DEFINITION OF MORAINE

A landform made of unstratified, unsorted glacial

drift, produced by dumping, lodging, or pushing by a glacier.

It has a constructional topography that is independent of the

surface that it rests on. There are many different types of

moraines, produced in a variety of ways by direct action of

glacial ice. An advancing or stationary glacier may have hundreds

of meters of glacial till wedged in front of it, and this

till will fall, making an elongate terminal moraine when the

glacier begins to retreat. As a glacier retreats, it may leave a

rather level gravel plain, outwash plain, or ground moraine if

the retreat is water-rich. Recessional moraines are similar to

terminal moraines, except that they mark places where the

glacier temporarily paused during its retreat. Knob and kettle

or hummocky topography is produced during jerky, onagain,

off-again styles of glacial retreat, where many large

blocks of ice may get left behind, forming large depressions

known as kettle holes in the outwash plain as the glacier

retreats. These typically become filled by water to form kettle

lakes after the retreat.

There are many types of moraines formed in glaciated

terranes that may or may not be experiencing retreat. Lateral

moraines form on the sides of mountain and valley glaciers in

response to plucking of material off the mountainsides by the

ice as it passes, and by material that avalanches off from

oversteepened slopes. Medial moraines form where two

glaciers join together, and their lateral moraines merge in the

center of the new larger glacier.

Glacial moraines form extensive deposits of gravel that

are easily mined, since they rest on the surface. A wide variety

of grain sizes of gravel and sand may be found in an individual

moraine, with steeper surface slopes reflecting coarsegrained

material, since larger grains and clasts have a steeper

angle of repose than finer grains.

See also GLACIER.

mountain breeze See KATABATIC WINDS.

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