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A delta forms where a river meets a lake. [10] River deltas form when a river carrying sediment reaches a body of water, such as a lake, ocean, or a reservoir. When the flow enters the standing water, it is no longer confined to its channel and expands in width.
Deposition is the geological process in which sediments, soil and rocks are added to a landform or landmass. Wind, ice, water, and gravity transport previously weathered surface material, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of sediment.
When the glacier meets the ocean and begins to break apart or melt, these particles get deposited. Most of the deposition will happen close to where the glacier meets the water, but a small amount of material is also transported longer distances by rafting, where larger pieces of ice drift far from the glacier before releasing their sediment. [1]
Avulsions are common in river deltas, where sediment deposits as the river enters the ocean and channel gradients are typically very small. [2] This process is also known as delta switching. Deposition from the river results in the formation of an individual deltaic lobe that pushes out into the sea.
Drowned river valleys are also known as coastal plain estuaries. In places where the sea level is rising relative to the land, sea water progressively penetrates into river valleys and the topography of the estuary remains similar to that of a river valley. This is the most common type of estuary in temperate climates.
The faster the water in a river channel, the better it is able to pick up greater amounts of sediment, and larger pieces of sediment, which increases the river's bed load. [4] Over a long enough period of time, the combination of deposition along point bars, and erosion along cut banks can lead to the formation of an oxbow lake .
A river mouth is where a river flows into a larger body of water, such as another river, a lake/reservoir, a bay/gulf, a sea, or an ocean. [1] At the river mouth, sediments are often deposited due to the slowing of the current, reducing the carrying capacity of the water. [ 1 ]
Spits occur when longshore drift reaches a section of headland where the turn is greater than 30 degrees. The spit will continue out into the sea until water pressure (e.g. from a river) becomes too great to allow the sand to deposit. Vegetation may then start to grow on the spit, and the spit may become stable and often fertile.