Giant ocean waves (sometimes called "tidal waves") caused by an underwater earthquake or volcanic eruption.
A wave set up by a submarine earthquake, landslide, or volcanic action. Many such seismic disturbances do not produce sea waves and often those produced are small, but the occasional large wave can be very damaging to shore installations and dangerous to ships in harbors. The destructive wave is commonly referred to as a "tidal wave," a term which is technically incorrect, as it is not the result of tide-producing forces.
A huge sea wave caused by earthquakes. (Referred to by many as a tidal wave.)
Waves generated by seismic activity, sometimes called seismic sea waves. Tsunamis are also popularly, but inaccurately, called tidal waves. When they reach shallow coastal regions, amplitudes may increase to several metres.
When thrust-faulting earthquakes happen under the ocean, the earthquake can push large blocks of ocean floor up. When the ocean floor moves up, the water that was in that spot has to go somewhere else. That somewhere else is into a large wave called a tsunami.