(S (S (BASENP (DT A) (ADJP (JJ 10km) (JJ high)) (NN ash) (NN cloud)) (VP (VBD spread) (PP (IN over) (NP (BASENP (DT an) (NN area)) (PP (IN of) (NP (QP (BASENP (NN 740)) (PP (IN by) (BASENP (NN 180)))) (NN km))))))) (PERIOD .))