How Canyons Form: Water, Ice, and Time

Most canyons form by river erosion over millions of years. The Grand Canyon took 5-6 million years. Slot canyons form from flash floods in soft sandstone.

Glacial valleys are U-shaped while river canyons are V-shaped. Tectonic uplift creates the relief that rivers then carve. Some canyons like Eldgja in Iceland are volcanic fissures..