Forecasting Tsunami Threats Through Layers Of Sand And Time

For an ancient dialect to have its own phrase for destructive waves triggered by earthquakes, the people of Tamil Nadu likely experienced tsunamis periodically through the centuries, says Halifax scientist Alan Ruffman.

In other words, the catastrophic Indian Ocean event in December 2004 that killed 230,000 people in a dozen countries – including 15,000 in India – was hardly a one freak occurrence, he says, and people could have been much better prepared for it.

The proof lies in the layers below the Earth’s surface, says Mr. Ruffman, honorary research associate in Dalhousie’s Department of Earth Sciences. What better way to predict the threat of future tsunamis than studying patterns from the past? Coastal sediments provide a potent geological record of recent and ancient tsunamis, he says, adding that the size of the sand particles can provide clues about the actual height of the water column.

He points to a compelling photo of a research colleague at a dig in Thailand, showing four distinct bands of sand. The surface layer was deposited by the 2004 tsunami, and Mr. Ruffman figures the next layer was left by an event dating back 400 to 600 years. “The tsunami that laid that one down was probably about the same size as the one in 2004,” he says.

This kind of research is relatively new. Much more study is required to develop statistics and timelines that can serve as a guide to help people in Southeast Asia better prepare for the next monster wave. And Halifax will be part of that important effort, Mr. Ruffman learned last week. The Shastri Indo-Canadian Institute has awarded a seed grant to help Dalhousie develop a tsunami research partnership with the University of Madras in Chennai, India.

In his funding proposal, Mr. Ruffman envisioned a long-term alliance to generate potentially life-saving new knowledge from research by faculty and students in the two coastal cities, starting with in-depth study of the history of tsunamis in the Bay of Bengal. This will range from detailed geological sediment studies to analysis of southern India’s early writings and folklore, to find human accounts of early tsunamis.

“There are more than 1,500 unanalyzed early documents in the Tamil language that stretch back one to two thousand years,” says Mr. Ruffman.

And if the Tamil Nadu sediments tell a similar story to the layers shown in the striking photo from Thailand, “then our scientific team should be able to put a solid estimate on the return period of such devastating events. This would allow communities and governments to put in place the necessary tsunami warning systems and evacuation procedures for future events,” Mr. Ruffman says.

It could go much further than that, with such proactive steps as restoring mangrove vegetation, to help prevent tsunami erosion along coastlines, and even moving whole villages to safer locations.

“If the understanding of the very real and present tsunami hazard leads to better location of coastal villages, housing and infrastructure, then the financial and human losses during future tsunamis will be greatly reduced. But planners and governments will have to believe that the 2004 tsunami was not a unique event ... and there’s nothing like finding a signature of a historic event to convince the local policy-makers it has occurred before.”

The Shastri funding proposal suggests Dalhousie would host a week-long series of workshops, seminars and social functions, attended by tsunami researchers from Madras, as well as local scholars and members of Halifax’s Indo-Canadian community. The Earth scientists would also use the time to hammer out a plan for their cooperative research program, and explore opportunities for graduate student exchanges between the two universities.

The core research team would include four Madras scholars, six Dalhousie faculty members in Earth Sciences and Oceanography, and the Bedford Institute of Oceanography.

Mr. Ruffman has been researching tsunamis for more than two decades. His main focus thus far has involved historic events in the Atlantic, such as the 1755 Lisbon Tsunami, and the 1929 Grand Banks event that killed 28 people in Newfoundland.

“In 1929 the tsunami surged up to a kilometre and a half inland,” he noted. “Houses were floating out to sea with oil lamps still seen burning in the windows. These events, though rare, do occur in the Atlantic.”

In a recent presentation to the Atlantic Geoscience Society, he also discussed possible connections between climate change and tsunamis—coastal areas with rapid deglaciation can become vulnerable to shifts in the Earth’s crust, triggering seismic activity that could launch tsunamis.

“It’s not a hazard that will happen tomorrow, or often,” says Dr. Ruffman. But once tsunami researchers get a handle on the Bay of Bengal, there’s plenty more work to be done in Greenland, Iceland and Labrador, he says.