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Glacial Moraine

Moraine is material transported by a glacier and then deposited. There are eight types of moraine, six of which form recognisable landforms, and two of which exist only whilst the glacier exists.

The types of moraine that form landforms are Ground, Lateral, Medial, Push, Recessional and Terminal.
The two types only associated with glacial ice are Supraglacial and Englacial moraine.

Ground Moraine
Ground moraine is till deposited over the valley floor. It has no obvious features and is to be found where the glacier ice meets the rock underneath the glacier. It may be washed out from under the glacier by meltwater streams, or left in situ when the glacier melts and retreats.

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Lateral Moraine
Lateral moraine forms along the edges of the glacier. Material from the valley walls is broken up by frost shattering and falls onto the ice surface. It is then carried along the sides of the glacier. When the ice melts it forms a ridge of material along the valley side.

Lateral moraine
An abandoned lateral moraine left when the glacier retreated.

In the photograph above, the lateral moraine ridge marks the edge of a past glacier of much greater proportions than the one existing today. The present glacier can be seen top left of the image, and is clearly much reduced in size.

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Medial Moraine
Medial moraine is formed from two lateral moraines. When two glaciers merge, the two edges that meet form the centre line of the new glacier. In consequence two lateral moraines find themselves in the middle of the glacier forming a line of material on the glacier surface. The existence of a medial moraine is evidence that the glacier has more than one source. When the ice melts it forms a ridge of material along the valley centre.

Medial moraine
Medial moraine visible as a dark line along the centre of the glacier. Wide lateral moraines can be seen on either side.

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Push Moraine
Push moraines are only formed by glaciers that have retreated and then advance again. The existence of a push moraine is usually evidence of the climate becoming poorer after a relatively warm period. Material that had already been deposited is shoved up into a pile as the ice advances, and because most moraine material was deposited by falling down not pushing up, there are characteristic differences in the orientation of rocks within a push moraine. A key feature enabling a push moraine to be identified is individual rocks that have been pushed upwards from their original horizontal positions.

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Recessional Moraine
Recessional moraines form at the end of the glacier so they are found across the valley, not along it. They form where a retreating glacier remained stationary for sufficient time to produce a mound of material. The process of formation is the same as for a terminal moraine, but they occur where the retreating ice paused rather than at the furthest extent of the ice.

Recessional moraine
A recessional moraine in the French Alps. Scale is provided by the two climbers in the centre of the image.

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Terminal Moraine
The terminal moraine forms at the snout of the glacier. It marks the furthest extent of the ice, and forms across the valley floor. It resembles a large mound of debris, and is usually the feature that marks the end of unsorted deposits and the start of fluvially sorted material.

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Supraglacial Moraine
Supraglacial moraine is material on the surface of the glacier, including lateral and medial moraine, loose rock debris and dust settling out from the atmosphere.

Supraglacial moraine
Supraglacial moraine with underlying ice visible where a surface stream has cut down through the moraine

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Englacial Moraine
Englacial moraine is any material trapped within the ice. It includes material that has fallen down crevasses and the rocks being scraped along the valley floor.

Supraglacial moraine falling down a crevasse and becoming englacial moraine

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Last update to this statement was on: February 23, 2006

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