is located in the Aira caldera , formed in an enormous eruption 22,000 years ago. [ 3 [[ http://en.wikipedia.org/wiki/Sakurajima#cite_note-VOWO-2 |]]] Several hundred cubic kilometres of ash and pumice were ejected, causing the magma chamber underneath the erupting vents to collapse. The resulting caldera is over 20 kilometres (12 mi) across. Tephra