Cascadia's Fault - Jerry Thompson [130]
Titov’s math turned out to be pretty much bang on. When they ran the simulation it revealed things about wave behavior that no one had seen before. It showed, for example, that a tsunami could bounce off one island and hit the back side of another with even greater force.
Titov, standing in front of a floor-to-ceiling map of the world’s oceans spread across the wall of a large conference room wall at PMEL, pointed to Sri Lanka, thousands of miles northwest of Sumatra. “So it came to Sri Lanka and hit hard.” Titov’s finger traced the leading edge of the tsunami to the southeastern beaches of Sri Lanka, where the first pulses crashed ashore with deadly force.
“On the back side, it was protected,” Titov continued, pointing to the lee side of the island between India and Sri Lanka. “It was sort of shielded from the first wave. But then the wave bounced off the Maldives,” his finger followed the path across to the next neighboring island chain, southwest of Sri Lanka. “It reflected from here [the Maldives] and then hit the backside of Sri Lanka with much stronger waves.”
And there was stunning home video footage to prove the point. A mound of water slammed against the seawall at a luxury resort, shot a geyser of white spume into the sky, and then surged across the pool deck, sweeping away everything in its path. On the back side of Sri Lanka.
Titov’s model also illustrated how the train of monstrous swells would turn corners around continents and eventually hit beaches on the opposite side of the planet. Big mountain ranges at the bottom of the Indian Ocean steered the on-rushing tsunami in new directions, according to Titov. He shifted his hand to the southern Indian Ocean and pointed to an undersea ridge. “You don’t see them on the surface, but the wave does see them.”
In a computer lab down the hall, he showed me how his model had replicated the motion. As the tsunami approached a ridge of very large undersea mountains, the wave began to bend and change trajectory. “The wave feels the shallow water and it slows down over this ridge,” Titov explained. The tsunami scraped along the edge of the mountain range and friction slowed the left side of the wave down. The right side—still in deep water—continued to move at a higher speed. The difference in speeds from one edge to the other caused the wave to turn. In essence the undersea mountains became a wave guide, warping the deadly swells in a new direction.
But only up to a point. “If the mountain range turns sharply,” Titov continued, “the wave would not turn. It will leave the guide.” That’s exactly what happened at the bottom of Africa. The tsunami veered off a mid-ocean ridge and rebounded like an eight ball to the corner pocket—around the tip of the African continent, crossing from the Indian Ocean into the South Atlantic. An example of “very interesting physics,” Titov said, with barely controlled enthusiasm.
Roaring past the Cape of Good Hope, the sea monster moved up and across the Atlantic, coming ashore and leaving footprints on the beaches of South America. “A tsunami generated in the Indian Ocean—in Sumatra, half the world around—turned out to be a meter in Brazil,” Bernard pointed out, with a shrug of amazement. “Fortunately it was at low tide, so it didn’t do any damage.” Sumatra’s biggest wave even showed up on tide gauges as far away as Halifax, Nova Scotia.
The computer model predicted that the tsunami would circle the entire planet, and physical data from beaches and harbors around the globe confirmed the prediction. Then a bit of luck added another layer of confirmation. Two weeks after the tsunami, scientists at NASA notified Eddie Bernard and Vasily Titov that one of their satellites just happened to be overhead precisely when the tsunami was crossing the Indian Ocean.
“This tsunami was big enough in the open ocean—about forty centimeters—that [the satellite] actually detected it,” said Bernard. Forty centimeters (15 inches) didn’t sound