( Tsunamis ( ( can ( be ( formed ( when ( Earthquakes ( happen underwater ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Tsunamis)) (VP (MD can) (VP (VB be) (VP (VBN formed) (SBAR (WHADVP (WRB when)) (S (NP (NNP Earthquakes)) (VP (VB happen) (NP (JJ underwater)))))))) (. .)))
Tsunamis can be formed when Earthquakes happen underwater.
(ROOT (S (NP (DT A) (-LRB- -LRB-) (NN n) (-RRB- -RRB-) (NN underwater) (NN earthquake)) (VP (VBZ creates) (NP (DT a) (NN tsunami))) (. .)))