On the night of July 9, 1958, an earthquake struck Fairweather Fault in the Alaska Panhandle. The result was that about 30.6 million cubic meters of rock were loosened, being thrown from a height of 914 meters down onto the water mass. Here’s a picture so that you can get a perspective on what that means:
The impact generated a tsunami that crashed against the shoreline of Gilbert Inlet. The water hit with such power that it totally destroyed the spur of land that separates Gilbert Inlet from the main body of Lituya Bay and continued its road towards the Gulf of Alaska. It destroyed all vegetation from elevations as high as 500 meters, uprooting millions of trees. It is the biggest wave ever known to man.