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Glacial landform

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Glacial landform

Antique postcard shows rocks scarred by glacial erosion.
Yosemite Valley from an airplane, showing the U-shape
Glacially-plucked granitic bedrock near Mariehamn, Åland Islands.

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 very old fossil glacial landforms.

Erosional landforms

Erosional landforms
As the glaciers expanded, due to their accumulating weight of snow and ice, they crush and abrade scoured surface rocks and bedrock. The resulting erosional landforms include striations, cirques, glacial horns, arêtes, trim lines, U-shaped valleys, roches moutonnées, overdeepenings and hanging valleys.
  • Cirque: Starting location for mountain glaciers
  • Cirque stairway: a sequence of cirques
  • U-shaped valley: U-shaped valleys are created by mountain glaciers. When filled with ocean water so as to create an inlet, these valleys are called fjords.
  • Arête: spiky high land between two glaciers, if the glacial action erodes through, a spillway (or col) forms.

Depositional landforms

Depositional landforms

Later, when the glaciers retreated leaving behind their freight of crushed rock and sand (glacial drift), they created characteristic depositional landforms. Examples include glacial moraines, eskers, and kames. Drumlins and ribbed moraines are also landforms left behind by retreating glaciers. 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 sub-glacial stream.
  • Kame: Irregularly shaped mound.
  • Moraine: Feature can be terminal (at the end of a glacier), lateral (along the sides of a glacier), or medial (formed by the emerger of lateral moraines from contributary glaciers).
  • Outwash fan: Braided stream flowing from the front end of a glacier.

Glacial lakes and ponds

Lakes and ponds may also be caused by glacial movement. Kettle lakes form when a retreating glacier leaves behind an underground or surface chunk of ice that later melts to form a depression containing water. Moraine-dammed lakes occur when glacial debris dam a stream (or snow runoff). Jackson Lake and Jenny Lake in Grand Teton National Park are examples of moraine-dammed lakes, though Jackson Lake is enhanced by a man-made dam.

  • Kettle lake: Depression, formed by a block of ice separated from the main glacier, in which the lake forms.
  • Tarn: A lake formed in a cirque by overdeepening.
  • Paternoster lake: A series of lakes in a glacial valley, formed when a stream is dammed by successive terminal moraines left by an advancing or retreating glacier.
  • Glacial Lake: A lake that formed between the front of a glacier and the last terminal moraine.

Ice Features

Apart from the landforms left behind by glaciers, glaciers themselves may be striking features of the terrain, particularly in the polar regions of the earth. Notable examples include valley glaciers where glacial flow is restricted by the valley walls, crevasses in the upper section of glacial ice, and icefalls—the ice equivalent of waterfalls.

See also

External links

  • 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
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