Enormous eruptions may empty the main vent and the magma chamber beneath a volcano. The mountain becomes a hallow shell. With nothing to support it , the top of the mountain collapses inward. The huge hole left by the collapse of a volcanic mountain is the caldera. The hole is filled with the pieces of volcano that have fallen inward, as well as some lava and ash. An example is Crater Lake in Oregon.

For more information about volcanoes visit these sites. Discovery and Kidscosmos