FAQs about the Natural History of the Inside Passage

4. Do recreational boaters and campers need to worry about tsunamis? Does Alaska have a tsunami warning system? What physical evidence does a tsunami leave along the shores?

Alaska is extremely seismic. The subduction zone created by the Pacific plate sliding under the North American plate makes the coastal areas very dangerous with regard to tsunami generation. For example, more than 90 percent of the deaths in Alaska during the 1964 earthquake were due to the subsequent tsunamis. The 1964 earthquake and tsunami deaths alerted State and Federal officials to the need for timely and effective tsunami warnings and earthquake information. In 1967, the West Coast and Alaska Tsunami Warning System was established in Palmer to provide continuous 24-hour earthquake monitoring.

In Southeast Alaska, the major fault is the Queen Charlotte-Fairweather fault. Although it does have a history of vertical displacements, this fault has not caused large tsunamis seen in other Alaskan areas. However, events occurring in this region have induced large landslides, which in turn, have generated massive local tsunamis. There is also evidence that landslide-induced tsunamis have occurred in this area without an earthquake.

The most amazing example of a massive local tsunami was in Lituya Bay in 1958. A 7.5 magnitude earthquake along the Queen Charlotte-Fairweather fault created a landslide dumping what is estimated to be 40 million yards of earth into Lituya Bay. The landslide generated a giant wave often referred to as the Lituya Bay Tsunami, destroying the vegetation as far as 3,600 feet inland from the shoreline and 1,720 feet up the mountain at the head of the bay. In 1936, a similar wave destroyed the vegetation 490 feet up the slopes of the bay and 2,000 feet inland. There was no evidence of an earthquake in the 1936 tsunami and the exact cause remains a mystery.