moraine

moraine (mərān`), a formation composed of unsorted and unbedded rock and soil debris called till, which was deposited by a glacier. The till that falls on the sides of a valley glacier from the bounding cliffs makes up lateral moraines, running parallel to the valley sides. When two or more valley glaciers unite, their lateral moraines form a medial moraine, running down the center of the glacier. When two or more lobes of a continental ice sheet unite, the debris carried by each lobe intermingles, forming an interlobate moraine. When the climate of a region becomes warmer, glaciers will start receding. The debris deposited by a melting glacier is called a ground moraine. The debris left at the edge of the glacier's extreme forward movement is a terminal moraine. Similar moraines deposited during a temporary halt in the retreat of glacial ice are called recessional moraines. After the retreat of a glacier the moraines remain as prominent features of the topography. The margins of the great ice sheets of the Pleistocene epoch are marked by terminal moraines stretching across North America and Europe. See drift.

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moraine

Medial moraine of Gornergletscher (Gorner Glacier) in the Pennine Alps near Zermatt, Switz.

(credit: Jerome Wyckoff)

Accumulation of rock debris (till) carried or deposited by a glacier. The material may range in size from blocks or boulders to sand and clay, is unstratified when dropped by the glacier, and shows no sorting or bedding. Several kinds of moraines are recognized, depending on how they are deposited by the glacier; these include lateral moraines along the margins of the glacier and terminal moraines at its leading edge.