(S (S (NP (BASENP (DT The) (NN reason)) (PP (IN for) (NP (BASENP (DT the) (NN cave-in)) (PP (IN of) (BASENP (DT the) (NN roof)))))) (VP (VP (VBD was) (ADVP (RBS most) (RB likely))) (BASENP (JJ massive) (NNS snowfalls)))) (PERIOD .))