Glossary: Complex Craters
Complex craters form when a medium-sized impactor (though still much smaller than the target) hits a planetary surface at very fast speeds. The resulting impact produces a large, flat-floored crater.
This kind of crater is too large to support itself, so the sides collapse inward, forming slump terraces along the outer rim, and the floor rebounds upwards, creating a central peak structure. Frequently, the floor of the crater is filled with a thick layer of impact melt, contributing to the flatness of the floor.
Examples of complex craters on the planets