( ( ( ( ( ( ( Further expansion ) ( of ( the gas ) ) ) ( ( ( breaks ( ( the ( glass ( bubble walls ) ) ) ( of ( the pumice ) ) ) ) , ) ( ( turning it ) ( into dust ) ) ) ) , ) and ) ( ( ( the ( total mass ) ) ( of ( hot ( gas ( , ( pumice ( , ( glass ( ( shards and ) dust ) ) ) ) ) ) ) ) ) ( ( ( rolls down ) ( the mountainside ) ) ( under ( ( the influence ) ( of gravity ) ) ) ) ) ) . )
(ROOT (S (S (NP (NP (JJ Further) (NN expansion)) (PP (IN of) (NP (DT the) (NN gas)))) (VP (VBZ breaks) (NP (NP (DT the) (NN glass) (NN bubble) (NNS walls)) (PP (IN of) (NP (DT the) (NN pumice)))) (, ,) (S (VP (VBG turning) (NP (PRP it)) (PP (IN into) (NP (NN dust))))))) (, ,) (CC and) (S (NP (NP (DT the) (JJ total) (NN mass)) (PP (IN of) (NP (JJ hot) (NN gas) (, ,) (NN pumice) (, ,) (NN glass) (NNS shards) (CC and) (NN dust)))) (VP (VBZ rolls) (PRT (RP down)) (NP (DT the) (NN mountainside)) (PP (IN under) (NP (NP (DT the) (NN influence)) (PP (IN of) (NP (NN gravity))))))) (. .)))
Further expansion of the gas breaks the glass bubble walls of the pumice, turning it into dust, and the total mass of hot gas, pumice, glass shards and dust rolls down the mountainside under the influence of gravity.
(ROOT (S (NP (NNP Gas) (NN bubble) (NNS holes)) (VP (VBZ helps) (NP (NP (JJ pumice) (NN float)) (PP (IN in) (NP (NN water))))) (. .)))