Look at the wave hitting the vertical end of the breakwater. The water has been thrown vertically upwards. This means that a force must have been acting on it in the vertical direction. That's odd if you think that a wave is coming in horizontally and hitting a vertical surface. The contact force between the wave and the surface should act at 90 degrees to the surface and thus act horizontally in the opposite direction to the direction of the wave. I think that the wave itself must have been moving vertically at the time of impact so that it did have some initial momentum in this direction. Also, the end of the breakwater probably isn't truly vertical but I didn't fancy going to find out at the time that I took the photograph. But with lots of news coverage of similar waves at places like Aberystwyth, something is causing the waves to go up vertically.
