Example of the formation of a caldera, the pictures show Mount Mazama's eruption timeline

Crater Lake in Oregon

A caldera is a volcanic feature formed by the collapse of land surface after a gigantic volcanic eruption. In such an eruption the volcano's magma chamber is empty enough for the ground above it to drop.

A caldera may look like a volcanic crater except that a crater is made by blasting outward, not by collapsing inward. The word caldera comes from the Portuguese language, meaning "cauldron". Some complex features are made by both processes.