Astrophysicist Jack Hills of the U.S. Department of Energy's Los Alamos National Laboratory presented his findings today at a news conference and a scientific session at the Washington, D.C., meeting of the American Astronomical Society.
A tsunami is a fast-moving ocean wave, usually caused by underwater earthquakes or volcanic eruptions, that runs up on a coastline, causing widespread damage. A tsunami retains its destructive energy while it travels enormous distances. When the wave strikes a continental shelf, its speed decreases and its height increases. An asteroid impact would induce a series of waves that could scour thousands of miles of coastline with walls of water and roiling debris.
Hills and his colleague Charles Mader use a detailed numerical simulation with a one kilometer spatial resolution and comparative data from historical tsunami events.
The Los Alamos model estimates that an asteroid three miles across hitting the mid-Atlantic would produce a tsunami that would swamp the entire upper East Coast of the United States to the Appalachian Mountains. Delaware, Maryland and Virginia would be inundated, including Long Island and all the coastal cities in this region. It would also drown the coasts of France and Portugal.
Alternately, Hills' model shows how much of Los Angeles and Waikiki would be lost if the same rock cratered the ocean between Hawaii and the West Coast.
Fortunately, Earth is likely to take a hit from an object that large only once every 10 million years. However, the chance of a strike by a relatively small asteroid is two or three thousand times more likely, or once every few thousand years.
Objects larger than about 600 feet across are virtually unaffected by the atmosphere and will reach Earth's surface at nearly full velocity to cause a crater on land or sea. Most of the damage from such an impact would come from a tsunami.
For example, the Los Alamos model shows that an asteroid about 1,300 feet in diameter would devastate the coasts on both sides of the ocean with a tsunami more than 300 feet high.
Asteroids smaller than the threshold 600 feet across lose most of their energy in the atmosphere but can still cause unprecedented damage. A "small" impactor hit near the Tunguska River in central Siberia in 1908. Though it never hit the ground, the shock wave flattened 800 square miles of forest.
An impact like Tunguska, which hit with a force a thousand times greater than the Hiroshima bomb, occurs over land every 300 years on average. Hills and Mader have received Laboratory funding for an additional three years of model development. They expect increasingly sophisticated models to predict more extensive coastal damage than previously calculated. And Hills would like to see the research yield a practical plan of defense. "An impact from the smaller asteroids is one disaster that is preventable," Hills said.
But to deflect an asteroid on a collision course, first it must be seen ahead of time. Then a nuclear-armed rocket must be ready to intercept it. A nuclear blast in space could either shatter or re-direct the incoming asteroid, Hills said. Currently, there is no such surveillance or defense capability in place.
"It's a problem that could be solved for much less than the cost of one hurricane. We could just set it up and be done with it," said Hills.
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy.