Avulsion (river): Difference between revisions
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Avulsions usually occur as a downstream to upstream process via head cutting erosion. If a bank of a current stream is breached a new trench will be cut into the existing floodplain. It either cuts through floodplain deposits or reoccupies a old channel. <ref>Nanson, G.C., and Knighton, A.D. 1996. Abranching rivers: Their cause, character, and classification. ''Earth Surface Processes and Landforms'' 21:217-39</ref> |
Avulsions usually occur as a downstream to upstream process via head cutting erosion. If a bank of a current stream is breached a new trench will be cut into the existing floodplain. It either cuts through floodplain deposits or reoccupies a old channel. <ref>Nanson, G.C., and Knighton, A.D. 1996. Abranching rivers: Their cause, character, and classification. ''Earth Surface Processes and Landforms'' 21:217-39</ref> |
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In this link small avulsions can be seen breaking from the main channel in a delta created in a lab at Western Washington University. This is a time lapse image of the delta. [http://mswebtest.admcs.wwu.edu/deltacam/main.aspx] |
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== References == |
== References == |
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{{reflist}} |
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Revision as of 20:55, 1 December 2008
In sedimentary geology and fluvial geomorphology, avulsion refers to the rapid abandonment of a river channel and the formation of a new river channel. Avulsions occur as a result of channel slopes that are much lower than the slope that the river could travel if it took a new course. [1]
Avulsions are common in deltaic settings, where deposition as the river enters the ocean results in infilling of the channels. Sediment is deposited as topset beds, resulting in the rise of the delta to provide the stream sufficient gradient to flow to the water's edge. The main channel in which the deposition is occuring causes repeated splitting of the stream in to distributary channels. This action of main channel splitting into different streams is called an avulsion.[2]
Subsidence of the delta and/or sea-level rise can further cause backwater and deposition in the delta. This deposition fills the channels and leaves a geologic record of channel avulsion in sedimentary basins. On average, an avulsion will occur every time the bed of a river channel aggrades enough that the river channel is superelevated above the floodplain by one channel-depth. In this situation, enough hydraulic head is available that any breach of the natural levees will result in an avulsion. [3] [4]
An example of a minor avulsion is known as a meander cutoff, where the high-sinuosity meander bend is abandoned in favor of the high-slope. Slingerland and Smith show that this occurs when the ratio between the channel slope and the potential slope after an avulsion is less than 1/6.[1]
Avulsion typically occurs during large floods which carry the power necessary to rapidly change the landscape.
Avulsions usually occur as a downstream to upstream process via head cutting erosion. If a bank of a current stream is breached a new trench will be cut into the existing floodplain. It either cuts through floodplain deposits or reoccupies a old channel. [5]
In this link small avulsions can be seen breaking from the main channel in a delta created in a lab at Western Washington University. This is a time lapse image of the delta. [1]
References
- ^ a b Slingerland, R. and N. D. Smith (1998), Necessary conditions for a meandering-river avulsion, Geology (Boulder), 26, 435-438.
- ^ Easterbrook, Don J.Surface Processes and Landforms Second EditionPrentice Hall, New Jersey: 1999.
- ^ Bryant, M., P. Falk, and C. Paola (1995), Experimental study of avulsion frequency and rate of deposition, Geology (Boulder), 23, 365-368.
- ^ Mohrig, D., P. L. Heller, C. Paola, and W. J. Lyons (2000), Interpreting avulsion process from ancient alluvial sequences; Guadalope-Matarranya system (northern Spain) and Wasatch Formation (western Colorado), Geological Society of America Bulletin, 112, 1787-1803.
- ^ Nanson, G.C., and Knighton, A.D. 1996. Abranching rivers: Their cause, character, and classification. Earth Surface Processes and Landforms 21:217-39