On the tsunami trail

Prepared? The world certainly wasn't when the tsunami struck Asian coastlines on December 26, 2004 after a massive 9.2 magnitude earthquake with its epicenter off the coast of Sumatra.

Monster waves as tall as 120 feet lashed the coastlines of 10 countries in the Indian Ocean. The large-scale death and destruction that followed (the official death toll is 2,83,106) left many wondering what exactly caused a tsunami of this scale? The eight-minute earthquakes released energy equivalent to 62,000 Hiroshima bombs.

To predict and be prepared for the next tsunami, Discovery Channel funded an expedition of top scientists from around the world in May 2005 to explore the ocean-bed of the Asian tsunami and understand what caused it.

For a tsunami of a similar scale is a possibility on the North-West American coastline where a major fault line exists under the ocean-bed. Also, the Great Sumatra earthquake ruptured only 750 miles of the Indian Ocean fault line, a vast chain of undersea mountains that runs for 1,600 miles. The other half could break any time.

"There were two theories on the cause of the Asian tsunami and the formation of the giant waves "" the high-magnitude earthquake with the epicentre on the sea-bed, or the landslides caused by the earthquake on the sea mountain ranges," says Dr Baban Ingole, a marine biologist with the National Institute of Oceanography (CSIR), Goa and the only Indian (and Asian) scientist on board the expedition ship, The Performer.

"We wanted to pin-point between the earthquake and giant underwater landslides," he adds.

The international team of 27 scientists, including seismologists, geophysicists, biologists, sea-bed visualisation experts and tsunami modellers had 17 days in hand to uncover the cause of the Asian tsunami and provide data for upcoming tsunami-predicting models.

As the Asian tsunami hit the paradise-like island of Phi-Phi on December 26, 2004, the recording to the destructive waves by a tourist are the first few shots of a programme titled Unstoppable Waves on Discovery Channel, to be aired on December 25, 2005, giving a day-by-day account of the expedition ship and how it unravelled the cause of the tsunami.

As the expedition team on The Performer dealt with technical hitches, Dr Ingole studied the condition of the marine life on the ocean-bed to assess whether any recent activity had disturbed the delicate balance of life deep down.

"Micro-organisms having a short life span live on the top 10 centimeters of the ocean-bed. Three kilometres deep below ocean-level with no sunlight, they feed on the fickle material of bigger organisms. Attached to the fine mud sea-bed, any disturbance caused and the micro-organisms will be uprooted or broken," says Dr Ingole.

Aided with real-time sampling and photography, the expedition team assessed conditions of the ocean floor. With some misleading findings, they accidentally hit on the right evidence, ready to be shared with the world exactly a year later since the catastrophe.

The tectonic plate under the Indian Ocean for millions of years has been moving east, pushing the Asian plate travelling west.

"About 200 years ago the edges of these plates locked together like a zip but continued to push each other," explains Dr Ingole. On December 26, 2004, these plates reached their stress limits and unzipped. The result was the 9.2 magnitude earthquake.

As the expedition team's ROV searched and captured images of the ocean floor, a vertical wall, like a cliff near the fault line, was seen. "The rupture of the tectonic plates along the fault line lifted the western side of the entire underwater mountain chain by 10 feet on an average, and as high as 40 feet in some places," says Dr Ingole.

Explaining further, he says, "When the ocean-floor was lifted up, three kilometres of water above it was also lifted, causing the formation of giant waves that were only 10 feet high but hundred miles from front to back. Nearing land and entering shallow water, the waves travelling at 500 mph slowed but the rear end of the wave caught up, compressing the wave into a huge vertical wall of water and crashing on the coastlines."

The new data collected by the expedition team is being fed into its tsunami-predicting model, which can now predict the height and speed of tsunamis that could strike in other high-risk areas around the world.

"The Indian government is also gearing up its tsunami-predicting model in a big way," says Dr Ingole.

With the mystery of the havoc-creating Asian tsunami uncovered, and no means to prevent, but only predict, its unstoppable waves, "Being prepared becomes very important," warns Dr Ingole.