Tsunamis a threat to Pacific Northwest.

• Position: Geology - Brief Article

On the 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 seconds, waves up to 45 feet high surged over the tropical lagoons, battered people with debris, swept them inland, and killed more than 2,200.

That was a tsunami, the most powerful wave in the world. Usually triggered by earthquakes, tsunamis bear little resemblance to regular 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. When they approach land, however--depending on their size, speed, and the underwater topography--they can mount enormous, destructive, and repeated waves. With its combination of a vast ocean and the frequent seismic...