Why do river deltas form where rivers meet the sea?
Quick Answer
Deltas form when a river slows down and drops the sediment it carries faster than waves and tides can remove it. The deposited material builds new land outward into the water.
The Full Story
As a river reaches a lake, sea, or slow-moving basin, its velocity drops and it can no longer carry as much sediment. Sand, silt, and clay settle out, and the river splits into distributary channels as new deposits block the main flow. Deltas grow where sediment supply is high and coastal currents are weak enough to let accumulation win. Famous examples include the Nile Delta, the Mississippi Delta, and the Ganges-Brahmaputra Delta.
Key Facts
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"A delta is a river building new land grain by grain."
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