Crevasse splay
Encyclopedia
A crevasse splay is a sedimentary fluvial deposit which forms when a stream breaks its natural or artificial levees and deposits sediment on a floodplain
. This breach can cause large deposits that spread in a pattern similar to that of an alluvial fan deposit
. Once the levee has been breached the water flows out of its channel. The larger sediments are deposited first and as the water loses energy the smaller grains fall out of suspension. This can create graded deposits
similar to those found Bouma sequences
. In some cases crevasse splays can cause a river to abandon its old river channel, a process known as Avulsion
. Crevasse splay deposits occur most commonly on the outside banks of meanders
where the water has the highest energy. The deposits can range in size. Larger splays can be 6 meters thick at the levee and spread 2 kilometers wide. While smaller splays may only be centimeters thick.
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
. This breach can cause large deposits that spread in a pattern similar to that of an alluvial fan deposit
Alluvial fan
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial...
. Once the levee has been breached the water flows out of its channel. The larger sediments are deposited first and as the water loses energy the smaller grains fall out of suspension. This can create graded deposits
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
similar to those found Bouma sequences
Bouma sequence
right|300px|thumbnail|Complete Bouma sequence in Devonian Sandstone The Bouma Sequence describes a classic set of sedimentary beds deposited by a sediment-water turbidity current...
. In some cases crevasse splays can cause a river to abandon its old river channel, a process known as Avulsion
Avulsion (river)
In sedimentary geology and fluvial geomorphology, avulsion is 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.-Deltaic and...
. Crevasse splay deposits occur most commonly on the outside banks of meanders
Meander
A meander in general is a bend in a sinuous watercourse. A meander is formed when the moving water in a stream erodes the outer banks and widens its valley. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the...
where the water has the highest energy. The deposits can range in size. Larger splays can be 6 meters thick at the levee and spread 2 kilometers wide. While smaller splays may only be centimeters thick.
See also
- Fluvial landforms
- MeanderMeanderA meander in general is a bend in a sinuous watercourse. A meander is formed when the moving water in a stream erodes the outer banks and widens its valley. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the...
- AvulsionAvulsion (river)In sedimentary geology and fluvial geomorphology, avulsion is 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.-Deltaic and...
