River Delta

geography · rivers · landforms · sediment

Triangle Shape. River deltas are named after the Greek letter delta (Δ) because they look like a triangle when you see them from above. The river splits into smaller branches as it spreads out its load of sediment.

Where Rivers Meet Water. Deltas form at the mouth of a river, where it flows into an ocean, sea, lake, or even another river. The flowing water slows down and can no longer carry all its sediment, so it drops the sand, mud, and silt to build new land.

Built by Sediment. Rivers constantly carry tiny pieces of rock and soil from upstream, and when the water slows at a delta, all that material settles down and stacks up. Over thousands of years, these deposits create brand new land that grows outward into the water.

Balance of Forces. Whether a delta grows or shrinks depends on how much sediment the river brings versus how much the ocean waves and currents wash away. A river supplying lots of sediment will build a bigger delta than one with less material to deposit.

Home to Many Species. Deltas are incredibly rich habitats where freshwater mixes with saltwater, creating unique environments for fish, birds, and plants that nowhere else can match.