Erosion moves material down the slopes to the valley floor where the stream carries it to a lake or to the ocean. In addition, the stream may erode its channel deeper. Hanging valleys are usually formed when erosion is greater in the main valley than in the side valley. A rift valley may form when a long, narrow section of the earth's crust sinks. One system of rift valleys extends from the Sea of Galilee south through the Red Sea, and into southeastern Africa.
Glaciated valleys are valleys enlarged by the action of glaciers.
H. J. McPherson, Ph.D., Former Professor of Geography, Univ. of Alberta. How to cite this article.