A landform is a particular feature of the shaped surface of the Earth. Landforms of all sizes provide clues about past geological processes in a given area. They also can affect current geological processes such as where or how quickly erosion will occur, and they can affect meteorological processes such as rain patterns and flooding in high-risk zones.
Valleys are lowered regions of the Earth's surface. They can be as steep-sided as canyons, or can be gently sloping on both sides with a broad plain at the bottom of the valley. Valleys are often formed from the erosive effect of the movement of water over rock and soil over very long periods of time. V-shaped valleys are often formed from down-cutting, the process by which a moving stream erodes the ground beneath itself. Eventually, V-shaped valleys may widen to form flat-bottomed valleys.
Valleys can also be formed from the movement of glaciers as they pass over the surface, carving away the ground beneath. U-shaped valleys, the third major valley shape, are often formed by glacial erosion, sometimes through previously existing V-shaped valleys. Valleys differ from basins in that when water enters a valley, it has an exit, whereas a basin has no external drain for the water.
Mountains are large vertical landforms that make a striking feature of any landscape. They are defined as a natural elevation of the Earth's surface, usually reaching an altitude of 2,000 feet or more, according to Dictionary.com. Mountain building is called orogenesis.
Many geological processes lead to orogenesis. One of the most dramatic is volcanic eruptions, though not every mountain is formed by volcanic activity, and not every volcano is a mountain. However, when conditions are just right, a volcanic eruption can result in an ever-increasing pile of molten rock, which cools and hardens to form a cone-shaped landform. Mountains can also form as a result of the movement of the giant tectonic plates that cover the Earth's surface. When these plates collide, rock can be displaced and squeezed upward over time, often forming not just one mountain, but an entire range or chain of mountains.
Plains are broad, mostly flat areas of the landscape, although they may have low, rolling hills or a gentle slope. More than 50 percent of the interior of the Earth's continents are composed of plains. Plains sometimes form from uneven landscapes that are covered with layer upon layer of sediments, gradually turning the surface of the Earth flat and even. The bottom of large bodies of water are often quite flat, and if water levels change enough to bring the formerly submerged land to the surface, the resulting land will be a flat plain.