A young tsunami survivor is loaded on a rescue plane as he calls for his mother at the destroyed village of Sissano, Papua New Guinea on July 19.
AP/Brian Cassey
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New cause for killer waves in New Guinea?
UPDATE POSTED 24 AUG 1999 Many scientists now think that an undersea slide, not an earthquake, caused the three deadly tsunamis that ravaged Papua New Guinea on July 17, 1998. According to a Science News report, drill cores and photos of the seabed, taken in January and February of 1999, showed signs of repeated slumps. The seabed slopes steeply just offshore of the stricken villages, and slow-moving slumps and faster-moving landslides are common.
There's no question that a significant quake preceded the tsunamis, but scientists have been wondering since the tsunamis hit how a relatively mild (magnitude 7.1) quake could account for the giant, destructive waves.
Science News (see "Seabed Slide Blamed…" in the bibliography) quoted David Tappin, a marine geologist with the British Geological Survey in Nottingham, England as saying "There is no doubt that there is a shift -- a sea change -- in interpretation" in favor of a slump. Tappin was a co-leader of the research team whose results were reported in the July 27 edition of the journal Eos.
The slump theory sidesteps several problems that arise from trying to blame the New Guinea waves on an earthquake alone.
- How could a moderate quake trigger 15-meter-high waves? It didn't directly. Instead, it destabilized rocks and mud that slid down the steep hillside and displaced enough water to cause the giant waves.
- Why was there a 20 minute delay between the quake and the tsunamis? Slumps commonly follow earthquakes by several minutes.
- Computer models of the waves worked better if a slump, not a quake, was the cause.
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