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Large, bowl-shaped volcanic depression that forms when the top of a volcanic cone collapses into the space left after magma is ejected during a violent volcanic eruption. The term is Spanish for caldron. Subsequent minor eruptions may build small cones on the floor of the caldera which may still later fill up with water; an example is Crater Lake in Oregon.
This entry comes from Encyclopædia Britannica Concise. For the full entry on caldera, visit Britannica.com.