In sedimentary geology and geomorphology, the term progradation refers to the growth of a river delta farther out into the sea over time. This occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is greater than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion. As a result, progradation is most common:
- during periods of sea-level fall which results in marine regression. This can occur during major continental glaciations within ice ages, periods during which mass anomalies cause the local geoid to rise, and due to an overall deepening of ocean basins that can often be caused by the presence of older, deeper sea floor.
- with extremely high sediment input, such as in the Yellow River in China, which drains the Loess plateau.
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