1)An Undersea Earthquake - is the most common form of tsunami formation, typically generating the most destructive tsunamis. The earth is constantly moving on large tectonic plates. When these tectonic plates move past each other, collide and/or slide under one another (subduction), an earthquake results. This is what happened with the recent tsunami that devastated Southern Asia. Here, a massive earthquake in the Indian Ocean measuring 10.0 on the Richter scale jolted the seabed causing the sudden displacement of a very large volume of water. The earthquake temporarily produces a fluctuation in the mean sea level of a specified area. Waves quickly form as the displaced water tries to recapture equilibrium by filling the vacuum that was created. It should be noted that not all earthquakes generate tsunamis. Usually, it takes an earthquake with a Richter magnitude exceeding 7.5 to produce a destructive tsunami.