Tsunami Science: The Calm Before the Wave
Feb 3, 2012; 9:00 AM ET
Where and when will the next tsunami hit?
Indonesia: A U.S. Marine helicopter loaded with food flies over Lampuuk in northern Sumatra on January 4, 2005, nine days after a tsunami killed most of the village's 7,000 residents-and some 230,000 people on coastlines around the Indian Ocean. Many locals believe divine intervention saved the Rahmatullah mosque. ©John Stanmeyer/National Geographic
Jin Sato is the mayor of a town that no longer exists.
Minamisanriku, a quiet fishing port north of Sendai in northeastern Japan, disappeared last March 11. Sato nearly did too. The disaster started at 2:46 p.m., about 80 miles east in the Pacific, along a fault buried deep under the seafloor. A 280-mile-long block of Earth's crust suddenly lurched to the east, parts of it by nearly 80 feet. Sato had just wrapped up a meeting at the town hall. "We were talking about the town's tsunami defenses," he says. Another earthquake had jolted the region two days earlier-a precursor, scientists now realize, to the March 11 temblor, which has turned out to be the largest in Japan's history.
When the ground finally stopped heaving, after five excruciating minutes, Minamisanriku was still mostly intact. But the sea had just begun to heave. Sato and a few dozen others ran next door to the town's three-story disaster-readiness center. Miki Endo, a 24-year-old woman working on the second floor, started broadcasting a warning over the town's loudspeakers: "Please head to higher ground!" Sato and most of his group headed up to the roof. From there they watched the tsunami pour over the town's 18-foot-high seawall. They listened to it crush or sweep away everything in its path. Wood-frame houses snapped; steel girders groaned. Then dark gray water surged over the top of their building. Endo's broadcasts abruptly stopped.
Some 16,000 people died that day, most of them along hundreds of miles of coast in the Tohoku region, and nearly 4,000 are still missing. The tsunami eradicated several towns and villages in Tohoku and left hundreds of thousands homeless. In Minamisanriku the killed or missing number about 900 of 17,700 inhabitants, including Miki Endo, whose body was not found until April 23. Sato survived by climbing a radio antenna on the roof and clinging to it. "I think I was underwater for three or four minutes," he says. "It's hard to say." Many of the 30 or so other people on the roof tried to hang on to the iron railings at its edge. The waves kept coming all night long, and for the first few hours they repeatedly inundated the three-story building. In the morning only ten people remained on the roof.
Japan leads the world in preparing for earthquakes and tsunamis. It has spent billions retrofitting old buildings and equipping new ones with shock absorbers. High seawalls shield many coastal towns, and well-marked tsunami evacuation routes lead to high ground or to tall, strong buildings. On March 11 government seismologists had barely stopped hugging their computer monitors to keep them from crashing to the floor when their first tsunami warning went out.
Together these measures saved many thousands of lives; Miki Endo alone may have saved thousands. The Tohoku earthquake itself-a magnitude 9-did much less damage than it would have in other countries. But between 16,000 and 20,000 died because of the tsunami-a death toll comparable to that caused by an earthquake and tsunami in the same region in 1896.
A fault that runs under Puget Sound could cause a damaging earthquake in Seattle-seen here from a boat floating above the fault-and a tsunami that would strike the waterfront in less than ten minutes. ©John Stanmeyer/National Geographic
Japan's defenses have improved tremendously since then, but its population has tripled. Its coasts are far more crowded. The same is true all over the world, in countries that are much less prepared. In the Indian Ocean, where the deadliest tsunami in history killed nearly 230,000 people in 2004, most of them in Indonesia, a similar disaster has been forecast for sometime within the next 30 years. In the United States, where a tsunami devastated the Pacific Northwest 300 years ago, when it was sparsely inhabited, geologists say another is inevitable. It's likely there will be many Minamisanrikus in the decades ahead.
Sato had survived a big tsunami before. In 1960, when he was eight, a 14-foot wave killed 41 people in Minamisanriku. The seawall was built after that, to a height of 5.5 meters, a little over 18 feet. "We thought we would be safe," Sato says. "Seismologists had told us to prepare for a tsunami that might be five and a half to six meters high. But this one was three times that height." Afterward, in the landscape of debris that had been his town, almost the only thing that remained intact was the seawall.
Indonesia: In March 2005 a second earthquake off Sumatra unleashed only moderate waves-but lowered the land in some coastal areas by three feet, triggering flooding. On Pulau Balai, Rahmaniar, 23, still walks on coral chunks she used to raise her home's floor above the tides. ©John Stanmeyer/National Geographic
Tsunamis strike somewhere in the world almost every year, and giant ones have arguably changed history. Some archaeologists have argued, for instance, that a Mediterranean tsunami struck the north shore of Crete a bit over 3,500 years ago; the disaster, they say, sent Minoan civilization, one of the most sophisticated of the age, into a tailspin, leading it to succumb to Mycenaean Greeks. In 1755, when an earthquake and tsunami killed tens of thousands in Lisbon, the tragedy had a lasting impact on Western thought: It helped demolish the complacent optimism of the day. In Voltaire's novel Candide the blinkered philosopher Pangloss arrives in Lisbon during the catastrophe, persists in arguing that "all is for the best in the best of all possible worlds," and gets hanged for his trouble. Voltaire's withering satire made it a little harder to be Panglossian-to believe that a benevolent God designed an optimal Earth.
In the fifth century B.C. the Greek historian Thucydides was the first person to document the connection between earthquakes and tsunamis. He noticed that the first sign of a tsunami is often the abrupt draining of a harbor, as the sea pulls away from the coast. "Without an earthquake I do not see how such things could happen," he wrote. Actually they can. The Minoan tsunami was triggered by the cataclysmic eruption of Thira, a volcanic island 70 miles north of Crete in the Aegean. And landslides can cause local tsunamis, such as the one that surged 1,700 feet up a hillside in Lituya Bay, Alaska, in 1958 (see photo). All it takes is a large mass of rock moving abruptly in a large mass of water-not necessarily the ocean.
These photos and more on the story can be found in the February 2012 issue of National Geographic magazine.
credit: National Geographic
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