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Glacial Deposition Landforms

Glacial landforms resulting from transportation and deposition – erratics, drumlins, types of moraine.

Key words

  1. Drumlin - A hill made of glacial till deposited by a moving glacier, usually elongated or oval in shape, with the longer axis parallel to the former direction of ice.
  2. Erratics - Rocks which have been transported and deposited by a glacier some distance from their source region.
  3. Moraine  - Frost-shattered rock debris and material eroded from the valley floor and sides, transported and deposited by glaciers.

Landforms created by glacial deposition are often found in much lower altitudes in lower valleys.  They are found in areas where the temperature is warmer so the ice melts and loses its capacity to carry material. The major features include erratics, drumlins and different types of moraine.

Erratics are large boulders that sit on top of a different type of rock on the landscape.  They have often been transported huge distances by the ice and deposited far from their bedrock of origin.  Ice transported boulders are similar, but are still found on their bedrock of origin.  The Bowder Stone in Borrowdale, Cumbria is a 2,000 ton erratic thought to originate in Scotland.

Boweder Stone
The Bowder Stone by Shaun Ferguson

Moraine – This is the material produced by glacial erosion.  The material tends to be unsorted (it contains really huge boulders and at the same time a fine powder called glacial flour).  It also tends to be very angular, as the processes that form the material involve freezing and shattering.

Lateral and medial moraines
Aerial view of medial glacier moraines, Nuussuaq Peninsula, Greenland. By Algkalv (Own work)


There are different types of moraine including:

  • Ground moraine - which is moraine spread all over the ground as a glacier retreats up valley in warmer times
  • Terminal moraine - which are rocks deposited in a ridge at the maximum advance of the ice
  • Lateral Moraine which are ridges of moraine that come from the valley sides and run parallel to those valley sides
  • Medial Moraine - these are a ridge of rocks running down the middle of a valley formed by 2 lateral moraines from 2 glaciers coming together.
  • Recessional moraine – these often run parallel to terminal moraines and these ridges of material mark the retreat of a glacier.  Each recessional moraine marks a point where the ice has been static long enough in the glaciers retreat for material to build up.

Moraines in New Zealand

Moraines in New Zealand


Drumlins
A drumlin is a hill of compact, unsorted glacial till, usually oval in shape, with the long axis showing the former glacial motion.
The most identifying characteristic of drumlins are their shape, resembling an inverted spoon with its steep slope facing the direction from which the ice advances. Drumlins can be up to 7 km in length, 2 km in width and 30 m in height.
They are thought to form where material is deposited underneath a glacier as ground moraine.  This material is then shaped into the drumlin shape as the ice advances or retreats.  Running water under the ice could also play a role in helping shape the drumlin. 

Drumlin formation

 

 

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