( ( ( ( ( Calderas ( form ( when ( ( a ( magma chamber ) ) ( ( empties out ) ( its magma ) ) ) ) ) ) , ) and ) ( ( ( the surface ) ( above ( the chamber ) ) ) collapses ) ) . )
(ROOT (S (S (NP (NNS Calderas)) (VP (VBP form) (SBAR (WHADVP (WRB when)) (S (NP (DT a) (NN magma) (NN chamber)) (VP (VBZ empties) (PRT (RP out)) (NP (PRP$ its) (NN magma))))))) (, ,) (CC and) (S (NP (NP (DT the) (NN surface)) (PP (IN above) (NP (DT the) (NN chamber)))) (VP (VBZ collapses))) (. .)))
Calderas form when a magma chamber empties out its magma, and the surface above the chamber collapses.
(ROOT (S (PP (IN After) (NP (DT a) (JJ massive) (NN eruption))) (, ,) (NP (NP (DT a) (NN mountain)) (VP (VBG collapsing) (PP (IN above) (NP (DT an) (JJ empty) (NN chamber))))) (VP (MD will) (VP (VB create) (NP (DT a) (NN caldera)))) (. .)))