7.2 Glacial erosion processes and landforms

Glaciers are nature's bulldozers, carving and shaping landscapes with incredible force. Through abrasion and plucking, 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.

Subglacial meltwater 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

Top images from around the web for Mechanical and Chemical Processes

• 

  TC - Formation of ribbed bedforms below shear margins and lobes of palaeo-ice streams View original

  Is this image relevant?

• 

  TC - Glacial sedimentation, fluxes and erosion rates associated with ice retreat in Petermann ... View original

  Is this image relevant?

• 

  16.3 Glacial Erosion – Physical Geology – 2nd Edition View original

  Is this image relevant?

• 

  TC - Formation of ribbed bedforms below shear margins and lobes of palaeo-ice streams View original

  Is this image relevant?

• 

  TC - Glacial sedimentation, fluxes and erosion rates associated with ice retreat in Petermann ... View original

  Is this image relevant?

1 of 3

Top images from around the web for Mechanical and Chemical Processes

• 

  TC - Formation of ribbed bedforms below shear margins and lobes of palaeo-ice streams View original

  Is this image relevant?

• 

  TC - Glacial sedimentation, fluxes and erosion rates associated with ice retreat in Petermann ... View original

  Is this image relevant?

• 

  16.3 Glacial Erosion – Physical Geology – 2nd Edition View original

  Is this image relevant?

• 

  TC - Formation of ribbed bedforms below shear margins and lobes of palaeo-ice streams View original

  Is this image relevant?

• 

  TC - Glacial sedimentation, fluxes and erosion rates associated with ice retreat in Petermann ... View original

  Is this image relevant?

1 of 3

• 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 U-shaped valley 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