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The Honolulu Advertiser
Posted on: Sunday, February 28, 2010

Hilo's location gives almost any tsunami added punch

By Andrew Gomes
Advertiser Staff Writer

Hilo, regrettably, is regarded as the tsunami capital of the United States.

That's bad for the Big Island's capital city and primary population center, but there's good reason for the distinction.

Hilo's position in the Pacific Ocean, its low-lying and well-populated shoreline, and its big bay make it more susceptible to devastating tsunami waves than other places in Hawai'i or the Mainland, according to the Pacific Tsunami Museum.

Destructive tsunamis seemingly home in on Hilo, history has showed. And again, much of the initial concern and focus yesterday were on a town otherwise known for its rainfall.

To be sure, tsunamis have killed or threatened people in other parts of the state. They're a danger for any shoreline, because tsunami waves wrap around islands.

During a tsunami in 1946, the ocean surge reached 54 feet inland on Moloka'i and 55 feet in Polulu Valley on the Big Island's North Kohala coast. In some areas, the surge reached more than a half-mile inland, according to the museum.

In 1975, an earthquake in Volcanoes National Park was quickly followed by another quake two miles off the Big Island, which generated a tsunami, according to the museum. Within 30 seconds of the second quake, the first of five tsunami waves struck, killing two people camping in the park area.

Walter Dudley, a professor of oceanography at the University of Hawai'i-Hilo, said the topography of the ocean floor pretty much steers tsunamis to Hilo from common sites of tsunami-making earthquakes such as Chile to the southeast and the Aleutian Islands to the northeast.

Another major factor is Hilo Bay. The bay's giant mouth, Dudley said, acts to corral and magnify a tsunami's intensity. The effect is as though too much liquid were forced too fast into a sideways funnel. In reality, the front of the fast-moving ocean surge is dramatically slowed by the increasingly shallow bay and then by dry land. Because a tsunami wave is long they can stretch 100 miles frontside to backside the later part of the wave piles up.

"It just keeps coming and coming," Dudley said.

Tsunamis usually are not single waves, but a series of waves. When an initial wave rams into Hilo Bay, it sloshes back and forth, and can result in the next wave having a more chaotic and violent impact, Dudley said.

Tsunami is a Japanese word that translates as "harbor wave."

The 1946 tsunami, which originated in the Aleutians, slammed into the Hawaiian Islands, initially on Kaua'i's north shore and then on down the chain and bending around the Big Island into Hilo. Of the 159 people killed, 96 were in Hilo.

The 1946 tsunami predated Hawai'i's tsunami warning system, so many people were caught off-guard. The impact in Hilo was amplified because of what then was a densely populated neighborhood called Shinmachi near the bay. Today, this area is Wailoa State Park.

Hilo residences and schools now are primarily outside the tsunami inundation zone. However, much of Hilo's commercial core is still susceptible to destruction by a tsunami.

In 1960, a tsunami originating from Chile killed 61 people in Hilo. Dudley said many died because they didn't heed warnings, in part because previous warnings over the years had turned out to be false alarms.

Since 1964, there have been no significant Pacific-wide tsunami events, according to the museum. Dudley also notes that ocean buoys and other more scientific aids deployed in the past 50 years keep people safer than before.

"You don't have to be afraid," he said. "You just have to be prepared."

Even if you're in Hilo.

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