Craters can either be formed by explosion or collapse. In a volcanic explosion, hot gasses build up to a high pressure and may blow away the material that forms on the top or side of the crater. Collapsed craters are formed when pressure of the molten rock, or magma inside the volcano can't support the weight of the rock or lava above any more. The material that is no longer supported collapses into the space that used to have magma there. An example of craters formed by collapse are ones found at the summit of Mauna Loa.
Calderas are pits in the ground over one kilometer in diameter.
Kilauea Caldera is an example of a Caldera. It is found at the summit crater of Kilauea. It is a special Caldera because inside it is Halemaumau Crater, which used to be the site of a lot of volcanic activity in the late 1800 hundreds and early 1900 hundreds. A picture of Kilauea Caldera and Halemaumau Crater are shown to the left.