Glacial landforms are created by ice caps and glaciers. In mountain regions, gravity causes glaciers to move downslope. They erode mountain slopes and valleys, transport debris, and deposit it where the ice melts. Glacial landforms also occur beneath and upon glaciers, not only on mountain slopes.
Erosional Landforms
Cirque, Arête, and Pyramidal Peak
- Cirque, corrie, or cwm: a steep-walled, bowl-shaped hollow eroded at the head of a mountain glacier.
- Tarn or cirque lake: a lake occupying a cirque after the glacier has melted. A series of lakes connected in steps down a glacial valley is called a paternoster lake system.
- Arête: a sharp, knife-edged ridge formed when two cirques erode backwards on opposite or adjacent sides of a mountain ridge.
- Pyramidal peak or horn: an angular, pyramid-shaped summit formed when three or more cirques erode backwards into a mountain from different sides.
Randkluft, Bergschrund, and Crevasse
- Randkluft: a gap between the head or side of a glacier and the adjacent rock wall, produced as the glacier moves away from the warmer rock face.
- Bergschrund: a large, deep crevasse near the head of a mountain glacier, where moving ice separates from relatively stagnant ice or firn above. It can be a major obstacle to mountaineers.
- Crevasse: a crack or fracture in a glacier caused by stresses produced as the ice flows over uneven terrain or changes speed.
Glacial Trough, Hanging Valley, and Fjord
- Glacial trough or U-shaped valley: a deep, broad valley with steep sides and a relatively flat floor, created when a large glacier widens and deepens a pre-existing valley through abrasion and plucking.
- Hanging valley: a smaller tributary glacial valley left above the floor of a deeper main trough. Meltwater or a river may descend from it as a waterfall.
- Fjord: a deep, narrow coastal inlet formed when the sea floods a glacial trough. Fjords are especially common along formerly glaciated coasts, including Norway and other parts of Scandinavia.
Roche Moutonnée
A roche moutonnée is an asymmetrical bedrock knob shaped by a moving glacier:
- The up-glacier (stoss) side is smoothed and gently sloping because of abrasion and polishing.
- The down-glacier (lee) side is rough and steep because of plucking.
Crag and Tail
A crag and tail consists of a resistant rock mass and a sheltered, tapering ridge of softer material:
- The crag is the steep, resistant rock on the up-glacier side.
- The tail is the smoother, gentler ridge extending down-glacier, protected from direct erosion by the crag.
Depositional Landforms
Till and Moraines
Till is unsorted sediment transported and deposited directly by glacial ice. When lithified, it forms tillite. A moraine is a ridge or accumulation of glacial debris classified by its position:
| Moraine | Location or origin |
|---|---|
| Lateral moraine | Deposited along the sides of a glacier. |
| Medial moraine | Forms down the centre where the adjacent lateral moraines of two merging glaciers unite. |
| Terminal or end moraine | Marks the glacier’s farthest advance at its terminus. |
| Recessional moraine | An end moraine formed during a temporary pause in glacial retreat. |
| Ground moraine | A widespread blanket of till deposited beneath a glacier; unlike terminal and recessional moraines, it need not form a prominent ridge. |
Outwash Plain
An outwash plain is a broad, relatively level surface beyond a glacier’s terminus, formed by layers of sand and gravel deposited by glacial meltwater. These sediments are fluvioglacial: transported and sorted by flowing meltwater.
Associated landforms include:
- Drumlin: a streamlined, elongated hill composed mainly of till or boulder clay. It typically has a steeper up-glacier end and a gentler, tapered down-glacier end. Groups of drumlins are sometimes described as a basket-of-eggs topography.
- Esker: a long, narrow, winding ridge of stratified sand and gravel deposited by a meltwater stream flowing within or beneath a glacier.
- Kame: a small, irregular mound or hill of sand and gravel deposited by meltwater in contact with glacier ice.
- Kettle: a depression formed when a detached block of buried ice melts and the overlying sediment collapses. If filled with water, it forms a kettle lake.
- Knob-and-kettle topography: an irregular landscape of alternating depositional mounds (knobs) and depressions (kettles).