How do tsunamis form?
Tsunamis form in the ocean depths when there is a oceanic earthquake, landslide or eruption of lava flow. These catastrophic level events (there must be sufficient force to trigger a tsunami) upheave the ocean waters resulting in a massive movement of water from the point of disturbance origin, e.g., the earthquake epicenter, outward toward the further boundary of the ocean waters, in other words, toward shorelines. The mighty force behind the "wave train," the series of waves that constitute a tsunami, as opposed to a single "tidal wave," moves at astounding speeds across an entire ocean without losing significant force to reach landfall with virtually full power.
While tsunamis are difficult to visually identify out on the ocean surface, once the initial wave of the tsunami wave train comes to the beginning of land, the lower depths of water have motion retarded while the upper levels continue at full speed. This is when the tsunami is detectable visually since tsunami waves can reach 10 to 100 feet above sea level. It is this massive, unretarded force and speed, which comes crashing and sweeping over land, that causes the destruction as it makes landfall in a train of massive waves, the first one of which not necessarily being the most destructive one. Within the last ten years, new detection experiments have been begun in the Indian Ocean in the hopes of developing an advance tsunami detection and warning system based upon technology similar to seismological detection technology.