A pit crater (also called a subsidence crater) is a depression formed by a sinking of the ground surface lying above a void or empty chamber, rather than by the eruption of a volcano or lava vent. It is often found in chains or troughs, which may merge into a linear alignment and usually lack an elevated rim. They also lack ejected deposits and the lava flows that are associated with impact craters.
As distinct from meteor craters, these craters are not formed from the clashing of bodies or projectiles from space. Rather, they can be formed by a lava explosion from a bottled up volcano, the explosion leaving a shallow caldera, or the ceiling over a void may not be solid enough to prevent the collapse of the overlying material. A pit crater also could result from the collapse of lava tubes, dike swarms, or from collapsed magma chambers under loose material.
The process happens frequently on Mars but rarely on Earth. Hawaii is known for its volcanoes and pit craters. In 1868 an eyewitness saw more than two-thirds of the basin of Kilauea cave in and fill with a lava lake. This process happened repeatedly. The modern Halema'uma'u Shield began growing and then collapsed into a deep funnel-shaped pit. This pit filled with lava and for 19 years burned continuously, becoming famous as the Hawaiian Fire Pit. In 1924 the lava lake emptied when the walls of the crater cracked and collapsed and filled with water that turned to steam. After a week and a half Halema'uma'u had widened and was 1,700 feet deep. Rocks that were blasted away from the crater can still be seen on the caldera floor.