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.
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.
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.
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.
I leave you with other interesting loops I’ve found. I’ve left several famous ones out, so you have something left to find.
“Fluvial Features–Meandering Stream.” National Park Service.
“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.