(S (S (PP (VBG According) (PP (TO to) (NP (BASENP (DT the) (NNS people)) (VP (VBG living) (PP (IN in) (NP (BASENP (DT the) (NNS surroundings)) (PP (IN of) (BASENP (DT the) (NN volcano))))))))) (COMMA ,) (S (BASENP (DT the) (NNS rocks)) (VP (VBD were) (VP (VBN released) (PP (JJ due) (PP (TO to) (NP (BASENP (DT the) (JJ huge) (NN amount)) (PP (IN of) (NP (BASENP (NN pressure)) (VP (VBN released) (SBAR (WHADVP (WRB when)) (S (BASENP (DT the) (NN ash) (NN cloud)) (VP (VBD appeared)))))))))))))) (PERIOD .))