7.2 Glacial erosion processes and landforms
3 min read•july 30, 2024
Glaciers are nature's bulldozers, carving and shaping landscapes with incredible force. Through and , they create unique landforms like cirques, U-shaped valleys, and glacial horns. These processes transform entire mountain ranges and leave lasting impacts on the Earth's surface.
plays a crucial role in glacial erosion, enhancing the glacier's ability to sculpt the land. It creates features like potholes and eskers, and forms subglacial lakes. The combined action of ice and water results in dramatic landscape modifications that continue to influence modern environments.
Glacial Erosion Processes
Mechanical and Chemical Processes
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- Glacial erosion wears away and reshapes underlying bedrock and sediment through mechanical and chemical processes
- Effectiveness depends on factors
- Ice velocity
- Ice thickness
- Ice temperature
- Properties of underlying bedrock
- Erosion rates vary significantly
- Cold-based glaciers: less than 0.1 mm/year
- Warm-based, fast-flowing glaciers: over 10 mm/year
Abrasion and Plucking
- Abrasion scours glacier bed with rock fragments embedded in ice base
- Results in striations and polished surfaces (glacial polish)
- Plucking removes rock fragments frozen to glacier bed as ice moves
- Creates jagged surface (roche moutonnée)
- Quarrying removes large bedrock blocks facilitated by pre-existing fractures
- Forms steep cliff faces (headwalls)
Erosional Landforms
Cirques and Arêtes
- Cirques form bowl-shaped depressions carved into mountainsides
- Shaped by combination of plucking and abrasion
- Involve nivation process where snow accumulates in pre-existing depressions
- Arêtes create sharp, knife-edge ridges between adjacent cirques
- Form when two cirques erode headward into a mountain
- Examples include Crib Goch in Snowdonia, Wales
Glacial Valleys and Associated Features
- U-shaped valleys (glacial troughs) form by widening and deepening pre-existing river valleys
- Ice erodes both valley floor and walls, unlike rivers which primarily erode downward
- Examples include Yosemite Valley, California
- Hanging valleys suspend smaller tributary valleys above main floor
- Result from differential erosion rates between main and tributary glaciers
- Create waterfalls where tributary streams flow into main valley (Bridalveil Fall, Yosemite)
- Glacial horns form sharp, pyramidal peaks when three or more cirques erode headward
- Famous example (Matterhorn, Swiss Alps)
Subglacial Meltwater's Role
Erosional Processes and Features
- Subglacial meltwater enhances glacial erosion
- Facilitates sediment transport
- Increases effectiveness of abrasion and plucking
- Creates distinctive erosional features
- Potholes: cylindrical holes drilled by swirling water and sediment
- Flutes: elongated ridges parallel to ice flow
- P-forms: smooth, undulating rock surfaces sculpted by pressurized water flow
- Tunnel valleys form long, overdeepened troughs beneath ice sheets
- Carved by pressurized subglacial meltwater
- Often follow pre-existing bedrock weaknesses
- Examples found in northern Europe and North America
Depositional Features and Hydrological Impacts
- Eskers create sinuous ridges of glaciofluvial sediment
- Deposited by meltwater streams within or beneath glaciers
- Represent preserved subglacial drainage channels
- Examples found in Finland and Canada
- Subglacial lakes form by meltwater accumulation beneath ice sheets
- Influence ice dynamics and erosional processes at glacier bed
- Lake Vostok in Antarctica largest known subglacial lake
- Interaction between meltwater and sediment forms streamlined subglacial bedforms
- Drumlins: elongated hills aligned parallel to ice flow
- Mega-scale glacial lineations: extremely long parallel ridges
Glacial Erosion's Impact on Landscapes
Landscape Modification and Denudation
- Glacial erosion primarily shapes alpine and high-latitude landscapes
- Creates distinctive landforms not found in non-glaciated regions
- Alters pre-existing fluvial drainage patterns
- Develops new watershed boundaries and river systems
- Examples include the Great Lakes basin in North America
- Contributes to mountain range denudation
- Glaciers erode mountains up to 10 times faster than other erosional processes
- Varies with latitude, elevation, and climate
- Most pronounced in high mountain ranges (Himalayas) and polar regions (Greenland)
Long-term Landscape Evolution
- Creates overdeepened basins becoming lakes after glacier retreat
- Influences hydrology and ecology of deglaciated landscapes
- Examples include the lakes of the European Alps and Patagonia
- Interacts with other geomorphic agents to shape complex landscape systems
- Mass wasting (landslides, rockfalls)
- Fluvial erosion (river incision, sediment transport)
- Legacy of past glacial erosion continues to influence modern landscapes
- Affects sediment supply to rivers and coasts
- Impacts slope stability in mountainous regions
- Influences ecosystem development and biodiversity patterns
Key Terms to Review (23)
Abrasion: Abrasion is the process of wearing away surfaces through friction or impact caused by particles or other materials. This physical weathering mechanism plays a significant role in shaping landscapes and is a key component in various erosional processes, influencing landforms and sedimentation across different environments.
Arete: Arete is a sharp, knife-edged ridge formed by glacial erosion, often found between two cirques or glacial valleys. These stunning landforms are created as glaciers carve away the surrounding rock, leading to steep, rugged profiles that rise prominently in the landscape. Aretes can serve as impressive natural boundaries and are often seen in mountain ranges that have experienced significant glaciation.
Basal Sliding: Basal sliding is the movement of a glacier over its bed, facilitated by a thin layer of meltwater that reduces friction between the glacier and the underlying ground. This process is crucial for understanding how glaciers move and change shape, as it allows large masses of ice to flow more easily across varying terrains. Basal sliding contributes significantly to the dynamics of glaciers and plays a vital role in glacial erosion, shaping the landscape and forming distinctive landforms.
Cirque: A cirque is a bowl-shaped, amphitheater-like depression formed by glacial erosion at the head of a glacier. These unique landforms are typically characterized by steep, rocky walls and are often filled with a lake or snow. Cirques are significant because they serve as important indicators of past glacial activity and help illustrate the powerful processes of glacial erosion and landscape transformation.
Drumlin: A drumlin is a streamlined, elongated hill formed by glacial deposits, typically composed of till, that occurs in a landscape shaped by past glacial activity. These features are often found in groups, indicating the direction of glacial movement and serving as important indicators of the dynamics of ice sheets and the sedimentary processes involved in glacial environments.
Esker: An esker is a long, narrow ridge of sand and gravel that is formed by glacial meltwater. These formations are created as streams of meltwater flow beneath a glacier, depositing sediment as they move, eventually leading to the formation of these distinctive landforms once the glacier retreats. Eskers often indicate the direction of glacial flow and can provide insights into past glacial environments.
Flute: A flute is a streamlined, elongated feature created by glacial erosion, typically found in glaciated landscapes. These formations result from the movement of glaciers, which carve into the underlying rock and sediment, creating a distinctive shape that resembles a flute or a spoon. Flutes are important indicators of past glacial activity and help geologists understand the dynamics of glacier flow and the landscape's evolution.
Glacial horn: A glacial horn is a sharp, pyramid-like peak formed by the erosion of a mountain by multiple glaciers converging from different sides. This unique landform showcases the intense erosive power of glaciers, as they carve out valleys and peaks through processes like plucking and abrasion, leading to the distinctively pointed shape characteristic of glacial horns. Such formations are often found in rugged mountainous regions where glaciers have shaped the landscape over long periods.
Glacial Scouring: Glacial scouring is a process of erosion that occurs when a glacier moves across the landscape, scraping and grinding the underlying rock and soil as it advances. This intense abrasion shapes the land, creating unique landforms and features such as striations, polished surfaces, and depressions known as glacial troughs. The extent of glacial scouring can reveal the historical movements of glaciers and their impact on the surrounding environment.
Internal deformation: Internal deformation refers to the process by which glaciers change shape and move due to the internal stress caused by their own weight and the temperature of the ice. This phenomenon is crucial in understanding how glaciers flow and respond to environmental changes, as it influences both their dynamics and the processes of erosion and sediment transport beneath them.
John Tyndall: John Tyndall was a 19th-century Irish physicist best known for his work on the absorption of infrared radiation by gases, particularly water vapor and carbon dioxide. His experiments laid the groundwork for understanding the greenhouse effect and how certain gases contribute to climate change, which has significant implications for glacial erosion processes and landforms over time.
Louis Agassiz: Louis Agassiz was a Swiss-American geologist and naturalist who made significant contributions to the study of glaciology and paleontology during the 19th century. He is best known for his pioneering research on glaciers and their impact on the landscape, laying the foundation for understanding glacial erosion processes and the resulting landforms shaped by these immense forces of nature.
Mega-scale glacial lineation: Mega-scale glacial lineation refers to large, elongated landforms that are shaped by the movement of glacial ice across the landscape. These features are often found in areas previously covered by thick ice sheets and can extend for several kilometers, showcasing the direction of glacier flow. They provide crucial insights into glacial dynamics, erosion processes, and the geomorphological impact of glaciers on the Earth's surface.
Moraine: A moraine is a landform created from the accumulation of debris, primarily composed of rocks and sediments, that has been transported and deposited by glaciers. Moraines serve as important indicators of past glacial activity and are essential in understanding how glaciers interact with the landscape, shaping it through both erosion and deposition processes.
Outwash: Outwash refers to sediment deposited by meltwater streams flowing from a glacier. This material is typically composed of sand, gravel, and silt that have been transported away from the glacier's terminus, creating a range of landforms such as outwash plains and deltas. The characteristics of outwash help to illustrate the dynamics of glacial erosion processes and how they shape the landscape.
P-form: P-form refers to a specific shape of glacial landform created by the erosion and movement of glaciers. These formations are characterized by their streamlined, teardrop-like shape, which is a result of the glacial flow carving out the landscape, allowing for the efficient transport of sediment. Understanding p-forms is essential to grasp how glaciers interact with the underlying geology and contribute to landscape evolution.
Plucking: Plucking is a glacial erosion process where a glacier removes and incorporates rocks and sediment from the bedrock as it moves. This process occurs when the glacier freezes onto the underlying rock and, as it advances, it pulls pieces of the rock away, effectively eroding the surface. Plucking is crucial in shaping landscapes, contributing to distinctive landforms such as U-shaped valleys and jagged mountain peaks.
Pothole: A pothole is a bowl-shaped depression in the ground caused by the erosion of soil and sediment, typically resulting from the combination of freeze-thaw cycles and water accumulation. In the context of glacial processes, potholes can form when a glacier scours the landscape, creating depressions that can fill with water. These features often indicate the powerful erosive forces glaciers exert on the Earth’s surface.
Subglacial erosion: Subglacial erosion refers to the process by which glaciers erode the underlying bedrock and sediments as they move. This type of erosion occurs beneath the glacier, where the pressure from the ice and the presence of meltwater create conditions that facilitate the wearing away of the landscape. It plays a crucial role in shaping glacial landforms, contributing to features like U-shaped valleys and fjords.
Subglacial meltwater: Subglacial meltwater is water that has melted from the base of a glacier and exists beneath the ice, often creating a dynamic and complex system. This meltwater plays a significant role in glacial movement, erosion processes, and the formation of unique landforms. The interaction between meltwater and the glacier base can influence the rate of glacial retreat, sediment transport, and the development of subglacial features.
Till: Till is a type of unsorted and unstratified glacial sediment that is deposited directly by a glacier as it moves and melts. This material can vary widely in size, from clay to boulders, and serves as a primary indicator of past glacial activity and the processes of glacial erosion. Understanding till is essential for interpreting landforms shaped by glaciers, as it reflects the glacier's movement and the environmental conditions during its advance and retreat.
Tunnel valley: A tunnel valley is a large, often U-shaped depression formed beneath a glacier, typically resulting from the erosion of the substrate by meltwater and sediment transport. These valleys are often found in regions once covered by ice sheets and can exhibit characteristics such as streamlined shapes and distinct longitudinal profiles. They play an important role in understanding glacial processes and landforms, revealing how glaciers interact with their environment during periods of retreat.
U-shaped valley: A U-shaped valley is a distinctive landform created by glacial erosion, characterized by its wide, flat floor and steep, straight sides resembling the letter 'U'. This shape is formed as glaciers move through valleys, carving out the landscape and deepening the valley floor while widening its cross-section. U-shaped valleys often showcase features such as hanging valleys, cirques, and fjords, all indicative of significant glacial activity.