(S (S (NP (BASENP (JJ Pyroclastic) (NNS flows)) (VP (VBG descending) (PP (IN on) (NP (BASENP (DT the) (JJ northwestern) (NN slopes)) (PP (IN of) (BASENP (DT the) (NN volcano))))))) (VP (VP (VBD left) (NP (BASENP (DT a) (NN path)) (PP (IN of) (BASENP (NN destruction))))) (ADVP (RB behind)))) (PERIOD .))