Expect Many Waves

Saturday, February 27th, 2010

We often hear stories of a tsunami wiping out a beach, but anyone near the beach should expect many waves:

Just after 10 p.m. on May 22, 1960, seismologist Jerry Eaton and four companions assembled at the U.S. Geological Survey’s Hawaiian Volcano Observatory on the Island of Hawai’i. Gathering cameras, notebooks, flashlights, and steel measuring tapes, they piled into a Ford station wagon for the 30-mile ride down to Hilo. There they hoped to measure the 1960 Chilean tsunami, which was expected to arrive at about midnight.

The men had good reason to measure this tsunami. Hawai’i had been struck in the past by deadly tsunamis, including ones from Chile in 1837 and 1877 and one from the Aleutian Islands in 1946 that in Hilo alone killed 98 people. Measurements of past tsunamis are commonly used to help identify areas at risk from future tsunamis. Measurements had been made in Hawaii of Aleutian tsunamis, but little was known about the heights of tsunamis from Chile.

In Hilo, Mr. Eaton and his companions stopped to clear their plans with the police and then drove to the Wailuku River Bridge, on the shore of Hilo Bay. They knew that the 1946 Aleutian tsunami had destroyed the bridge there. The men set up an observation post on the new bridge and began measuring the water level beneath it. Just in case, they also planned their own evacuation route, a short sprint to high ground.

Just after midnight, the water under the bridge rose to 4 feet above normal-the first wave of the tsunami had arrived. At 12:46 a.m., the second wave washed under the bridge at a level 9 feet above normal. By 1:00 a.m., the water beneath the bridge had dropped to 7 feet below normal. Mr. Eaton recalls that they then heard an ominous noise, a faint rumble like a distant train, that came from the darkness far out in Hilo Bay. Two minutes later, they began to see the source of the noise, a pale wall of tumbling water, caught in the dim lights of Hilo. The wave grew in height as it moved steadily toward the city, and the noise became deafening.

By 1:04 a.m., the men on the bridge realized that they should run the few hundred feet to high ground. Turning around, they watched the 20-foot-high, nearly vertical front of the wave hit the bridge, and water splashed high into the air. After this wave had passed and they thought it was safe, Mr. Eaton and his companions returned to the bridge and continued to record the water level during several more waves of the tsunami.

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