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Understanding modern rock formations has helped scientists to better visualize the shape of formations deep below the surface of the Earth. One such formation is the point bar.

Point Bars

When a river reaches a meander, or a bend in its course, some of the sediments carried by the river are deposited on the inside of the bend. This deposit is called a point bar. Point bars can be composed of gravel, sand, silt, and clay—it all depends on what the river is carrying at that point. All point bars have a characteristic half-ellipse shape that 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.

Three-dimensional diagram illustrating a river meander with a point bar being formed on one bank and erosion occurring on the other bank

Point bars are created where a river or stream curves, or meanders. The faster current on the outside of the curve scours sediment from the river bank, causing a cut back. The sediments are deposited on the inner curve where the water is slower, forming point bars.

Point bars get their unique shape because of the way water flows through the curving channels of bends in a river. As the water enters the river bend, its flow is strongest on the outside of the bend, causing erosion of the outer bank. As the water flows away from the outer bank, it loses some of its energy when it reaches the shallower slope of the inner bank. The sediments eroded from the outer banks are deposited on the inner banks, forming point bars. The coarse sediments are deposited near the base of the point bar, and the finer grains are deposited at the top.

The processes that create point bars are the same in both large and small rivers. As a result, all point bars also have the same kind of shape no matter what size they are. Scientists use this knowledge to help them make computer models of underground formations.

What is the significance of point bars in the search for oil and gas?