Computer scientists Galen Gisler and Bob Weaver used Los Alamos' Blue Mountain supercomputer and Lawrence Livermore National Laboratory's ASCI White supercomputer to run the simulations.

After three weeks of computing — the equivalent of more than million hours of individual processor time — they were able to work out the fine details of ocean impacts ranging from a quarter kilometer to a full kilometer in diameter. Their imaginary asteroids also ranged in density from heavy iron to lighter-weight rocks.

"One kilometer is about the threshold for global effects," said asteroid researcher Daniel Durda of the Southwest Research Institute in Boulder, Colo.

The model showed that a one kilometer iron asteroid strikes with the power of 1.5 trillion tons of TNT and produces a spout of water more than twelve miles high, said Gisler.

The simulation also confirmed what was shown in the movie Deep Impact: a big asteroid can produce tsunamis large enough to inundate huge areas. There's even evidence in the Yucatan that the dino killer asteroid that struck there 65 million years ago caused tsunamis that washed over large areas of land, Durda said.

But the real concern isn't just the big impacts, said Durda. Even a moderate to small chunk of rock from space could cause a lot of trouble when it hits the oceans, he pointed out.

For instance, on land, a relatively small, 30 to 50-meter-wide asteroid would create quite a crater and a blast what would cause local damage. The same event in the sea, however, would cause waves that would scour a much larger area, Durda said.

"We know that the timescale of impacts (makes them) common enough that it warrants our attention," said Durda.