Beachgoers' Double Tsunami Whammy

Just as vacationers' thoughts turn once again to the beach, scientists are warning of a seaside hazard beyond those of tooth and claw and tentacle. The tsunami, that massive wall of water known to coastal residents around the earthquake-prone Pacific, might also be triggered in the quiescent Atlantic by undersea landslides and extraterrestrial impacts.

In the May issue of Geology, marine geologist Neal Driscoll of the Woods Hole Oceanographic Institution in Massachusetts and his colleagues report that they have discovered 50-meter-deep cracks along a 40-kilometer section of the continental shelf off southern Virginia and North Carolina. The shelf edge beyond the cracks appears poised to slip into the abyss, following about 150 cubic kilometers of nearby shelf that made the plunge near the end of the last ice age. When a submarine landslide of similar proportions peeled off the Grand Banks in 1929, notes Driscoll, it created a 4- to 12-meter-high tsunami that killed 51 Newfoundlanders.

Driscoll and his colleagues can't yet set the odds of a new killer wave. But scientists at the University of California, Santa Cruz, have calculated the likelihood of an Atlantic tsunami from another source--a comet or asteroid. Geophysicist Steven Ward and planetary physicist Erik Asphaug estimate, in the May issue of Icarus (see ScienceNOW, 23 November 1999), that there's a 1-in-47 chance over the next 1000 years that a foreign body at least 60 meters across will splash into the Atlantic and send a tsunami greater than 5 meters high rolling over New York City.