I found the bit about electric currents particularly interesting:-
The vertical movement of waters is a slow process, though. Why do those whirlpools exist for such a long time? This is partially the effect of Earth’s magnetic field. In addition, marine water contains many charged ions, Na and Cl for example. To crown it all, water molecules are dipoles that are charged both positively and negatively. Any dipole starts spinning when moving in the magnetic field. An oceanic ring gathers millions of billions of molecules together. That is why the giant circle movement triggered by the vertical movement of water may last for months and years mechanically. Ions also give more power to the craters. Natrium and Chlorum are charged as well, and their movement in the magnetic field of the Earth also leads to the appearance of the circle movement.