MIT boffins devise tool for determining landslide risk in tropics

Engineers at the Massachusetts Institute of Technology (MIT) have devised a simple yet effective system for determining an areas landslide risk. They have said the tool could help planners improve building codes in mountainous and tropical regions frequently hit by typhoons.

Washington, June 27 : Engineers at the Massachusetts Institute of Technology (MIT) have devised a simple yet effective system for determining an area's landslide risk. They have said the tool could help planners improve building codes in mountainous and tropical regions frequently hit by typhoons.

Devised originally for Baguio City, Philippines--a city that averages five typhoons annually and holds the world record for most precipitation received in a 24-hour period (46 inches on July 14-15, 1911)--the risk rating system relies on data commonly available in developing countries.

Artessa Saldivar-Sali, a Filipino who developed the system as part of her master's degree thesis work, and Herbert Einstein, a professor in the MIT Department of Civil and Environmental Engineering, used information about the history of landslides, the type of bedrock underlying a slope, the inclination of the slope and the type of vegetation growth to determine an area's hazard rating.

To these, they added land use and population density to determine the overall risk rating.

To prepare their hazard ratings, the researchers mapped the seven types of underlying bedrock in the area, overlaid with data on slope inclination and vegetation growth.

According to Saldivar-Sali, some of their findings are a bit counterintuitive, as for instance, steeper slopes don't necessarily indicate greater landslide risk.

"The system could be applied directly to any country with similar topography, geology and climate, which would be much of Southeast Asia," said Prof. Einstein.

In her thesis, Saldivar-Sali reported some 65 recorded landslides near Baguio City between 1991 and 2004.

Findings revealed that the landslide hazard didn't "follow any kind of predictable pattern".

"The conclusion we reached is that the landslide hazard is determined by a combination of two factors: the underlying bedrock and the slope," said Saldivar-Sali.

They found that landslides were less common in areas with limestone bedrock, even though they might be relatively steep.

"Limestone is a very hard rock that forms steep slopes naturally. So the steep slope is the stable condition for this rock," she said.

"The fact that the Baguio area has constant, heavy rainfall makes it very susceptible to landslides, which occur frequently. Although everybody knows that, nobody has ever put a system in place to determine where this risk or hazard is higher," she added.

She further said that while roughly half of the 50-square-kilometer area rested on bedrock from the Pliocene Baguio Formation, only 5.7 percent of landslides occurred in these areas, and more than half of those took place on moderate slopes.

"Broadleaf trees provided the least amount of protection on this type of bedrock. But in general, a mix of broadleaf trees or bushes and scrub provided the most protection," she said.

"The highest incidence of landslides in the area (14.3 percent) occurs on bedrock from the oldest geologic era represented, the Cretaceous Pugo Formation of volcanic rock, which accounts for only 1.4 square kilometres of the total area," she said.

ANI