Tidal Wave is an apt description of the process. It looks like a very rapid tide to people who live along the coast-whatever word works for you. Well, in the Pacific Ocean over the last hundred years there has been one destructive Tsunami per year on average. So they are very frequent in the Pacific Ocean. Crakatowa in Indonesia.
Underwater landslides can also generate Tsunamis.
And in some instance earthquake is accompanied by an underwater landslide, so the combination can make a Tsunami larger than the earthquake would produce by itself. That too would produce a Tsunami. Well, that means it's particularly dangerous because the time from-the time the earthquake stops to the Tsunami arrives is very short, giving the residents almost no time to react. But also, it probably made it more efficient. I mean powerful, that is, the transfer of energy from the earthquake to the water was very efficient, because it was near the shore, near the coast line and all the energy went directly into the wave formation.