( ( Pillow lavas ) ( ( ( can also ) ( form ( when ( flows ( enter ( a ( ( river or ) lake ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Pillow) (NNS lavas)) (VP (MD can) (ADVP (RB also)) (VP (VB form) (SBAR (WHADVP (WRB when)) (S (NP (NNS flows)) (VP (VBP enter) (NP (DT a) (NN river) (CC or) (NN lake))))))) (. .)))
Pillow lavas can also form when flows enter a river or lake.
(ROOT (S (NP (NP (NNP Lava)) (SBAR (WHNP (WDT that)) (S (VP (VBZ enters) (NP (DT the) (NN water)))))) (VP (VBZ is) (VP (VBN called) (NP (NN pillow) (NN lava)))) (. .)))