Glaciers are powerful agents of erosion, shaping landscapes through processes like abrasion and plucking. These icy giants carve out distinctive features in mountainous regions, from bowl-shaped cirques to knife-edge arêtes and pyramid-like horns.

As glaciers move, they deposit material, creating various landforms. Moraines, eskers, and drumlins are just a few examples of the diverse terrain left behind. These glacial deposits provide clues about past ice movements and climate changes.

Glacial Erosion Processes

Glacial erosion processes

• Abrasion
  • Rock fragments embedded in glacial ice scrape against bedrock creating smooth, polished surfaces (glacial polish)
  • Produces fine-grained sediment called rock flour giving glacial meltwater its characteristic milky appearance
  • Striations form parallel grooves in bedrock indicating ice flow direction
• Plucking
  • Glaciers freeze onto loose rock fragments and tear them away as ice moves downslope
  • Meltwater refreezes in cracks and crevices expanding and loosening rocks (frost wedging)
  • Results in angular, jagged rock fragments transported within or on top of glacier
• Glacial quarrying
  • Large-scale removal of bedrock blocks by glacier
  • Occurs in areas of weakness in bedrock (joints, faults)
  • Creates steep-sided valleys and fjords
• Meltwater erosion
  • Streams flowing on, within, or beneath glacier erode rock and sediment
  • Forms subglacial channels and potholes
  • Contributes to formation of eskers and kames

Alpine glacier erosional landforms

• Cirques
  • Bowl-shaped depressions carved into mountainsides by freeze-thaw weathering and plucking
  • Often contain small lakes called tarns after glacial retreat
  • Accumulation zone where snow collects and compresses into glacial ice
• Arêtes
  • Sharp, knife-edge ridges between adjacent cirques formed by erosion of two glaciers flowing in opposite directions
  • Can form when cirque headwalls erode back to meet
  • Examples include Crib Goch in Snowdonia and Striding Edge in the Lake District
• Horns
  • Pyramid-shaped peaks formed when three or more cirques erode towards a central point
  • Created by the intersection of multiple arêtes
  • Famous examples include Matterhorn (Switzerland) and K2 (Pakistan/China border)
• U-shaped valleys
  • Formed as glaciers deepen and widen pre-existing V-shaped river valleys
  • Characterized by steep sides and flat bottoms
  • Examples include Yosemite Valley (California) and Lauterbrunnen Valley (Switzerland)
• Hanging valleys
  • Smaller tributary valleys left "hanging" above main glacial valley
  • Form when main glacier erodes more deeply than tributary glaciers
  • Often result in waterfalls where tributary streams enter main valley (Bridalveil Fall in Yosemite)
• Glacial troughs
  • Deep, straight valleys carved by glaciers, often below sea level
  • Can become fjords when flooded by seawater after glacial retreat
  • Examples include Sognefjord (Norway) and Milford Sound (New Zealand)

Glacial depositional features

• Moraines
  • Ridges or mounds of unsorted glacial debris (till) deposited directly by glacier
  • Terminal moraines mark farthest extent of glacier advance
  • Lateral moraines form along sides of glaciers
  • Medial moraines result from merging of two lateral moraines when glaciers converge
  • Ground moraines are flat or gently undulating layers of till deposited as glacier retreats
• Eskers
  • Long, winding ridges of stratified sand and gravel formed by streams flowing through tunnels beneath or within glaciers
  • Can extend for many kilometers and reach heights of 100 meters
  • Provide important habitat and travel routes in otherwise flat landscapes
• Drumlins
  • Elongated hills composed of glacial till with streamlined shape and blunt end facing direction of ice flow
  • Often occur in groups called drumlin fields
  • Examples include drumlins in upstate New York and County Down, Ireland
• Erratics
  • Large boulders transported by glaciers and deposited far from their source
  • Can be used to trace glacier movement and determine ice flow direction
  • Plymouth Rock (Massachusetts) is a famous glacial erratic
• Kettle lakes
  • Formed when buried ice blocks melt, leaving depressions that fill with water
  • Often found in outwash plains or end moraine complexes
  • Examples include lakes in Minnesota (Land of 10,000 Lakes) and Finland
• Kames
  • Irregular mounds of stratified sand and gravel deposited by meltwater at glacier margin
  • Often associated with kettles in "kame and kettle" topography
  • Provide important aquifers in glaciated regions

Alpine vs continental glacier landforms

• Alpine glacier landforms
  • Typically found in mountainous regions at high elevations or latitudes
  • Create features like cirques, arêtes, and horns through erosion of mountain peaks
  • U-shaped valleys and hanging valleys characterize lower elevations
  • Lateral and terminal moraines common at valley mouths
• Continental glacier landforms
  • Affect much larger areas, often entire regions or continents
  • Create extensive till plains and outwash plains covering vast areas
  • Form drumlins, eskers, and kettle lakes across low-relief landscapes
  • Produce large end moraines marking former ice sheet boundaries (Great Lakes region)
• Shared features
  • Both types create striations and grooves on bedrock indicating ice flow direction
  • Erratics (large transported boulders) deposited by both alpine and continental glaciers
  • Glacial lakes form in landscapes shaped by either type (proglacial, kettle, finger lakes)
• Scale differences
  • Alpine glaciers create localized, dramatic topography in mountain ranges
  • Continental glaciers shape entire regions, creating subtle but extensive landforms
  • Continental glaciers generally produce larger versions of some alpine glacier features (moraines, outwash plains)