Tsunamis are usually formed when there is an underwater earthquake, volcano, or other seismic event. The word tsunami comes from Japanese (one of the most common locations for tsunamis), "Tsu", meaning "harbor" and "nami" meaning "wave".
The most recent tsunami (as of Nov. 1 2009) according to NOAA National Weather Service was on October 7, 2009 , originating from an underwater earthquake near the Vanuatu Islands in the southwest Pacific. The wave affected other islands, including Hawaii and Fiji, as well as Alaska and California.
This tsunami however was extremely weak and insubstantial, compared to one of the most recent (and devastating) tsunamis on December 26, 2004, also known as the Sumatra-Andaman earthquake. The wave itself was in places up to 100 feet (30 meters) high. It was the fifth worst natural disaster in recorded history, and is the deadliest tsunami ever, possibly more than four times worse than the next deadliest tsunami (in terms of death toll, the costs are only rough estimates, ranging from 229,866 to 443,929 people killed).
Tsunamis are incredibly powerful. As well as their massive size, tsunamis are incredibly fast, until they reach the shore. In the open sea, they can reach speeds of over 300 mph (480 kph). In fact, they are so fast, and so wide, from a boat or airplane flying above, they would be practically invisible. They can kill hundreds of people a year, and they are most certainly a force to be reckoned with.
