( ( The crater ) ( actually ( ( ( ( filled up ) ( with water ) ) ( to ( become ( ( a ( crater lake ) ) ( for ( ( almost ( 2 million ) ) years ) ) ) ) ) ) . ) ) )
(ROOT (S (NP (DT The) (NN crater)) (ADVP (RB actually)) (VP (VBD filled) (PRT (RP up)) (PP (IN with) (NP (NN water))) (S (VP (TO to) (VP (VB become) (NP (NP (DT a) (NN crater) (NN lake)) (PP (IN for) (NP (QP (RB almost) (CD 2) (CD million)) (NNS years)))))))) (. .)))
The crater actually filled up with water to become a crater lake for almost 2 million years.
(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))))))) (. .)))