A Brief History
On July 9, 1958, an earthquake (7.9 to 8.3 on the Richter scale) struck Alaska, shaking off a 90 million (long) ton block of rock and ice into Lituya Bay in southern Alaska, resulting in the biggest wave ever recorded.
A megatsunami is created when an impact event occurs, such as a meteor striking the water, a landslide causing large amounts of material to fall into the water, or violent volcanic activity. This differs from normal tsunamis that originate from volcanic or tectonic activity on the sea floor, while megatsunamis events are created by impact with the water.
The Lituya Bay incident only killed 5 people, as it happened at a rugged part of Alaska’s southern strip. There were 2 incredibly lucky fishermen in their boat on the Bay when the megatsunami happened, and they lived to tell about it. Incredibly, the giant wave carried their boat over land, high above the trees, and then washed them back into the Bay.
Of the 5 deaths, 2 occurred when an anchored fishing boat was hammered with the massive wave and 3 happened on Khantaak Island. What infrastructure there was in the area was damaged or destroyed.
The giant block of ice and rock that plopped into the water consisted of 30 million cubic meters of material, and weighed 90 million metric tons. If you drop a brick into a wading pool and see the proportionate splash that develops, you can get an appreciation for what an enormous block of ice and rock would do.
This sort of event has happened throughout geologic history, including the one that hit the Yucatan Peninsula 65 million years ago (asteroid versus Earth) that sent waves 5 kilometers (over 3 miles) high! Other megatsunamis in modern times have killed far more people than the Lituya Bay event, even with waves “only” 300 feet high.
These events can occur in lakes as well as the ocean, and in 1980 the eruption of Mt. St. Helens in Washington (state) caused a megatsunami in Spirit Lake with a wave 853 feet high.
Obviously, megatsunamis will happen again, and possibly without warning. There is not much we can do about the big ones, except perhaps live far from the water. Where one hits next, we will have to wait to read about it in History and Headlines.
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