- This article is about the physical-geographic term. For places named "Valley" see Valley (disambiguation).
A valley is a landform, which can range from a few square miles (square kilometers) to hundreds or even thousands of square miles (square kilometers) in area. It is typically a low-lying area of land, surrounded by higher areas such as mountains or hills.
Valleys are formed by numerous geographical processes. Glacial valleys, which are usually U- rather than V-shaped, were formed tens of thousands of years ago (most likely during the last Ice Age) by the massive erosive power of glaciers. Several glacial valleys can be found in the English Lake District and many can be found in Alpine countries. Rift valleys, such as the Great Rift Valley, are formed by the expansion of the Earth's crust due to tectonic activity beneath the Earth's surface. Valleys are, however, most commonly formed by fluvial activity (the action of running water, such as rivers), which erodes the landscape.