deposition landforms (erratics, moraines, drumlins)
Remember glacial till is UNSORTED - this is a key difference from river deposits
Know all types of moraine and their locations (lateral, medial, terminal, recessional)
Explain the difference between truncated spurs (glaciated) and interlocking spurs (river valleys)
📝 Exam Technique
Geography Exam Tips — Glacial Processes and Landforms:
1. For Glacial Processes and Landforms questions, always name specific case studies with factual detail
2. Use geographical terminology precisely (e.g. specific processes, not vague descriptions)
3. Consider social, economic and environmental perspectives in your evaluations
4. Support your points about Glacial Processes and Landforms with data, statistics or named examples
5. For 'assess' or 'evaluate' questions, reach a clear judgement supported by evidence
⚠️ Common Errors
Watch Out!
Students often write vague answers without specific geographical evidence. Wrong: Writing generalised statements like 'it causes problems'Correct: Using specific data and named examples, e.g. 'the 2010 Haiti earthquake killed over 200,000 people due to poor building quality'
Students often confuse causes and effects. Wrong: Mixing up what caused the event with what resulted from itCorrect: Clearly separate causes (why it happened) from effects (what happened as a result)
Students often describe rather than evaluate. Wrong: Listing strategies without assessing their effectivenessCorrect: Weighing up strengths and weaknesses of each approach and reaching a supported judgement
✍️ Model Answer
Full-Mark Response
6 marks: Explain the key factors affecting glacial processes and landforms.
Glacial Processes and Landforms involves multiple interconnected factors that geographers must understand. The key concepts include the processes that create and change glacial processes and landforms, the impacts on both people and environment, and the strategies used to manage associated challenges. For a comprehensive answer, specific case study evidence should be used throughout, with named examples and data to support each point. Geographical terminology should be used precisely, and the interrelationship between physical and human factors should be demonstrated. Top-level responses evaluate the relative importance of different factors and consider how the situation varies between locations.
Mark scheme: 2 marks for identifying key factors, 2 marks for explaining processes with detail, 2 marks for using specific evidence
📊 AO Deep Dive
Assessment Objective Analysis
AO1 requires knowledge of the key facts and processes related to glacial processes and landforms. AO2 demands understanding of how and why these processes operate, and their implications. AO3 asks you to analyse, evaluate and make judgements — this is where grade 9 answers stand out by weighing up competing perspectives and reaching supported conclusions. AO4 may involve interpreting maps, graphs or data related to this topic. To move from grade 5 to grade 9: use precise geographical terminology, support every point with specific case study evidence, and always evaluate rather than just describe.
