FREQUENCY: 100,000 OR MORE YEARS
An asteroid with a diameter of one kilometer (0.6 mile) could completely devastate a land area the size of Europe and blanket Earth with dust. But because two-thirds of Earth's surface is covered by ocean, a more likely outcome would be an enormous tsunami, or "tidal wave."
Roughly 1,100 asteroids of this size have Earth-crossing orbits, and the Spaceguard detection program, supported by NASA, is scheduled to map 90 percent of them by 2008. Only one asteroid found so far has even a minimal—one in 300-chance of striking Earth, on March 16, 2880.
If an asteroid this size landed in the ocean 640 kilometers (400 miles) from New York, waves higher than the Statue of Liberty would hammer the coast from Massachusetts to North Carolina. The waves reaching Africa or Europe would be smaller—only 20 meters (65 feet) high.
Topic: Earth Science
Keywords: Asteroids--Collisions with Earth, Astrogeology, Astrophysics, Collisions (Astrophysics), Meteorites, Natural disasters, Near-Earth asteroids, Tsunamis