I find it all really fascinating.

As some of you may know i'm a student and study Geography/Earth Science so i know tsunamis and earthquakes like the back of my hand.

Anyone here who goes fishing or boating will know the effects of the moon on the earth both centrifugal and gravitional forces.

These forces determine how tidal currents move around the earth or upwelling of water. With such a larger force in place with this supermoon this effect on tide with exacerbated.

Of course you all know since you get them in the US that earthquakes are formed by plates moving part, sliding past each other or moving together.

I'd imagine that the plates in the ocean around Japan are convergent plate boundaries i.e. two plates are pushing together and one is submerged - oceanic vs continental plates.

Large forces obviously cause large waves and the combination of the moons effect causing a swelling of tide probably on the eastern side of Japan is most likely what is responsible for the tsunami which occurred.

If there was no supermoon this wouldn't have been as devastating.

As for the whirlpool i'm not sure, i am sure ekman spiral/coriollis force and different forms of wave motion on the surface, below the surface as turbulent flow and on the bed as laminar have something to do with it? They are at least formed by fast flowing water.

In the future this will definitely be studied and if you look at tidal data i'd imagine that in the areas around Japan and to the north, west and south there would have been a drop in tidal height due to the movement of water towards the east.

Just putting it all into context for you :p