the water height reached 656 feet; then as the wave passed Cenotaph Island, it cleared trees to a height of about 160 feet, before hitting them and tossing their boat over the sand spit at the mouth of the harbor.

Aerial photographs taken after the earthquake show the mountains on the north and south sides of the bay swept clean of trees and vegetation. Water surged to a height of 1,700 feet as it poured over the fingers enclosing the bay, stripping off the trees and topsoil down to bare bedrock. Geological records and examination of tree-growth rings show that this was not the first time a giant wave has coursed through Lituya Bay; apparently large waves occurred in 1854, 1874, 1899, and 1936. Recently, scientists have developed various wave models for the bay to predict what wave height could occur under various scenarios. They conclude that a 1,700-foot-high wave is indeed possible.16

Volcanoes are another source of tsunami; at least 92 cases have been documented.17 Of these, the most famous is the eruption of Krakatau (Krakatoa) on August 27, 1883. Following a series of lesser eruptions and explosions for several days preceding the 27th, the volcano finally destroyed itself in an immense explosion that literally echoed around the globe. In the Sunda Straits nearby, ships were lost, 165 villages were destroyed, and more than 36,000 people were killed along the coasts of Java and Sumatra, mostly by two extreme waves that followed when millions of tons of debris were dislodged into the sea. These tsunami had periods of one to two hours. Many towns were only about 33 miles from Krakatoa, so there was no way a warning could have been issued. In addition, since the volcano had been erupting periodically for days, people became complacent. But when it finally blew up, within minutes the town of Merak on the island of Java was hit by a wave 100 feet high. In Merak the wave destroyed stone buildings on top of a hill that stood 115 feet high. Lighthouses toppled, a naval vessel was picked up in the harbor and carried several kilometers inland, and from the high water marks, it appears that the largest wave ran up at least 133 feet when it hit the shore.18

TSUNAMI WARNING SYSTEMS

In its most elementary form, a tsunami warning center has three major components: seismographs to detect if an earthquake capable of caus-



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement