The Causes of Meandering Rivers

Image by Alex Hu from Pixabay.

I’m a sucker for sunsets, but what really grabs me about this image is the crazy course of the river. Why does it swing from side to side like that? I did a little research and it turns out that rivers often meander as they approach the end of their run. It’s a somber story this photo tells.

A river emerges from any of several sources–glacier melt (Ganges, Yangtze, Mekong Rivers), a lake (Nile and Mississippi Rivers), other rivers and streams (Amazon and Rio Grande Rivers), an underground spring (Danube and Thames Rivers), or directly from the runoff of rain or snowmelt high in the mountains (Colorado and Potomac Rivers). Whatever the source, the flow of water obeys gravity and rushes toward an ultimate goal of joining the ocean.

Initially, the river courses through steep, v-shaped valleys at considerable speed, increasing in volume on the way down as it’s joined by other streams, creeks, rivers, more rain, even water that escapes the saturated ground through which the river cuts. Eventually, the downward tilt of the valley begins to level out and the valley’s walls to flatten. The river slows and starts to meander from side to side.

A meandering river follows a shallow valley downhill. Image courtesy of Mysid and United States Department of Agriculture at Wiki Commons.

The water courses up one side of the shallow valley until gravity pulls it back around. Inside the great loops of the turning river, rock and other sediment drop out along the inside (convex) banks where the current runs slowest. Meanwhile, the faster flow against the outer (concave) bank causes erosion. This ongoing process of deposition and erosion spreads the meanders further left and right of the valley center.

A meandering river in the Gates of the Arctic National Park and Preserve in Alaska. Photo courtesy of the National Park Service.

At the width of the meanders increases, the loops themselves grow rounder and the neck of land at their base narrows. In many cases, the neck of the loop shrinks until its inner banks touch and finally collapse. The rush of water speeds through, depositing sediment that eventually separates the loop from the course of the river. The isolated body of water is called an “oxbow” lake, so named for the U-shaped harness placed around the necks of cattle.

An oxbow lake off the Connecticut River, as seen from the Landsat 8 satellite in 2017. Photo courtesy of NASA.
Image of the Vltava River in the Czech Republic by Imp5pa from Pixabay. Note the oxbow lake hiding behind that stand of trees on the left.
This satellite image of the Qadisiyah Reservoir on the meandering Euphrates River in Iraq shows the near formation of an oxbow lake. Image from Pexels archive on Pixabay.
Often deposits from meanders form islands, as they have in this Moravian river. Photo by Simy27 from Pixabay.
This meandering river in Vietnam has formed a long finger of land that is now an island. Image by ThuyHaBich from Pixabay.

In photos we’ve seen so far, the sides of the valleys restrict the width of the meanders. When no valley exists, as in a plain close to the coast, the meanders are free to roam haphazardly. At this point in its final rush to the ocean, the meandering river often breaks into many streams to form a “braided” river. A river delta is a form of braided river.

Meander scars cover the broad plain adjacent to the Río Negro River in Argentina. Photo courtesy of NASA on Wiki Commons.
A NASA image of a landscape scarred by a river’s meanders. Note the oxbow lake in blue at the top of the photo.
The delta of Russia’s Lena River, where it joins the Arctic Ocean. Photo from WikiImages on Pixabay.

I leave you with other interesting loops I’ve found. I’ve left several famous ones out, so you have something left to find.

The Schlögener Loop in the Danube River in Austria, where the river has deposited sediment on the inside curve while cutting away soil from the outside curve. Image by haerdirolf from Pixabay.
As it flows through western Germany, the Moselle River has left substantial deposits on an inner curve, upon which sits the town of Pünderich. Photo from Tama66 on Pixabay.

The Green River in Canyonlands National Park. Photo from PublicDomainPictures.
A loop in the meandering Arda River in Bulgaria. Photo by Borislav Krustev from Pexels.
The Melero Meander on Spain’s Alagon River. Image by José Antonio Muñoz from Pixabay.

Works Cited

“Fluvial Features–Meandering Stream.” National Park Service.

“Meander.” Wikipedia.

“Rivers, Streams, and Creeks?” United States Geological Survey.

“River Systems and Fluvial Landforms.” National Park Service.

“Source of the Danube.” Wikipedia.

“Stream and River.” Science Clarified.

“Understanding Rivers.” National Geographic. 14 Mar 2011.

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