In the intervening millennia, says the University of Hawaii geophysicist, the coastline has built back up and is ripe for a repeat. That doesn't mean it will happen tomorrow, or next year, or even next century.

"Those things happen few and far between, but we cannot ignore them because when they do happen they are so catastrophic that they are sort of culture-ending disasters," says Fryer. "I am pretty much convinced that if there would be a big landslide like that, there would be abundant warning. There would be lots of little earthquakes, and it should be pretty well defined. I think there would be months or even years of warning. But it would still be a catastrophe."

Fryer, who reported on the prehistoric Alika 2 submarine landslide with UH ocean researcher Gary McMurtry in the September issue of the journal Geology, says the resulting tsunami would cover the isthmus of Maui and flood Oahu to the outskirts of Wahiawa. "Basically, Honolulu is removed from the map," says Fryer. Large-scale disasters that happen very seldom -- known to emergency planners as "low-frequency, high-impact events" -- have taken on new interest and urgency in the aftermath of the Dec. 26 Indian Ocean tsunamis.