OREGON STATE UNIVERSITY

Dangerous tsunamis threat to Pacific Northwest

02/06/2001

CORVALLIS, Ore. - On the warm Friday evening of July 17, 1998, villagers on the northern coast of Papua New Guinea were finishing a quiet day when a magnitude 7.1 earthquake suddenly shook the area and the offshore ocean bottom lurched upwards.

At first the sea receded. Then within 15 minutes, waves up to 45 feet high surged over the tropical lagoons, battered people with debris, swept them inland and killed more than 2,200 villagers.

That was a tsunami, the most powerful wave in the world. Usually triggered by earthquakes, they bear little resemblance to the usual ocean waves which are a mere ripple by comparison, and have nothing to do with tides, even though they are often inaccurately referred to as tidal waves. They can be huge and travel at enormous speeds of more than 400 miles per hour, fast enough to keep pace with a jet airliner.

Tsunamis are not dangerous in deep water, where they often pass unnoticed. But when they approach land, depending on their size, speed and the underwater topography, they can mount enormous, destructive and repeated waves.

Researchers at Oregon State University and from around the world will use a new tsunami wave basin research facility to gain a better understanding of the behavior of these deadly waves.

With its combination of a vast ocean and the frequent seismic activity of the "Ring of Fire," the Pacific Rim is particularly vulnerable to tsunamis. Twelve damaging tsunamis have struck Hawaii since 1895, including a killer wave in 1946 that originated near Alaska and killed 159 people in the islands.

It's now clear that the Pacific Northwest is eminently vulnerable to the destruction of a tsunami, most likely due to earthquake activity on the Cascadia subduction zone. Studies have identified sand and gravel deposits that scientists believe were carried far inland from the coast by past tsunamis on this subduction zone.

In 1992, the Cape Mendocino earthquake caused a tsunami that may just be a mild, sneak preview of more destructive waves in the region's future.