found two definitions that made me laugh

[Brian Kelsay]

A book I'm reading about Mars mentioned caldera in relation to volcanoes, so I looked up the term.
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cal·de·ra   Pronunciation (kl-dâr, -dîr, käl-)
n.

    A large crater formed by volcanic explosion or by collapse of a volcanic cone.

caldera  n : a large crater caused by the violent explosion of a volcano that collapses into a depression

[Spanish, cauldron, caldera, from Late Latin caldria. See cauldron.]

Brian Kelsay