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Geography · entry 50 of 52
Rivers rarely run straight, because erosion constantly bends their channels into curves.
The longer version
Flowing water erodes the outer bank of a bend while depositing sediment on the inner one, so a slight curve grows larger over time. The fastest current runs just outside the centre of the channel, wearing away that side and carrying material downstream. Small irregularities in the bed are enough to start the process.
Eventually a loop can be cut off, leaving a curved lake behind. Bends also lengthen the path, which reduces the gradient and slows the flow. Straight channels occur mainly where the course is controlled by rock, by artificial banks, or by a steep drop that keeps the water fast. Floodplains record old courses as scars.
Where this entry sits
These facts wander across maps, borders, deserts, rivers, mountains, and the extreme corners of the natural world. Each one is short and self-contained, offering a small surprise about places you may never visit rather than anything you actually need. The full list sits on the Geography page, where every entry is listed in order.
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