Fluvioglacial processes

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  • Created by: Tom
  • Created on: 09-05-13 17:46

meltwater stream

  • when glacial ice melts, water runs out and forms streams of melt water. warm-based glaciers and retreating glaciers produce lots of melt water
  • surface meltwater filters throguuh the glacier (e.g. runnign through crevasses) and flows through tunnels underneath the glacier, before running out of the snout of the glacier
  • melt water streams cause erosion in the same way as normal rivers - but they cause more erosion than rivers of the same size. this is because the pressure of the ice means that melt water streams flow very quickly - so they can carry lots of material that erodes the landscape.
  • melt water streams form deep troughs in the landscape called melt water channels. because melt water streams have a lot of erosive power, the melt water channels they produce are very wide and deep. after the glacier has retreated, the deep melt water channels are left with very shallow streams running through them.
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fluvioglacial deposits

  • glacial melt water carries a large load of sediment of various sizes (from inside, on top of and underneath the glacier)
  • melt water streams deposit their load on the valley floor as they flow away from the glacier
  • melt water streams are ofter braided - they split into lots of mini streams that cross over each other. this is because when the melt water is flowing more slowly (e.g. in winter, when the amount of melt water is lower) it cant carry its load - so it deposits the sediment on the ground, and splits into two streams to get round it.
  • threes a difference between glacial deposition features formed by glaciers dropping debris as they melt and fluvioglacial depositional features formed by melt water carrying debris, then depositing it away from the glacier
  • fluvioglacial deposits are sorted - the fine sediment is seporated from the larger sand which is seperated from the gravel and so on. glacial deposits are unsorted.
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outwash plains

  • an out wash plain is a layer of gravel, sand and clay that forms in front of where the snout of the melting glacier used to be. melt water flows out of the glacier, and carries the sediment with it
  • sediments on outwash plains are sorted into layers. gravel gets dropped first because its heavier than sand and clay, so it forms the bottom layer of the out wash plain. clay is dropped last and gets carried furthest away from the snout because its the lightest sediment - it forms the top layer of the out wash plain
  • blocks of ice that have broken off from the front of the glacier can get surrounded and partly buried by the fluvioglacial deposits. when the blocks of ice melt, they leave holes in the outwash plain called kettle holes.
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eskers

  • eskers are long, winding ridges of sand and gravel that run in the same direction as the glacier. they're deposited by melt water streams flowing in tunnels underneath the glacier - when the glacier retreats and the stream dries up, the load remains as an esker. eskers show you where the glacial tunnel used to be.

(http://www.sup.org.uk/images/bedshiel_esker.jpg)

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Kames

  • kames are mounds of sand and gravel found on the valley floor. melt water streams on top of glaciers collect in depressions and deposit layers of debris. when the ice melts the debris is dumped onto the valley floor.
  • kame terraces are piles of deposits left against the valley wall by melt water streams that run between the glacier and valley sides. they look like lateral moraine but there sorted into layers - melt water streams deposit their heaviest load first, so kame terraces have gravel at the bottom and sand on top.
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proglacial lakes

  • lakes can form in front of glaciers e.g. when the flow from melt water streams get dammed by the terminal moraine. as melt water streams flow into a pro-glacial lake, they slow down and deposit their sediment on the ice - these deposits are known as deltas. when ice melts, these deltas are dumped on the valley floor, forming delta kames

(http://academic.emporia.edu/aberjame/ice/lec07/f7h2.jpg)

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