thumb|right|Antique postcard shows rocks scarred by glacial erosion

thumb|[[Yosemite Valley from an airplane, showing the "U" shape]]

thumb|right|[[Plucking (glaciation)|Glacially plucked granitic bedrock near Mariehamn, Åland]]

thumb|[[Kamenitsa Peak (Pirin)|Kamenitsa Peak erosion in Pirin mountain, Bulgaria]]

Glacial landforms are landforms created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations. Some areas, like Fennoscandia and the southern Andes, have extensive occurrences of glacial landforms; other areas, such as the Sahara, display rare and very old fossil glacial landforms.

Erosional landforms

thumb|Erosional landformsAs the glaciers expand, due to their accumulating weight of snow and ice they crush, abrade, and scour surfaces such as rocks and bedrock. The resulting erosional landforms include striations, cirques, glacial horns, arêtes, trim lines, U-shaped valleys, roches moutonnées, overdeepenings and hanging valleys.

  • Striations: grooves and indentations in rock outcrops, formed by the scraping of small sediments on the bottom of a glacier across the Earth's surface. The direction of striations display the direction the glacier was moving.
  • Cirque: Starting location for mountain glaciers, leaving behind a bowl shaped indentation in the mountain side once the small glacier has melted.(add geology book citation already in the article)
  • Roche moutonnée
  • Nunatak

Depositional landforms

thumb|Depositional landforms

Later, when the glaciers retreated leaving behind their freight of crushed rock and sand (glacial drift), they created characteristic depositional landforms. Depositional landforms are often made of glacial till, which is composed of unsorted sediments (some quite large, others small) that were eroded, carried, and deposited by the glacier some distance away from their original rock source. Examples include glacial moraines, eskers, and kames. Drumlins and ribbed moraines are also landforms left behind by retreating glaciers. Many depositional landforms result from sediment deposited or reshaped by meltwater and are referred to as fluvioglacial landforms. Fluvioglacial deposits differ from glacial till in that they were deposited by means of water, rather than the glacial itself, and the sediments are thus also more size sorted than glacial till is. The stone walls of New England contain many glacial erratics, rocks that were dragged by a glacier many miles from their bedrock origin.

  • Esker: Built up bed of a subglacial stream, forming small, string-like mounds left behind as a glacier retreats.

The idea of elevated flat surfaces being shaped by glaciation—the glacial buzzsaw effect—has been rejected by various scholars. In the case of Norway the elevated paleic surface has been proposed to have been shaped by the glacial buzzsaw effect. However, this proposal is difficult to reconcile with the fact that the paleic surfaces consist of a series of steps at different levels. The elevated plains of West Greenland are also unrelated to any glacial buzzsaw effect.

The Gulf of Bothnia and Hudson Bay, two large depressions at the centre of former ice sheets, are known to be more the result of tectonics than of any weak glacial erosion.

See also

  • Fluvioglacial landform
  • Glaciofluvial deposits
  • Limno-glacial

References

  • Illustrated glossary of alpine glacial landforms
  • Landforms of glaciation
  • Diagram illustrating mechanisms of glacial landforms in The Ice Melts: Deposition on page 6 of "Pennsylvania and the Ice Age" published 1999 by PA DCNR Bureau of Topographic and Geologic Survey