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every landform in the chapter is one river at a different age.

drag the droplet from Himalayan gorge to delta — one river, four ages

A river spends the same energy differently depending on how far downhill it has already fallen. Near the source the slope is steep, so nearly all the energy goes into cutting straight down — a narrow V-shaped gorge. By the middle course the slope has eased, so the river swings side to side instead, carving sideways until a loop occasionally pinches itself off into an oxbow lake. By the time it reaches the sea there is almost no slope left to cut with, so it drops what it is carrying and splits into a delta. Every landform in between is the same river, just older.

Concepts: erosion, geology.

An interactive you play with one thumb, on Wundr.