Nothing approaching last week"s toll of death and destruction has visited European or U.S. shores, but that doesn"t mean they are invulnerable. Large tsunamis are not that rare 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 on the island of Hawaii before moving on to kill at least 100 on the Japanese island of Honshu. Four years later, a tsunami triggered by an earthquake off the coast of Alaska resulted in more than 100 deaths there. The worst European tsunami in recorded history occurred in 1755, when an earth quake off Portugal"s Atlantic coast sent gigantic waves crashing into Lisbon. Together, the quake, the waves and fire took 60,000 lives in the city at a time when it was the cap ital of an empire. Similar death tolls were recorded in towns along Italy"s Strait of Messina in the wake of the tsunami of 1908. The more scientists look into the tsunami threat beyond Asia, the larger it seems to loom. Tsunamis can be triggered by massive landslides as well as earthquakes, and University of Hawaii oceanographer Gary McMurtry has evidence to suggest that around 120,000 years ago, a landslide unleashed by Mauna Loa created a megatsunami that heaved sand and sea fossils 500 m up the slopes of nearby Kohala. Sand layers along the coasts of the North and Norwegian seas and the northeastern Atlantic Ocean have been attributed to a huge tsunami created by an underwater landslide off Norway some 7,100 years ago. In the Canary Islands today, the unstable western slope of the Cumbre Vieja volcano poses a threat to Atlantic coastlines. Should it collapse and slide into the sea, a scientist from University College London warns, it would send tsunamis coursing through the Atlantic basin at hundreds of miles per hour. According to one nightmare scenario, the island chain would be wiped out, and massive waves would strike the west African coast, European countries lying along the Atlantic, northern South America, Caribbean islands, southeastern Canada and the U.S. East Coast. Some waves could be as tall as five-story buildings. Tsunamis take time to travel, which can give populations in harm"s way anywhere from a few minutes to many hours to flee. For this reason, 26 countries have banded together to establish a tsunami-warning system for the Pacific (though not yet for the Atlantic or Indian oceans, or the Mediterranean Sea). "Tsunamis are low-probability, high consequence events," says Viacheslav K. Gusiakov, head of the Russian Academy of Sciences" Tsunami Laboratory in Novosibirsk, Siberia. "But even we specialists on hazards could not quite believe that today a tsunami could kill so many. We used to think of vulnerability in terms of material damage, rather than loss of human life. This great tragedy showed we were wrong." As presently configured, the warning system is far from perfect, generating a 75% rate of false alarms. But that should change with the deployment of a new generation of buoy-anchored detectors that can be positioned deep underwater. In November 2003, a trial run of the system showed that a tsunami unleashed by an Alaskan earthquake would be too small to do any damage when it reached Hawaii—there by avoiding an unnecessary and costly coastal evacuation like one caused by a false alarm eight years earlier. After last week"s disaster, however, few are likely to ignore the tsunami sirens the next time they sound.
单选题
The fact that tsunamis appear more worrisome results from