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USGS CMG InfoBank: Deltas

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Comment: 10:05 - 11:08 (01:03)
Source: Annenberg/CPB Resources - Earth Revealed - 20. Running Water II: Landscape Evolution
Keywords: "Dee Trent", valley, river, landscape, landform, stream, ocean, lake, "flow velocity", deposition, delta, slope, gradient, sediment, deposition, distributary, "river channel"

Our transcription: River valleys form a significant part of Earth's landscape, but they are not the only landform created by running water.
All streams and rivers come to an end.
Most ultimately flow into the ocean or another large body of water such as a lake.
Due to the sudden loss in velocity at the mouth of a river, most of its sediment is deposited forming a "delta."
Deltas, of course, form at the mouth of the river where they enter a large lake or the ocean.
The gradient or the slope of the river is very gentle.
When it hits the water there is no gradient; consequently, the sediment begins to settle out immediately.
In so doing, it dams its channel, and the river tends to branch into a series of "distributaries."
From time to time the certain branches load up with more sediment than others, so the main flow of the river may shift from one locality to another over a long period of time.

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