(S (S (BASENP (NN Lightning)) (VP (VBD was) (VP (VBN observed) (PP (IN within) (NP (BASENP (DT an) (NN ash) (NN cloud)) (SBAR (WHNP (WDT that)) (S (VP (VBD formed) (PP (IN over) (BASENP (DT the) (NN volcano))))))))))) (PERIOD .))