A valley is an area of elongated lowland, typically surrounded by much higher hills or mountains. It is one of many geological features that make up the surface of the Earth, and it is of special interest and importance to humans, thanks to the fact that valleys have a number of uses. This landform is also quite abundant.
Some geologists break up valleys by type on the basis of how they are formed. A rift valley is formed through separation of the Earth's crust, caused by violent tectonic movements; a notable example is the Great Rift Valley in Africa. A glacial valley is on that has been formed by a glacier; they are especially common in Europe and have a distinctive U-shaped profile when viewed in cross-section. River valleys are formed through the slow process of erosion by water over the course of centuries, and they typically have a V-shaped profile.
Unlike a canyon, a valley is broad, with a large area of floor, rather than a narrow profile. Valleys are generally easy to navigate, and they tend to have a different climate than the surrounding area. It is also common for them to have rich deposits of alluvial mud, making these areas ideal for agriculture. As a result, many human civilizations have settled in valleys, taking advantage of the rivers which often wind through them as a source of water.
Viewed from overhead, a valley often stands out from the surrounding terrain because it has different plant life than the surrounding hills and mountains. This can cause the area to appear lighter in color than the surrounding land, especially when the valley has been cultivated or shaped by humans in some way. The sloping sides also tend to give it away, leading the eye to the deepest part of the floor.
Valleys also have unique weather because their sloping sides can trap hot air, causing the area to warm up considerably in the summer. A valley may also act to trap fog and low-lying clouds, creating a very misty environment. People who live there often bemoan their unique weather, with some people choosing to live on the sloping sides to avoid the stagnant weather conditions which may abound at the floor.