Jon ran as the tunnel collapsed behind him.
( Jon ( ( ran ( as ( ( the tunnel ) ( collapsed ( behind him ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Jon)) (VP (VBD ran) (SBAR (IN as) (S (NP (DT the) (NN tunnel)) (VP (VBD collapsed) (PP (IN behind) (NP (PRP him))))))) (. .)))
The blast had brought the walls of the tunnel down.
( ( The blast ) ( ( had ( ( brought ( ( the walls ) ( of ( the tunnel ) ) ) ) down ) ) . ) )
(ROOT (S (NP (DT The) (NN blast)) (VP (VBD had) (VP (VBN brought) (NP (NP (DT the) (NNS walls)) (PP (IN of) (NP (DT the) (NN tunnel)))) (ADVP (RB down)))) (. .)))