Tsunami

A tsunami is not a single wave, but a series of travelling ocean waves generated by geological disturbances near or below the ocean floor. With nothing to stop them, these waves can race across the ocean like the crack of a bullwhip, gaining momentum over thousands of miles.

The waves are generated when geologic forces displace sea water in the ocean basin. The bigger the earthquake, the more the Earth's crust shifts and the more seawater begins to move.
In a tsunami, waves typically radiate out in directions opposite from the seismic disturbance. In the case of the Sumatra quake, the seismic fault ran north to south beneath the ocean floor, while the tsunami waves shot out west and east.

Tsunamis are distinguished from normal coastal surf by their great length and speed. A single wave in a tsunami series might be 161km long and race across the ocean at 966kmh. When it approaches a coastline, the wave slows dramatically, but it also rises to great heights because the enormous volume of water piles up in shallow coastal bays. -- AP

Pictorial explanation of formation of tsunamis

The confirmed deaths in a mammoth Asian quake and tsunami soared to 58,000 on Wednesday as worst-hit Indonesia readied bulldozers to dig mass graves for corpses in a rush to ward off disease, which the UN health agency said could double the toll.
The earthquake occurred at a spot where the Indian Ocean plate is gradually being forced underneath Sumatra, which is part of the Eurasian plate, at about the speed at which a human fingernail grows.

Did RJ physics dept predict that a tsunami will form? It's something the physics teachers can brag about next year..