Moraines

Moraines are the piles of dirt and rock that are displaced by a glacier as it moves across the landscape. These debris fields exist in areas that are currently glaciated and in places where glaciers have moved through in the past. Rocks, soil and other geological materials are caught up in the glacial ice or fall onto the surface and are carried through the landscape, eventually being deposited as the glacier melts or as the objects move to the bottom of the ice.

The debris in moraines can be rocks as big as houses or sand-like material. The friction from the ice slowly scraping across the ground makes these rocks, boulders or small gravel bits rounded or angular as they are smoothed out by the constant movement. Debris can also come from the land on the sides of the glacier as the ice scrapes off bits of the valley walls as the glacier moves.

There are many kinds of glacial moraines that form. Moraines are generally classified by where they are located, if there is a current glacier or one that has already melted, or their origins (or a combination of the above).

Moraine in the Ala-Archa Valley, Kirgizia.  Photo: Martin Talbot.

Moraine in the Ala-Archa Valley, Kirgizia. Photo: Martin Talbot.

Lateral moraines

Lateral moraines are ridges of debris that run parallel to the sides of a glacier. This is often accompanied by scraping of the valley sides which means the debris from the moraine creates high ridges above the glacier.

Lateral Moraine, Squamish-Lillooet, British Columbia, Canada.  Photo: Ruth Hartnup

Lateral Moraine, Squamish-Lillooet, British Columbia, Canada. Photo: Ruth Hartnup

Ground moraines

Ground moraines are moraines that form in rolling hills or irregular planes that are left as a glacier retreats. Ground moraines can be deposited in the middle of lateral moraines in the case of many alpine glaciers.

Ground moraine of a former glacier on Bylot Island (Sirmilik National Park, Canada).  Photo: Ansgar Walk.

Ground moraine of a former glacier on Bylot Island (Sirmilik National Park, Canada). Photo: Ansgar Walk.

Rogen moraines

Rogen moraines are named after a lake in Sweden where the moraine pattern is particularly clear. Rogen moraines create perpendicular depressions in relation to the glacier that often fill up with water, creating lakes and a distinctive striped look.

The forested ridges in Lake Rogen, Sweden are Rogen moraines.  Photo: Wenkbrauwalbatros.

The forested ridges in Lake Rogen, Sweden are Rogen moraines. Photo: Wenkbrauwalbatros.

Terminal or end moraines

Terminal, or end moraines, are left by the end of a glacier. The materials that make up the moraine are shifted from the top of the glacier to the bottom as it moves and flows. The end result of the moraine (its shape and size) are directly correlated to how fast the glacier is moving or melting and what kind of landscape it is moving through. The slower a glacier moves the bigger the moraine will be as the glacier has more time to accumulate outside debris.

Terminal moraine of a small glacier on Baffin Island, Nunavut, Canada. Sometimes known as an end moraine, a terminal moraine is an accumulation of soil and rock that shows the farthest point of a glacier's advance. Credit: NASA / Michael Studinger

Terminal moraine of a small glacier on Baffin Island, Nunavut, Canada. Sometimes known as an end moraine, a terminal moraine is an accumulation of soil and rock that shows the farthest point of a glacier’s advance. Credit: NASA / Michael Studinger

Recessional moraines

This kind of moraine runs across the landscape behind a terminal moraine. They are caused by times when the glacier slows or stops in its movement and can be used to research the glacier further.

September 2002 northeast-looking oblique aerial photograph of a > 100-foot-high moraine formed by a retreating unnamed glacier, Harris Peninsula, Kenai Fjords National Park, Kenai Mountains, Alaska.  Source: USGS.

September 2002 northeast-looking oblique aerial photograph of a > 100-foot-high moraine formed by a retreating unnamed glacier, Harris Peninsula, Kenai Fjords National Park, Kenai Mountains, Alaska. Source: USGS.

Medial moraines

Medial moraines are ridges of debris that are left down a valley floor at the intersection of two glaciers. Both glaciers merge together and their debris combine to form a consistent moraine field along their borders.


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Medial Moraines of Barnard Glacier, Wrangell-St. Elias National Park & Preserve.  Photo: National Park Service.

Medial Moraines of Barnard Glacier, Wrangell-St. Elias National Park & Preserve. Photo: National Park Service.

Supraglacial moraines

Supraglacial moraines come from debris that gathers on the surface of a glacier due to melting surface ice, movement on the upper layers of the glacier, and falling debris from valley walls.

Washboard moraines

Washboard moraines are small, ridged debris field that look just like their name- washboards! They can be spread out over large areas or small depending on the size of the glacier and landscape around them.

Veiki moraines

Veiki moraines are found in parts of Sweden and Canada and are characterized by elevations and depressions. The depressions are usually filled with water creating an island/pond look.

Reference

National Snow and Ice Data Center. 2014. Glacier Landforms: Moraines. Web access 4 January, 2015. http://nsidc.org/cryosphere/glaciers/gallery/moraines.html