Can you see a tsunami wave out at sea? I thought it was frequently just a one or two foot rise in sea level over a large area, until it starts to pile up as it reaches shallower water.
Tsunamis in the open ocean are rarely visible.
An ocean crossing tsunami can be as small as 1-2 cm in height. In that case the tsunami would be a large volume of water spread out, yet traveling at a high rate of speed up to about 600 mph.