Cave In, Collapse, Sinking, Depression
noun, verbal noun
A cave in where everyone dies is still a cave in, just a really sad one.
かんぼつ
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
地震であそこの道路が陥没したそうです。
It looks like that highway over there collapsed from the earthquake.