Nothing even approaching last week's toll of death and destruction has ever visited U.S. shores, but that doesn't mean North America isn't vulnerable. Large tsunamis are not that rare, especially in the Pacific, and every now and again, they crash into familiar ports of call, sweeping away people and property. In 1960, for example, a tremendous earthquake in Chile unleashed an armada of giant waves that killed 61 people on the island of Hawaii and then moved on to kill at least 100 more on Japan's Honshu Island. Four years later, a tsunami triggered by an earthquake off the coast of Alaska resulted in more than 100 deaths in Alaska, four in Oregon and 13 in California, plus $100 million in property damage along the western coasts of the U.S. and Canada.
And those are just the tsunamis in recent memory. The prehistoric record is more disquieting. Geologist Brian Atwater of the U.S. Geological Survey has assembled compelling evidence that as recently as 300 years ago, huge tsunamis of shocking power pummeled the Pacific Northwest, from California to British Columbia, reshaping coastlines and surging far up rivers and streams. The culprit: an undersea fault in the Cascadia subduction zone that bears more than a passing resemblance to the fault that just ruptured off Sumatra. "There are so many similarities between what happened there and what could happen here," says Vasily Titov, a tsunami modeler with the National Oceanic and Atmospheric Administration in Seattle. "It's not a question of if but when."
The more scientists look into the tsunami threat to North America, in fact, the larger it seems to loom. Hawaii not only sits in the path of tsunamis that are generated around the Pacific--in 1946, a wave unleashed by a temblor off the Aleutians killed some 170 people in the city of Hilo--but it also harbors its own, homegrown threat. Tsunamis can be triggered by massive landslides as well as earthquakes, and University of Hawaii oceanographer Gary McMurtry has evidence to suggest that about 120,000 years ago, a landslide unleashed by the Mauna Loa volcano created a mega-tsunami that heaved sand and sea fossils 1,600 ft. up the slopes of nearby Kohala.
The U.S. tsunami danger is not confined to the Pacific's hyperactive Ring of Fire. In the Canary Islands, the western slope of the Cumbre Vieja volcano poses a threat to Atlantic coastlines. Should it collapse all of a piece, a scientist from University College London warned last week, the big splash would send tsunamis coursing through the Atlantic at hundreds of miles an hour. According to one nightmare scenario, cities up and down the East Coast would be swamped by waves as tall as five-story buildings.