is a landform
sunken or depressed below the surrounding area. Depressions may be formed by various mechanisms, and may be referred to by a variety of technical terms.
- A basin may be any large sediment filled depression. In tectonics, it may refer specifically to a circular, syncline-like depression: a geologic basin; while in sedimentology, it may refer to an area thickly filled with sediment: sedimentary basin.
- A blowout is a depression created by wind erosion typically in either a desert sand or dry soil (such as a post-glacial loess environment).
- A graben is a down dropped and typically linear depression or basin created by rifting in a region under tensional tectonic forces.
- An impact crater is a depression created by an impact such as a meteorite crater.
- A pit crater is a depression formed by a sinking, or caving in, of the ground surface lying over a void.
- A kettle is left behind when a piece of ice left behind in glacial deposits melts.
- A depression may be an area of subsidence caused by the collapse of an underlying structure. Examples include sinkholes above caves in karst topography, or calderas. or maars in volcanic areas.
- A depression may be a region of tectonic downwarping typically associated with a subduction zone and island arc. Fore-arc and back-arc sedimentary basins fill with sediment from an adjacent island arc, or from continental volcanism and uplift.
- A valley is a type of depression usually carved by erosion.
- An oceanic trench is a deep depression with steep sides located in the ocean floor. Oceanic trenches are caused by the subduction (when one tectonic plate is pushed underneath another) of oceanic crust beneath either other oceanic crust or continental crust.
- A depression may result from the weight of overlying material such as an ice sheet during continental glaciation which is subsequently removed resulting in a basin which slowly rebounds. The area around the ice sheet, though not covered in ice itself, may also be pulled down by the weight of the ice sheet, which is known as peripheral depression. Further from the ice, a forebulge may form, which is curved slightly upward.
- A depression may be a pothole - either a simple roadway depression or a fluvial erosional depression in a river streambed, or area affected by coastal water currents.