Cosmic Collision Could Crunch Coasts
(From the March/April 1998 issue of StarDate magazine)
Bulletin: Defense Department spy satellites have detected a titanic explosion in the middle of the North Atlantic. A mountain-size asteroid has just crashed into the ocean at thousands of miles an hour, generating waves as tall as a 25-story building.
If you live on the East Coast of the United States, you have three hours to get away before a 300-foot wall of water hits you. Delaware, Maryland, and Virginia will disappear. So will New York City, Boston, and Miami. Waves will lap at the foothills of the Appalachian Mountains. Several hours and several giant waves later, the water will recede. But the great cities will be gone -- scoured clean by walls of water and debris.
That's the scenario outlined by Los Alamos National Laboratory researchers Jack Hill and Charles Mader. They used computers to simulate the giant waves, called tsunamis, that would be created if a large asteroid slammed into the Atlantic or Pacific Oceans.
Scientists have calculated the effects of large impacts on land -- perpetual darkness from the debris blasted into the atmosphere, global acid rain, and creation of a large impact crater. But Hills said this was the first effort to model the effects of an ocean impact.
Although a splash as big as this one (from an asteroid about three miles (five km) across) only happens once every 10 million years or so, smaller asteroids could be dangerous, too. The tsunami from an asteroid just 600 feet (about 200 meters) across could devastate coastal cities, the researchers say. Asteroids of that size slam into Earth once every few thousand years. That means there's about a one in 50 chance that it will happen during the average human lifetime. Asteroids smaller than a football field are likely to vaporize or explode as they enter Earth's atmosphere, so they would not strike the surface.
Tsunamis generated by earthquakes or underwater volcanoes can kill hundreds of people and devastate coastal areas. An earthquake off the coast of Chile in May 1960, Hills said, produced a tsunami that killed at least 114 when it rolled into Japan -- 11,000 miles (17,000 km) to the west.
No tsunamis from asteroid impacts have been recorded in all of human history. But 65 million years ago, the impact that may have killed the dinosaurs triggered a massive tsunami. The impact occurred in the Gulf of Mexico, just off the Yucatan peninsula. Geologists recently found that a wave from the impact swept across much of present-day Texas.
Several groups of astronomers are trying to find and calculate the orbits of all the asteroids that inhabit the inner solar system, and determine if any are on a collision course with Earth. With enough warning, we might be able to deflect the asteroid and prevent a global catastrophe. -- — Damond Benningfield
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