1001 Space Earth Earth Rocks and Minerals Landscape Sea Weather and Climate Natural Disasters Resources Nature History Human World Science and Technology

Choose a Page:What is the rock cycle?What is weathering?What shapes the cliffs along the s...Do rocks dissolve?Can living things break down rocks?How are caves made?How do sand dunes move?Why do desert rocks have fantastic...How do rivers form?*What makes waterfalls?*What is scree?What is an oxbow lake?Is all erosion slow? What makes waterfalls? A fast-flowing river erodes its bed downward. This erosion is not constant, but depends on the hardness of the rock over which the water is passing. When there is a particularly hard bed of rock in the river, it erodes so slowly that the river falls over it as a waterfall. The downstream rocks are eroded into a 'plunge pool'. Eventually the hard rock at the top of the waterfall is undermined and the river can cut back into it as a gorge. The plunging waters of Niagara Falls are gradually undermining the hard dolomite rock and retreating upstream.   Previous: Back Book: 1001 Section: Earth Chapter: Landscape