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A crater is a landform consisting of a hole or depression on a planetary surface, usually caused either by an object hitting the surface, or by geological activity on the planet. A crater has classically been described as: "a bowl-shaped pit that is formed by a volcano, an explosion, or a meteorite impact". On Earth, craters are "generally the result of volcanic eruptions", while "meteorite are common on the Moon, but are rare on Earth".
A 1961 New Scientist article speculating on the later-dismissed theory that the craters on the Moon might be volcanic in origin noted that "craters produced by volcanism are blessed with advantages of terrain and mineralization not found on impact craters". A crater may become a crater lake if conditions are suitable.John Arthur Thomson, Mountain and Moorland (1921), p. 33. This requires that the crater have relatively even and solid walls, and a source of water such as floodwaters, rain, snow, springs, or other groundwater.
Impact craters are the dominant geographic features on many solid Solar System objects including the Moon, Mercury, Callisto, Ganymede and most small moons and . On other planets and moons that experience more active surface geological processes, such as Earth, Venus, Europa, Io and Titan, visible impact craters are less common because they become erosion, buried or transformed by tectonics over time. Where such processes have destroyed most of the original crater topography, the terms impact structure or astrobleme are more commonly used. In early literature, before the significance of impact cratering was widely recognised, the terms cryptoexplosion or cryptovolcanic structure were often used to describe what are now recognised as impact-related features on Earth.
Pit craters are often found in a series of aligned or offset chains and in these cases, the features is called a pit crater chain. Pit crater chains are distinguished from catenae or by their origin. When adjoining walls between pits in a pit crater chain collapse, they become troughs. In these cases, the craters may merge into a linear alignment and are commonly found along extensional structures such as fractures, fissures and graben. Pit craters usually lack an elevated rim as well as the ejecta deposits and that are associated with . Pit craters are characterized by vertical walls that are often full of fissures and vents. They usually have nearly circular openings. (2025). 9780940295124, Hawai'i Natural History Association. ISBN 9780940295124
Subsidence craters are created as the roof of the cavity caused by the explosion collapses. This causes the surface to depress into a sink (which subsidence craters are sometimes called; see sink hole). It is possible for further collapse to occur from the sink into the explosion chamber. When this collapse reaches the surface, and the chamber is exposed atmospherically to the surface, it is referred to as a chimney. It is at the point that a chimney is formed through which Nuclear fallout may reach the surface. At the Nevada Test Site, depths of were used for tests. When the material above the explosion is solid rock, then a mound may be formed by broken rock that has a greater volume. This type of mound has been called "retarc", "crater" spelled backwards.
When a drilling oil well encounters high-pressured gas which cannot be contained either by the weight of the drilling mud or by blow-out preventers, the resulting violent eruption can create a large crater which can swallow a drilling rig. This phenomenon is called "cratering" in oil field slang. An example is the Darvaza gas crater near Darvaza, Turkmenistan.
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