Why do Some Rivers have Deltas?

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A river delta is caused by deposits at the mouth of a river. When a river flows across a flat plain into the sea, it flows very slowly. The river water cannot hold so much of silt that it has carried with it and so it deposits soil and sand on the plain. In time, this sediment begins to form mudbanks. The river water flows through these sediments in many channels, often changing direction. This wide, blocked-up mouth with many channels is called a delta. This is because its shape is often like the Greek letter delta.

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