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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