( ( ( The crater ) ( ( ( gradually ( filled ( with water ) ) ) and ) ( ( is now ) ( a lake ) ) ) ) ( , ( ( ( the surface ) ( of which ) ) ( ( is ( ( 1000 feet ) ( below ( the rim ) ) ) ) . ) ) ) )
(ROOT (S (S (NP (DT The) (NN crater)) (VP (VP (ADVP (RB gradually)) (VBD filled) (PP (IN with) (NP (NN water)))) (CC and) (VP (VBZ is) (ADVP (RB now)) (NP (DT a) (NN lake))))) (, ,) (NP (NP (DT the) (NN surface)) (WHPP (IN of) (WHNP (WDT which)))) (VP (VBZ is) (NP (NP (CD 1000) (NNS feet)) (PP (IN below) (NP (DT the) (NN rim))))) (. .)))
The crater gradually filled with water and is now a lake, the surface of which is 1000 feet below the rim.
(ROOT (S (NP (NNS Craters) (CC and) (NNS rifts)) (VP (VBP become) (NP (NNS lakes)) (SBAR (WHADVP (WRB when)) (S (NP (PRP they)) (VP (VBP fill) (PP (IN with) (NP (NN water))))))) (. .)))