Meander
A
meander is a bend in a river, also known as an
oxbow loop. A stream or river flowing through a wide valley or flat plain will tend to form a
meandering stream course as it alternatively erodes and deposits
sediments along its course. The result is a
snaking pattern as the stream meanders back and forth across its
floodplain. When a meander gets cut off from the main stream body, an
oxbow lake is formed.
A meander is formed because the river flows faster on the outside edge of any small curve and slower along the inside edge.
Deposition of
sediment occurs on the inner edge because the river, moving slowly, cannot carry its sediment load, creating a slip-off slope. The faster moving current on the outside bend has more erosive ability and the meander tends to grow in the direction of the outside bend, forming a river cliff. This can be seen in areas where
willows grow on the banks of rivers; on the inside of meanders, willows are often far from the bank, whilst on the outside of the bend, the roots of the willows are often exposed and undercut, eventually leading the trees to fall into the river. This demonstrates the river's movement.
If the region later undergoes tectonic uplift, the meandering stream will again resume downward erosion. The meandering pattern will remain as a deep valley known as an
incised meander. Rivers in the
Colorado Plateau and streams in the
Ozark Plateau are noted for these incised meanders.
Sometimes an incised, also known as entrenched, meander is cut off. When it is, the resulting landform is called a rincon. They are created when a river erodes through the narrow neck of land between the ends of a loop, leaving the loop without an active cutting stream. One dramatic rincon on
Lake Powell is called "The Rincon."
The term derives from the
Maeander River river in Turkey, characterised by a very convoluted path. As such, early usage of the term, from the late 1500s, referred to convoluted and windy speech and ideas, as well as the
geomorphological feature. The river in Turkey is called Menderes River, south of Izmir, near the ancient Greek town of Miletos.
Meander ratio is a means of quantifying how much a
river or
stream meanders (how much its course deviates from the shortest possible path). It is calculated as the
length of the stream divided by the length of the
valley. A perfectly straight river would have a meander ratio of 1 (it would be the same length as its valley), while the higher this
ratio is above 1, the more the river meanders.
Lewis C. Shaw,
Pennsylvania Gazetteer of Streams Part II, Commonwealth of Pennsylvania, Department of Environmental Resources, Bulletin No. 16, 1984, page 8.Luna B. Leopold & W.B. Langbein,
River Meanders, Scientific American, June 1966, page 60
