July 10, 2007 — A stealthy tsunami which defied nature's own alert system and killed more than 600 last July may have been caused by an undersea landslide, itself triggered by a large earthquake, say scientists.
A team of researchers personally surveyed the devastation on the south shore of Java a week after the July 17, 2006, event. They found that the tsunami hit a relatively narrow 186-mile section of coastline and reached horrific flow depths on land of 20 to 30 feet.
Yet the offshore 7.8-magnitude earthquake associated with the event was barely felt by the Javanese, and there was little noticeable withdrawal of the water along the coast just before the tsunami — two of nature's clearest signs that a tsunami is coming.
"For the people on the shore, they barely felt the earthquake," said Hermann Fritz, a member of the International Tsunami Survey Team and a researcher at the Georgia Institute of Technology. Not that shaking alone would be all that convincing, he said. "In some places where earthquakes are so common, you get used to them."
As for the drawdown of water along the shore, lifeguards who were on duty on the beach of the tourist resort town of Pangandaran reported nothing unusual about the water levels before the tsunami.
"Lifeguards sitting on elevated concrete towers had difficulties in recognizing the initial ocean withdrawal," wrote Fritz and his colleagues in a paper published in the latest issue of the journal Geophysical Research Letters. "A lifeguard reported that, mercifully, the tsunami hit on Monday afternoon, when there were few tourists on the beaches compared to the preceding Sunday."
