Aggradation

Aggradation

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Aggradation in geology is the accumulation of sediment in rivers and nearby landforms. Aggradation occurs when sediment supply exceeds the ability of a river to transport the sediment. As an example, the quantity of sediment entering a river channel may increase when climate becomes drier. The increase in sediment is caused by a decrease in soil binding that results from plant growth being suppressed. The drier conditions cause river flow to decrease at the same time as sediment is being supplied in greater quantities. Hence, the river becomes choked with sediment.

The river is flowing on bedrock in the upper image, but because sediment was deposited over time the riverbed has risen. This has caused the house to be buried in the lower image. A change in climate, land use, or geologic activity may have caused the aggradation. For example, volcanic eruptions may lead to rivers carrying large amounts of sediment that can accumulate in a channel and bury the old channel and floodplain.

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