Patience with sandpaper
How Do Rivers Carve Canyons?
Water carries grit, grit grinds rock, and enough time turns a stream into a canyon.
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Step 1 of 5
Water on its own barely scratches rock.
Pure water flowing over hard rock does very little. What matters is what the water is carrying.
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Step 2 of 5
Moving water carries sand and stones.
Faster flow lifts bigger particles. A calm stream carries silt; a flood can roll boulders. The load is the cutting tool.
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Step 3 of 5
Every grain takes a tiny bite.
Each particle striking the bed chips off something microscopic. A single grain is nothing. Trillions of them, every second, for ages, is a canyon.
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Step 4 of 5
Cutting down is only half of it.
A canyon is two processes: one going down, one falling in. Rivers also undercut their banks, which collapse and widen the valley. A canyon gets deep from the river and wide from the sides falling in.
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Step 5 of 5
Time is the ingredient that shocks people.
The Colorado River deepens the Grand Canyon by roughly the thickness of a sheet of paper each year. It has been doing it for six million years.
Erosion also builds: everything carried away is dropped somewhere else, forming deltas and beaches.
The short version
Rivers cut canyons by grinding with the sand they carry, and by undercutting banks — given enough time.
Try it yourself
Run water over a tray of sand, then add gravel to the water. The gravel-laden flow cuts a channel far faster.