Why do waterfalls form in hanging valleys?

Water falls form at very abrupt changes in grade ... this occurs when heavy glacial flow, along a primary deep channel encounters and "cuts off" smaller tributary channels, forming what are known as hanging valleys; Yosemite Falls for example, formed at a typical hanging valley. read more

Hanging Valley. Hanging valleys are often associated with valley glaciers, joining the main valley along its sides. They are the product of different rates of erosion between the main valley and the valleys that enter it along its sides. read more

Tributary valleys with such unequal or discordant junctions are called hanging valleys. In extreme cases where a tributary joins the main valley high up in the steep part of the U-shaped trough wall, waterfalls may form after deglaciation, as in Yosemite and Yellowstone national parks in the western United States. read more

The flow of the Merced River may also be responsible for deepening the Yosemite Valley to create the hanging valleys and waterfalls above. Another example of a hanging valley is found at Glacier National Park in Montana. A hanging valley feeds the Birdman Woman Falls that drop down to Logan Creek in a larger valley below. read more