( Tsunami ( ( is ( ( a ( ( very large ) ( ocean wave ) ) ) ( triggered ( by ( ( ( ( ( underwater earthquake ) , ) ( volcanic activities ) ) or ) landslides ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Tsunami)) (VP (VBZ is) (NP (NP (DT a) (ADJP (RB very) (JJ large)) (NN ocean) (NN wave)) (VP (VBN triggered) (PP (IN by) (NP (NP (JJ underwater) (NN earthquake)) (, ,) (NP (JJ volcanic) (NNS activities)) (CC or) (NP (NNS landslides))))))) (. .)))
Tsunami is a very large ocean wave triggered by underwater  earthquake, volcanic activities or landslides.
(ROOT (S (NP (DT A) (-LRB- -LRB-) (NN n) (-RRB- -RRB-) (NN underwater) (NN earthquake)) (VP (VBZ creates) (NP (DT a) (NN tsunami))) (. .)))