Formations

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  • Created by: Isla S
  • Created on: 12-05-14 08:34

Delta

  • Feature of deposition formed when a river flows into a standing body of water (at coast, river entering the sea)
  • Deposition occurs as the velocity drops upon entering the standing body of water which reduces the capacity and competence of the river - bedload and suspended material are dumped
  • Flocculation occurs - fresh water mixes with salt water - tiny particles in suspension (clay, silt) coagulate with the salt in the water and become heavy enough to sink - deposited.
  • Deltas only form where rate of deposition exceeds the rate of sediment removal
  • Composed of three types of deposit
  • Topset beds: Larger and heavier particles are first to be deposited
  • Foreset beds: Medium calibre particles travel a little further before desposited
  • Bottomset beds: Finest particles travel far before low velocity/flocculation leads to their deposition
  • 3 main shapes - Arcuate, Birds Foot and Cuspate
  • Arcuate most common - The Nile delta
  • Birds Foot - Mississippi delta
  • Cuspate - river Ebro delta in Spain
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Pingo

Open system Pingo

  • Mound of earth covered ice found in the arctic and subarctic
  • Where permafrost is discontinuous or thin, freezing water in the upper layer of the soil leads to expansion of ice within the soil
  • Overlying sediment on the ground heaved upwards - dome shaped feature (pingo - less than 50m in height)

Closed system Pingo

  • Where there is continuous permafrost on low land areas
  • Accumulate where there is a small lake  that has been drained and groundwater is trapped due to freezing from above and permaforst beneath
  • Trapped water expands due to hyrdostatic pressure turning it to ice - pushes material and sediment upwards to form a conical shaped mound - pingo.
  • If centre collapses, it can fill with water - small lake
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Ice Wedge

  • When temp in winter are so cold - crack in the ground surface - metre deep and a few mm wide
  • When it gets warmer, active layer melts and what was once snow releases water - in cracks. 
  • Water freezes when it touches the permafrost, and expands the size of the crack
  • Long period of time - repeat its self - cracks expanding - ice wedge
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