HOME

TheInfoList



OR:

A slip-off slope is a depositional
landform A landform is a natural or anthropogenic land feature on the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, m ...
that occurs on the inside convex bank of a
meandering river A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank (cut bank) and deposits sediments on an inner, convex bank ...
. The term can refer to two different features: one in a freely meandering river with a
floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...
and the other in an
entrenched river An entrenched river, or entrenched stream is a river or stream that flows in a narrow trench or valley cut into a plain or relatively level upland. Because of lateral erosion streams flowing over gentle slopes over a time develops meandering (sn ...
.


Freely meandering rivers

In a freely meandering river, a ''slip-off slope'' is characterized by a gentle slope composed of
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
and
pebble A pebble is a clast of rock with a particle size of based on the Udden-Wentworth scale of sedimentology. Pebbles are generally considered larger than granules ( in diameter) and smaller than cobbles ( in diameter). A rock made predominant ...
s on the inside convex bank of a meander loop, across the channel from a
cut bank A cut bank, also known as a river cliff or river-cut cliff, is the outside bank of a curve or meander in a water channel (stream), which is continually undergoing erosion.Essentials of Geology, 3rd Ed, Stephen Marshak Cut banks are found in abu ...
or river-cut cliff.Scheffers, A.M., May, S.M. and Kelletat, D.H., 2015. ''Forms by Flowing Water (Fluvial Features).'' In ''Landforms of the World with Google Earth.'' (pp. 183-244). Springer, Amsterdam, Netherlands. 391 pp. As water in a meandering river travels around a bend, it moves in a secondary corkscrew-like flow as it travels downstream, in a pattern called
helicoidal flow Helicoidal flow is the cork-screw-like flow of water in a meander. It is one example of a secondary flow. Helicoidal flow is a contributing factor to the formation of slip-off slopes and river cliffs in a meandering section of the river. Th ...
. This phenomenon causes increased water velocity in the outside bend of the meander, driving lateral
bank erosion Bank erosion is the wearing away of the banks of a stream or river. This is distinguished from erosion of the bed of the watercourse, which is referred to as ''scour''. The roots of trees growing by a stream are undercut by such erosion. As the ...
. It is also responsible for slower water velocity on the inner bend of the meander. This low velocity allows eroded
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand a ...
s from the cut bank side to be deposited on the inner bank. The deposition of material at the toe of a slip-off slope often results in the formation of a
point bar A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on ...
. Geologically, the environment in which a slip-off slope is deposited is considered to be one of low energy. This continual process of erosion of the outer bank and deposition on the inside bank causes the migration of meanders and formation of
oxbow lake An oxbow lake is a U-shaped lake or pool that forms when a wide meander of a river is cut off, creating a free-standing body of water. In South Texas, oxbows left by the Rio Grande are called '' resacas''. In Australia, oxbow lakes are call ...
s as the meander necks are narrowed and eventually cut through by the river. Because they are low-lying, slip-off slopes are easily inundated during high water events, contributing to floodplain evolution in the middle and lower courses of a river.


Entrenched rivers

The ''slip-off slope'' of an entrenched meander is a gently sloping bedrock surface that rises from the inside, concave bank of an asymmetrically entrenched river. A thin, discontinuous layer of alluvium often covers this gently sloping bedrock surface. This type of slip-off slope is formed by the contemporaneous migration of a meander as a river cuts downward into bedrock.Davis, W.M., 1913. ''Meandering valleys and underfit rivers.'' ''Annals of the Association of American Geographers'', 3(1), pp. 3-28.Crickmay, C.H., 1960. ''Lateral activity in a river of northwestern Canada.'' ''The Journal of Geology'', 68(4), pp. 377-391. A terrace on the slip-off slope of a meander spur, known as slip-off slope terrace, can be formed by a brief halt during the irregular incision by an actively meandering river.Herrmann, H. and Bucksch, H., 2014. ''Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik: English-German/Englisch-Deutsch.'' Springer, Berlin, Germany. 1549 pp.


See also

*
Deposition (geology) 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 ...
*
Meander cutoff A meander cutoff is a natural form of a cutting or cut in a river occurs when a pronounced meander (hook) in a river is breached by a flow that connects the two closest parts of the hook to form a new channel, a full loop. The steeper drop in grad ...


References

{{river morphology Geomorphology Fluvial landforms Limnology de:Gleithang