( ( When ( ( the magma ) ( erupts ( ( rapidly and ) ( explosively ( into ( the air ) ) ) ) ) ) ) ( , ( it ( ( is ( fragmented ( into ( ( small particles ) ( which ( solidify ( into ( VOLCANIC ASH ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT the) (NN magma)) (VP (VBZ erupts) (UCP (ADVP (RB rapidly)) (CC and) (PP (ADVP (RB explosively)) (IN into) (NP (DT the) (NN air))))))) (, ,) (NP (PRP it)) (VP (VBZ is) (ADJP (JJ fragmented) (PP (IN into) (NP (NP (JJ small) (NNS particles)) (SBAR (WHNP (WDT which)) (S (VP (VBP solidify) (PP (IN into) (NP (NNP VOLCANIC) (NNP ASH)))))))))) (. .)))
When the magma erupts rapidly and explosively into the air, it is fragmented into small particles which solidify into VOLCANIC ASH.
(ROOT (S (NP (NP (DT The) (NN thickness)) (PP (IN of) (NP (NN magma)))) (VP (VBZ determines) (SBAR (IN whether) (S (NP (DT a) (JJ volcanic) (NN eruption)) (VP (MD will) (VP (VB be) (ADJP (JJ explosive))))) (CC or) (RB not))) (. .)))