Einstein once lectured on why rivers wiggle, and a Turkish river named the loops
The word meander comes from a Turkish river so twisting that ancient Greeks used its name for anything winding. In 1926 Albert Einstein proposed that Earth's rotation might start the bends. The real engine is subtler: a corkscrew current that digs out one bank and piles sand on the other.
The river is the Menderes, known to the Greeks as Maiandros, flowing south of Izmir past ancient Miletus. By Classical times its name had become an everyday word for convoluted patterns, speech and ideas. The geographer Strabo remarked that its course was so tortuous that everything winding was named after it.
In a bend, water does not simply follow the curve. Near the stream bed, friction slows the flow almost to a stop, so outward centrifugal force vanishes there while the inward pressure of water piled against the outer bank remains. Bottom water therefore creeps toward the inside of the bend, and surface water flows back outward, producing a helical, corkscrew motion similar to the one that gathers tea leaves in the centre of a stirred cup. The faster flow on the outer bank erodes it into a cut bank, while slower water on the inside drops sediment to form a point bar. Because deposition keeps pace with erosion, the channel's width stays roughly constant as the whole loop migrates.
The process feeds on itself. As the geologist Elizabeth Wood put it, more curvature brings more bank erosion, which brings more curvature, until a loop is cut off. Einstein told the Prussian Academy of Sciences that the Coriolis effect could tilt velocity toward one bank and kick-start the process, but that force is now thought too weak to matter much. Other explanations stress random obstacles steering flow, or a river lengthening its path until the energy it spends matches the sediment it can carry.
Meanders obey surprisingly regular proportions. A river counts as meandering when its channel is at least 1.5 times longer than the straight valley distance. One full meander typically spans 10 to 14 channel widths, and the belt the river wanders across is usually 15 to 18 channel widths wide, which is why migrating bends can threaten roads and bridges.
Source: Meander
