Acaldera a

a. type of volcano
b. type of volcanic eruption
c. very large volcanic bomb
d. large depression in a volcano

A Caldera a "large depression in a volcano".

A caldera is a volcanic component shaped by the collapse of a volcano into itself, making it a vast, extraordinary type of volcanic cavity.  

A caldera collapse is normally activated by the exhausting of the magma chamber underneath the spring of gushing lava, as the aftereffect of a large volcanic eruption.

On the off chance that enough magma is ejected, the exhausted chamber won't have the capacity to help the heaviness of the volcanic structure (the mountain) above.  

Fractures will conform to the edge of the chamber, more often than not in a generally circular shape.  

These ring fractures may in reality fill in as volcanic vents.

is there multiple choice or do you need like an essay answer?