Meanders: Rivers That Cannot Hold a Straight Line

A river on flat ground rarely stays straight for long. Where the channel curves, water on the outside of the bend moves faster and cuts into the bank, while the slower water on the inside drops sand and silt. Over years the outer bank retreats and the inner one grows, so every bend gradually becomes a deeper bend. Geomorphologists put the length of one full meander at roughly ten to fourteen times the channel's width, a ratio that holds surprisingly well from small streams to large rivers.

Aerial photographs make the process legible because the inside of each bend is usually pale: point bars of fresh sand, sometimes crossed by curved lines of young willows that mark older water edges, one inside the next. The outer bank is darker and steeper, often undercut, with trees leaning out over it. Where two bends grow towards each other, a flood eventually cuts across the narrow neck and the river abandons the loop, which stays behind as a crescent-shaped oxbow lake and slowly fills with reeds.

From a plane window the whole pattern looks deliberate, like a line drawn by a hand that kept changing its mind. On a screen it holds attention for a related reason: one strong curving line crossing a quiet field of green or brown, with no horizon to anchor it and no obvious up or down. The eye follows the water from one edge of the display to the other, and then, without quite deciding to, starts again.