Mouth bar
Encyclopedia
A mouth bar is a bar
in a river
that is typically created in the middle of a channel
in a river delta
. It is created by a positive feedback
between mid-channel deposition
and flow divergence. As the flow diverges near the ocean
, sediment
settles out in the channel and creates an incipient mouth bar. As flow is routed around the incipient bar, additional sediment is deposited on the incipient bar. This continued process results in the formation of a full-fledged mouth bar, which causes the channel to bifurcate
. This continued process leads to the characteristic fractal tree pattern found in some prograding
river-dominated deltas.
Bar (river morphology)
A bar in a river is an elevated region of sediment that has been deposited by the flow. Types of bars include mid-channel bars , point bars , and mouth bars...
in a river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
that is typically created in the middle of a channel
Channel (geography)
In physical geography, a channel is the physical confine of a river, slough or ocean strait consisting of a bed and banks.A channel is also the natural or human-made deeper course through a reef, sand bar, bay, or any shallow body of water...
in a river delta
River delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...
. It is created by a positive feedback
Positive feedback
Positive feedback is a process in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system that responds to a perturbation in a way that reduces its effect is...
between mid-channel deposition
Deposition (geology)
Deposition is the geological process by which material is added to a landform or land mass. Fluids such as wind and water, as well as sediment flowing via gravity, transport previously eroded sediment, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of...
and flow divergence. As the flow diverges near the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
, sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
settles out in the channel and creates an incipient mouth bar. As flow is routed around the incipient bar, additional sediment is deposited on the incipient bar. This continued process results in the formation of a full-fledged mouth bar, which causes the channel to bifurcate
River bifurcation
River bifurcation occurs when a river flowing in a single stream separates into two or more separate streams which continue downstream. Some rivers form complex networks of distributaries, especially in their deltas...
. This continued process leads to the characteristic fractal tree pattern found in some prograding
Progradation
In sedimentary geology and geomorphology, the term progradation refers to the growth of a river delta farther out into the sea over time. This occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is greater than the volume of the delta that is lost...
river-dominated deltas.