As aid workers rush to provide for the survivors of the recent Indian Ocean tsunami, the damage to the local environment is still being assessed. The ecological disaster may intensify the crisis faced by communities who are dependent on the sea and local agriculture. David Sugarman, a biologist and researcher, spoke this Saturday at the Ontario Science Centre on the physics of the tsunami and the possible future impacts of this environmental disaster.
Not only did the tsunami destroy the local infrastructure and kill hundreds of thousands of people, it may also have permanently damaged the local environment. Many fields and rice paddies near to the coast have been destroyed or are now contaminated with salt water, as are local wells. While sewage in the wells can be cleaned, salt-water contamination of agricultural fields may not be so easily repaired. As well, coral reefs off the coast of Sumatra, already under stress, may have been further damaged by silt. This damage may harm fish stocks, a staple food for many in the area.
Part of the reason for the massive scale of this disaster stems from the high population density in coastal regions. These locations are obviously more susceptible to tsunamis. Sugarman explained why people live in such dangerous locations. “Rice is a good source of energy, but everybody needs protein and where are you going to get your protein in those areas? You throw your net in the water and pull out fish for your family,” said Sugarman. “It’s like living next to the grocery store.”
The tsunami was caused by the largest earthquake in 40 years. When a 1,200km long section of the Indian tectonic plate slipped beneath the Burma plate, the displacement of water caused huge waves to form. On the open ocean the height of the crest was low, but the distances between crests was huge. Boaters far from shore would only have felt something similar to a typical ocean swell as the waves passed, at 900 km/hr. When a wave hit the shallow coastal waters it slowed and the height of the wave grew. This caused the initial wall of water experienced on the beaches of Indonesia, Sri Lanka, India, and Thailand; but in low-elevation areas such as Banda Aceh the water continued to rush inland, wiping out entire villages.
The slipping of the Indian tectonic plate beneath the Burma plate is part of a process called subduction. The boundary between the two plates stretches from Myanmar in the north to the west coast of Sumatra, where it meets the Sunda trench at the border of the Australian and Eurasian plates. Subduction-type tectonic plate collisions are the most likely to yield large earthquakes and hence create tsunamis. Other subduction boundaries exist along the west coast of South America and off Alaska.
However, tsunamis in the Indian Ocean are rare. Eighty per cent of all tsunamis occur in the Pacific, 10 per cent in the Atlantic, and the remaining occur elsewhere. Previous tsunamis of this scale hit Portugual in 1755, the Indian Ocean in 1883 after an eruption of the Krakatoa volcano, and, more recently, Chile in 1960 and Alaska in 1964 after the “Good Friday” earthquake. Sugarman was hesitant to compare this tsunami to previous historic examples, saying only: “My guess is that this is not atypical.” Sugarman noted that this has been the most-documented geological event ever.
