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 erosion processes, 16.3 Glacial Erosion | Physical Geology

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)