The matter of large tsunamis come up in another thread on thermonuclear explosions. Very large earthquakes Mag 8 and greater, produce energies well above the largest manmade thermonuclear detonation. They can also create large tsunamis. The 1964 earthquake produced large tsunamis in Alaska and the northern Pacific. I thought we had discussed this in a thread here, but I can't find such a discussion. 1 Mag 9 earthquake ~ 900 Mag 7 earthquakes USGS has a number of articles on the 1964 Great Alaska earthquake. http://www.aeic.alaska.edu/quakes/Alaska_1964_earthquake.html http://earthquake.usgs.gov/earthquakes/states/events/1964_03_28.php [Broken] There was a large tsunami in Lituya Bay, Alaska in 1958. A large landslide at the head of the bay caused an immense tsunami in the bay. Such large earthquakes could happen in the future since the subduction of the Pacific Plate at the Aleutian Trench is ongoing.