Britannica Sources used in this answer

How do hanging valleys produce waterfalls after glaciers melt?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Snow-capped, rugged Atlas Mountains encircle a green valley with scattered trees, terraced fields, and a few small buildings in Morocco. — valley The rugged Atlas Mountains surround a valley in Morocco.

Hanging valleys are formed through the process of glacial erosion. During glaciation, a large trunk glacier possesses greater ice discharge and erosive power than the smaller tributary glaciers that feed into it. Consequently, the main valley is deepened and widened more rapidly than the tributary valleys.12

When the ice eventually retreats, the floors of these tributary valleys are left at an elevation significantly higher than the floor of the main valley. Because of this discordant junction, streams flowing from the tributary valleys must drop over the steep walls of the main U-shaped trough to join the drainage system below, thereby creating waterfalls. Famous examples of this phenomenon include the waterfalls found in Yosemite National Park and Yellowstone National Park in the United States.123