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Three-dimensional
diagram illustrating a river meander with a point
bar being formed on one bank and erosion occurring
on the other bank
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Point bars are formed at bends in rivers and can be composed
of gravel, sand, silt and clay. Their characteristic half-ellipse
shape is easily recognizable. Because of the way they
are formed, point bars occurring in modern rivers have
the same shape as point bars that were formed in rivers
millions of years ago.
Point bars get their unique shapes because of the way
water flows through curving channels like bends in a river.
As the water enters the bend of the river the flow spins
in a spiral. The flow is strongest on the outside of the
bend causing erosion of the outer bank. As the water flows
away from the outer bank and rises up the slope of the
inner bank, or point bar, it loses some of its energy
and begins to deposit sediments eroded from the outer
bank. First the coarse grains are deposited near the base
of the point bar and then the finer grains as the water
flows towards the top of the point bar.
The processes that deposit point bars are the same in
large and small rivers. As a result, all point bars also
have the same kind of shape whether they are large or
small.Scientists use this knowledge to help them make
computer models of underground formations.
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