[Image] [Image] Double Whammy An asteroid striking land would be catastrophic, but the damage might be far worse if it crashed into the sea. One if on land, two if at sea. That's the [Tsunami animation] Image: Edwin damage assessment for Vigils, Los Alamos National an asteroid hitting Laboratory Earth. Indeed, although an impact on WASHOUT: This simulation shows a land would be tsunami, generated by an asteroid catastrophic, a impact in the Atlantic Ocean, watery one would be inundating a section of the eastern doubly so. Reason U.S. The waves would move far being, towering inland to the foothills of the waves, called Appalachian Mountains. Norfolk, MORE tsunamis, would race Va., the Delmarva Peninsula and EXPLORATIONS outward and crash Cape May, N.J., would be engulfed; down upon the Washington, D.C. would end up on a coastlines, which are tiny island. home to more than half the world's population. At least that is the conclusion drawn from recent computer simulations by researchers at the Energy Department's weapons labs. With real bombs falling out of fashion, these experts have kept their supercomputers humming by simulating enormous natural blasts. Last year, a group at Sandia National Laboratories tested a new computer by modeling the impact of an asteroid. Not to be outdone, a team at Los Alamos National Laboratory recently tackled the aftermath of such a hit. They revealed their findings at a meeting of the American Astronomical Society in early January. The most recent simulation, created by Los Alamos astrophysicist Jack Hills and his colleague Charles Mader, assumes that an asteroid three miles across slams into the mid-Atlantic, thereby creating a series of waves that spreads out from the point of impact. Tsunamis are unlike other ocean waves. In the open sea, they are an almost undetectable swell, often barely inches high. But they can travel thousands of miles in a matter of hours. [Comet animation] When tsunami (from the Japanese COMET IMPACT. characters for "harbor" and "wave") Scientists at reach shallower coastal waters, their Sandia National velocity is slowed, and they rear up Laboratories into immense walls of water that slam modeled a comet into the shoreline and pour far inland. striking the The Los Alamos model shows that the ocean. waves created by an asteroid impact would drown the entire upper East Coast of the U.S. inland to the foothills of the Appalachian Mountains. Delaware, Maryland, Virginia and Long Island would be inundated--and all the coastal cities completely destroyed. The waves would also swamp the coasts of France and Portugal. Earth is likely to take a hit from an object that large only once every 10 million years or so. But the chance of a strike from a smaller asteroid is 2,000 or 3,000 times more likely, or once every few thousand years. The Los Alamos model shows that an asteroid a mere 1,300 feet in diameter would still cause enormous devastation, raking the coasts with tsunami more than 300 feet high. Asteroids smaller than about 600 feet across burn away and lose most of their energy in the atmosphere. But even these smaller strikes are far from innocuous. It was an object of this type that exploded in the air near the Tunguska River in central Siberia in 1908. The Tunguska shock wave flattened 800 square miles of forest; the force of the detonation is estimated to have been 1,000 times greater than the Hiroshima bomb. Although the accuracy of the Los [Tsunami damage] Alamos models can be disputed, the TSUNAMI AFTERMATH: devastating effects of tsunamis are In 1964 an well known, especially to coastal earthquake in dwellers on the Pacific Ocean. There, Alaska's Prince sudden changes in the level of the William Sound seabed, triggered by undersea triggered a earthquakes or volcanic activity, Pacific-wide cause these frequent marauders. Like tsunami. Damage at the waves predicted for asteroid Seward, Alaska, strikes, the potential for damage is included this spread over thousands of miles by the beached ship and waves propagating through the water. demolished truck. Overall the event In just one recent example, more than claimed 122 lives 2,000 people were killed on December and caused more 12, 1992, when a tsunami flooded two than $106 million volcanic islands in the South in damage. Pacific, called Flores and Babi. By the time the waves swept ashore, they were more than 80 feet high. Other tsunamis have struck Alaska and Japan. And some have occurred even in the less seismically active Atlantic Ocean. In 1929 a giant wave roared ashore in Newfoundland, Canada. Only 29 lives were lost--but only because the island was so sparsely populated to begin with. Scientists around the world are working on a variety of methods to provide real-time warnings when a tsunami is headed for land. One program, called CREST for Consolidated Reporting of Earthquakes and Tsunamis, was begun in 1996 by the National Oceanic and Atmospheric Administration (NOAA). Eventually, it will consist of 60 seismic-sensing sites in the U.S. Pacific states. When the instruments detect seismic activity that could generate a tsunami, the data will be flashed to tsunami-warning centers. NOAA is also installing a network of undersea Bottom Pressure Recorders (BPRs) that it hopes will be able to track tsunamis in real time. Japan has a similar project under way. Hill and his colleagues are all in favor of the tsunami warning system, but they believe it does not go far enough. They advocate a similar system to track asteroids and set up missiles carrying nuclear warheads to destroy or deflect them before they endanger Earth. Although we can't do much about the restless motions of our planet, Hill believes we can fend off interlopers from the cosmos. He remarks: "An impact from the smaller asteroids is one disaster that is preventable." --Alan Hall, contributing writer RELATED LINKS: Tsunami! from the University of Washington The National Tsunami Hazard Mitigation Program Asteroid and Comet Impact Hazards site Near-Earth Objects Survey Working Group Spacewatch Project Near-Earth Object tracking ----------------------------------------------------------------------------