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Glacier Deposition and Moraines

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The awesome force of a glacier or ice sheet can carve impressive valleys, such as Yosemite Valley, and can bulldoze wide swaths of continents. The rock and soil picked up and transported by glaciers creates new landscapes as it is eventually deposited by melting and retreating glaciers.

"Drift" is the generic term for all glacially deposited material. The term is derived from the old theory that rock and soil deposits around the world were not produced by glaciers or ice sheets, but were deposited by the Great Flood of biblical fame.

Here's a short glossary of different types of glacial and ice sheet depositions:

  • Glacial flour - rock ground to the texture of a fine powder. It usually flows out of a glacier as sediment in a glacial meltwater stream running from the glacier.
  • Till - refers to an unconsolidated and unsorted mixture of sediment, clay, gravel, and rocks deposited by a glacier.
  • Moraine - a French word that refers to any glacier-formed accumulation - there are a variety of moraines.
  • Terminal moraine - an accumulation at the outermost edge of where a glacier or ice sheet existed.
  • Recessional moraine - moraine located "behind" the outermost edge of a glacier, formed when the glacier lingers in one spot for a long time.
  • Ground moraine - gently rolling hills and plains deposited by ice.
  • Lateral moraine - ridges of till on the sides of a glacier.
  • Medial moraine - a moraine formed when two glaciers merge (a tributary and trunk glacier) and their lateral moraines come together to form a single moraine.
  • Push moraine - a moraine created by till that was a moraine deposited by an earlier glacier that once covered the area.
  • Ablation moraine - a moraine formed from material that fell upon the glacier.
  • Glacial erratics - large boulders that had been carried by the ice and deposited. They are much different in size than surrounding till.

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