Tidal waves, or tsunami, are waves that differ from winds caused by the gravitational pull of the Moon or oceanic winds. Although also a natural trigger, tidal waves are created by underwater disturbances or above water events. Also, tidal waves are not always a bad thing; it just depends on their size.
Tidal waves are large transmissions of energy that transmit through still water that push outward from the origin, either in the form of an expanding ring of a wall moving in one direction. Though the thought maintains that the water is moving, it is more or less staying in one relative place, while it takes the form of the energy being transmitted through it. The formation of the top of the wave represents the crest, the bottom is the trough, which is in the valley between waves, though some energy movement can happen with only one apparent crest. This energy movement can travel great distances before losing its frequency.
Before losing is frequency, wave energy that finally reaches the shore or shallow waters hits with its trough first. This dragging action against the bottom slows the forward progression, and the energy of the crest overtakes it, causing the wave to push over as a breaker. The breaker is the part of the wave considered the most dangerous aspect of a tidal wave and is the main depiction of such a wave, rather than the otherwise peaceful looking water swell while it was far from shore.
The underwater cause of tidal waves are nearly all from seismic activity or the collapse of undersea mountains, but sometimes a manmade device, such as a nuclear bomb, can create a similar effect. Above water causes can be in part to volcanic activities, failing cliffs, or even landslides into the ocean. Most tidal waves that originate in the Pacific and Indian oceans are caused by underwater earthquakes when the tectonic plates slide underneath the other, causing an upheaval that transmit its energy to the surface. The deadly Indian Ocean tsunami of 2004 was one such event, as a result of a 9.3 Magnitude earthquake off the coast of Indonesia. Although the above water causes are not as common, there is the belief that if an event occurred in the Canary Islands in the Atlantic Ocean off the coast of Africa, the right event could trigger a series of tidal waves large enough to impact the majority of the eastern coast of North America, particularly at along the United States.
Of course, not all tidal waves are dangerous ones. Sometimes underwater earthquakes can occur and the tidal energy that is created in the middle of the ocean is lost as it travels or wasn't sizable to begin with. This low energy then results in a tidal wave that is no larger or even smaller than that of a normal wave. Early detection systems across the world are good for identifying which waves can be considered dangerous, and the response time has improved as well. It is only a matter of time before prevention measures can stop such a wave outright.