“Other villagers were not so lucky,” she continued. Swenson displayed a quick series of slides of the station where the tsunami had struck the train. The first revealed the village prior to the earthquake. People were standing about beside the rust-red cars. They were smiling. They were waving. The small village of Telwatte was clearly visible nearby. It was a bright and sunny day.
The next photograph was taken from exactly the same spot, the same angle even, although — at first — it was difficult to tell. In this slide, the station of Telwatte had been obliterated. Little remained. And the railroad cars lay twisted and scattered about in great heaps.
“Like Vidu,” she continued, “some of the passengers and local villagers were swept across the jungle. Many were battered to death by debris. The trees were bejeweled with sheets of corrugated iron.” A series of three slides displayed the coastline. Trees were flattened, as if by a nuclear explosion.
“At least sixty people lost limbs to gangrene, or to the feral dogs and crocodiles that descended on the helpless victims. It was difficult to arrive at an accurate death count, but at least one thousand of the train passengers were killed. Less than one hundred survived. A total of six waves struck the train and village — one, as high as twenty feet. Of the few local inhabitants who knew about tsunamis, most found themselves incapable of fleeing from the coast. There was simply no place to go.”
The lights in the auditorium grew brighter. Swenson could see the faces of the students clearly now. They looked horrified. Good, she thought. Most scribbled furiously in their notebooks. The scraping of pencils and pens, the chatter of keyboards: These were the most satisfying of sounds, for they marked the capture of her audience. Her tactics were working. While she hated to exploit the suffering of Vidu and the other villagers whom she had come to know and love, she realized it was necessary. She needed these students to feel if they were going to respond. Her discipline was desperate for additional researchers, for scientists who might one day prevent another tragedy like this one from ever happening again.
A spotlight shone upon her head and Swenson took a breath. “To understand tsunamis,” she continued, “you must first distinguish them from wind-generated waves or tides. Breezes blowing across the ocean crinkle the surface into relatively short waves that create currents restricted to a rather shallow layer. While gales, hurricanes and typhoons can whip up waves of thirty meters or even higher in the open ocean, they do not move deep water. Tsunamis are never generated by the gravitational forces of the sun or moon. They’re produced by earthquakes — such as in Sumatra — or, much less frequently, by volcanic eruptions, landslides, or the impact of meteors or comets.”
She moved from the lectern and a QuickTime sequence filled the movie screen behind her. Blue animated waves began to heave, replaced by a 3-D cutaway of the water column down to the ocean floor. It was impressive animation, colorful and distracting. But most of the audience remained focused on Swenson.
Dressed in an off-white midi lab coat over a dark plaid skirt, she had spent a long time pinning up her hair into a kind of frumpy bun to prevent it from shimmering distractedly. She wore a pair of tortoise-shell glasses. She wore no makeup and no jewelry. But all of these well-planned counter-measures only seemed to make her more alluring.
To be intelligent and to look like this? It was a fucking outrage. This is what they were thinking. No one deserved such fortune, no matter what their previous life. Most people believed that if you were good-looking and smart, you must have some hidden failing, deep inside. And even if you didn’t, not really, it meant they had to look for one, which was — in and of itself — a bit of a nuisance. And they always discovered one, even if they had to make it up. It was all about finding balance, some kind of order in their world when confronted with something that was clearly out of sync, unnatural, perhaps a genetic aberration, most certainly a statistical anomaly. Swenson saw the same thing in nature all the time. To be so fortunate meant you were already doomed. What were discrete blessings, individual gifts, together proved too much for most. Sometimes her face and figure helped; usually they were just annoying distractions. As her mother used to say, “We each carry our own cross.” Research was a great place to hide.
“Tsunamis,” she continued, “can attain speeds of up to 700 kilometers per hour in the central reaches of the oceans. But, despite their speed, tsunamis are generally not particularly dangerous in deep water. Most waves are less than a few meters high, although their lengths can exceed hundreds of kilometers.”
Another screen popped to life, displaying a view of the Pacific Ocean from space. This morphed into an animation, charting the movement of the wave below. Then the POV collapsed, as if the satellite were falling from the sky, plummeting to the earth like Icarus, only to slow and hover a few feet from the downward side of the tsunami, revealing its low roll.
“This creates a sea-surface slope so gentle that tsunamis usually pass unnoticed in deep water. Indeed,” she said, “the Japanese word tsu-nami translates literally as ‘harbor wave,’ perhaps because a tsunami can travel undetected across oceans, then rise up unexpectedly within shallow coastal waters.”
The first screen glowed with a map of the Indian Ocean. “Regardless of their origin,” she said, “tsunamis evolve through three overlapping but quite separate physical processes: generation, by any force that disturbs the water column; propagation, from deeper water near the source, to shallow coastal areas; and, finally, inundation, as the waves sweep up onto dry land. Of these, the propagation phase is the best understood. Generation and inundation are much more difficult to model.
“Generation,” she explained, “is the process through which a seafloor disturbance — such as a movement along a fault — reshapes the surface of the sea. When nearly all of an earthquake's energy is released in a thrust motion, as in the Sumatra quake, a large tsunami is generated. In contrast, strike-slip earthquakes, such as the one in San Francisco in 1906, are not efficient tsunami generators.
“The location of the 2004 Sumatra centroid,” she continued, “defined as the location of the center of energy release, was near the Sunda trench, in relatively deep water. This generally results in an initial tsunami with larger potential energy than a tsunami whose centroid is closer to shore. Researchers use an idealized model of a quake since only the orientation of the assumed fault plane and the quake’s location, magnitude and depth can be interpreted from seismic data. Other parameters, including the amount of slip, and its length and width, must be estimated. That’s why initial simulations frequently underestimate inundation, sometimes by a factor of five or ten.”
The second screen sparkled with numbers, spinning formulae and colorful input fields; the third with animated models of tsunamis based on the various data feeds.
“The second process,” she continued, “propagation, transports seismic energy away from the earthquake through undulations of the water. Waves slow down as they travel over decreasing water depth, so that they eventually overtake one another, narrowing the distance between them in a process called shoaling.”
All three screens began to display clips of different tsunami landfalls, crashing through villages and towns, in color and black-and-white, rushing up rivers and canals, sweeping the world away.
“Inundation,” she concluded, “the third and final stage, is the most difficult to model. The wave height is now so large that initial linear theory fails to describe the complicated interaction between the water and the shoreline. Vertical run-up can reach tens of meters, but it typically takes only two to three meters to cause significant damage. The Indian Ocean tsunami was responsible for killing more than two hundred thousand people worldwide — from Sumatra to Somalia — although some speculate the death toll may climb higher, to as many as a quarter of a million souls.”