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Silent surge


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POSTED: Wednesday, October 14, 2009

An 8.0-magnitude earthquake near Samoa generated a 6- to 8-foot wave in Keauhou Bay on the Big Island on Sept. 29, witnesses and photos suggest.

The photos, circulating in e-mails and on the Internet, were taken by Kurt Bell, a captain with Fair Wind Cruises, a snorkeling tour company with offices overlooking Keauhou Bay.

Bell said he was on board the Hula Kai, a hydrofoil catamaran, about to come into the bay, when the company's sister catamaran, Fair Wind II, radioed about a tidal surge in the bay at about 2:25 p.m.

The bay calmed down a few minutes later, and the Hula Kai docked and dropped off passengers.

While at the pier, Bell said he felt another wave and took his boat back out to its mooring in deeper water.

At about 3:25 p.m., Bell said he was on shore with other company employees when the water level in the bay dropped, and he began taking pictures from the Fair Wind offices.

“;We were all kind of impressed by it,”; Bell said. “;It was pretty amazing, this incredible force.”;

The water dropped about 3 to 4 feet, and then the surge came in, covering the pier and flooding the parking lot. The water rose to the doors of cars in the parking lot before retreating, Bell said.

“;It wasn't a big breaking wave, the ocean kind,”; he said. “;The water just rose up.”;

He said a fourth, smaller wave came in at about 4:30 p.m.

Scientists at the Pacific Tsunami Warning Center have seen the photos and are intrigued.

“;It looks much larger than what we saw elsewhere,”; said Charles “;Chip”; McCreery, director of the center.

The center issued an advisory on Sept. 29 warning that coastal areas in Hawaii could experience sea level changes and unusual currents from about 1 to 7 p.m. But the largest surge recorded that day was about 2 feet in Haleiwa Harbor, McCreery said.

There are no gauges in Keauhou Bay, McCreery said, but they are now considering adding one.

McCreery explained that wave energy from the tsunami can be refracted by the shape of the islands and “;bounce”; around for several hours.

“;There are places where two or even three waves just happen to come together at the same time,”; he said.

The size and location of a tsunami surge depend on several factors, including the shape of the ocean floor, tides, the direction of the tsunami and the period and speed of the wave, McCreery said.