ESASHI, Japan -- They can travel as fast as jet planes. They can carry off entire houses. They can inundate coastal communities with violent flooding. Some English speakers call them tidal waves, but they have nothing to do with tides; much of the world recognizes them by their Japanese name, tsunami.
Huge tsunamis inundated northern Japan Monday night, minutes after a powerful earthquake struck the Sea of Japan west of the northern island of Hokkaido. A tsunami contributed heavily to damage along the coast and to the virtual demolition of the Aonae district on Okushiri, a small island known for fishing and resorts.
People were swept away by huge waves and drowned. Cars were flushed into the sea. Ships were thrown onto land where they crashed into buildings. And hundreds of houses were destroyed in a torrent of water. One of the most striking television images of the quake was that of what looked to be an entire house floating out to sea, its roof protruding above the water.
Many things contributed to the damage in the quake, which measured 7.8 on the Richter Scale. There was the shaking, the landslides that ruined roads and buried a hotel, and fires, probably caused by the explosion of ruptured gas lines. But perhaps the most spectacular phenomenon was the tsunami.
While Japan, perhaps the world's most earthquake-prone country, has learned how to build structures to withstand earthquakes, it apparently has not yet been able to fully cope with tsunamis.
"Even wooden houses in Japan are built strong enough to withstand the shaking of an earthquake," said Nobuo Shuto, a professor of tsunami engineering at Tohoku University in Sendai.
Japan has a warning system for tsunamis, but on Monday night the waves reached Okushiri about the same time as the warning, five minutes after the earthquake.
"Under this kind of situation, maybe there is little you can do," Dr. Shuto said. "The only way to save human lives is to evacuate immediately, even without a warning."
Dr. Shuto estimated that the wave that struck Okushiri ranged from 10 to 16 feet high, but noted that he said he had not completed his calculations. A researcher for the Meteorological Agency estimated, based on a survey of the site, that the waves were as high as 35 feet.
The tsunami's speed depends on the depth of the water above the displaced sea bed. In the case of the tsunami Monday, where the water was about 6,000 feet deep, the wave travels at 300 mph.
Japan began constructing defenses against tsunamis after it was hit by what Dr. Shuto said were the strongest waves in its recorded history, with some up to 40 feet high. The tsunamis, which struck in 1960, started off the coast of Chile and took 23 hours to cross the Pacific before slamming into Japan.