Undersea Landslide to Blame for Deadly Wave

H O N O L U L U, July 18 -- Scientists suspect that an earthquake-triggered tsunami that killed more than 2,000 people in Papua New Guinea two years ago on Monday was bolstered by an undersea landslide. It’s a danger that also exists for the U.S. East Coast and Southern California.

It appears the deadly wave in the South Pacific was the resultof an undersea landslide or slump caused by the earthquake whose7.1 magnitude is considered relatively too weak to generate a majortsunami, said Eddie Bernard, director of the National Oceanic andAtmospheric Administration’s Pacific Marine EnvironmentalLaboratory in Seattle.

The tsunami that swept ashore along six miles of coastline anddestroyed four villages was too big and too late to have been thedirect result of the earthquake, he said in a telephone interviewMonday.

Evidence of an Avalanche?

An international team of scientists using multi-beam bathymetricsurveys and manned submersibles to explore the offshore area foundevidence of oceanfloor landslides in August 1998.

“They could see an absence of sediments and exposed rocks thatwould be evidence of a landslide, but there was no previous surveysof the area so it’s only speculation about when it occurred,”Bernard said. “But they are pretty sure it was a recent event.”

The team was able to determine that the first wave hit the shore10 minutes later than would a tsunami generated solely by theearthquake, he said. The biggest wave was more than 40 feet high,according to witnesses.

Earlier this year, U.S. Geological Survey researchers foundevidence of a similar land formation off the Southern CaliforniaCoast.

A team from the Woods Hole Oceanographic Institution discoveredfaults in the ocean floor on the East Coast they say could triggera tsunami, sending 18-foot waves toward the mid-Atlantic states.

Loose Sediment at Most Risk

“These discoveries are drawing our attention to other causes oftsunamis, besides the traditional tectonic earthquake,” Bernardsaid. “The more we learn about possible causes, the better we canknow when to issue warnings.”