Glacial processes

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Glaciers move downhill under their own weight:

  • meltwater underneath a glacier allows the glacier to slide over the ground (basal sliding) and this is the main way warm-based glaciers move
  • there's more melting around bits of rock protruding from the valley floor, because there's more pressure on the ice (so the ic melts at temperatures lower than 0). Meltwater can refreze downstream of the obstruction where there's less pressure, so the flow tends to be faster around the obstruction, and slower downstream
  • glaciers move in an arc shape when they're in a hollow (by basal sliding). This is called rotational flow
  • Internal deformation is where the ice bends and warps to flow downhill like a liquid. It's caused by ice crystals shifting past each other and is the main way cold-based glaciers move
  • at the head of a glacier the valley is steep, so there's a strong gravitational force pulling the ice downwards - making the ice move quickly. When ice moves quickly there's more tension (pulling apart), which causes the ice to fracture into thick layers. The layers then slip downwards - this is called extentional flow
  • Lower down the glacier the ic is moving more slowly because the valley is less steep. the faster ice from the head of the glacier pushes down on the slower ice and compresses it. The high pressure causes the ice to fracture into layers, and the layers slip forwards - this is called compressional flow

The main things that determine the speed at which a glacier flows are the gradient of the valley floor and the thickness of the ice and the temperature at the base of the glacier.

The steeper the valley, the faster the glacier will flow. The thicker the ice, the faster it will flow - in a warm-based glacier thicker ice exerts more pressure on the valley floor, causing more melting which makes it flow faster. In cold-based glaciers thicker ice means there's more internal deformation, whicch makes it flow faster. The warmer the base the faster it will flow.

Ice moves near the glacier's surface than…

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