Saving lives with geohazard maps

THE deadly landslides that recently hit Itogon in Benguet and Naga City in Cebu ought to put into focus the need to heed warnings in geohazard maps that indicate areas prone to landslides, floods, ground subsidence, sinkholes, and other geological dangers to life and property.

For about a decade already, geohazard maps have been produced by the Mines and Geosciences Bureau (MGB) under the Department of Environment and Natural Resources with its implementation of the National Geohazard Assessment and Mapping Program for use by local government units and the general public.

The need for geohazard mapping became more pressing after a massive landslide killed over 1,200 people in Guinsaugon village in Saint Bernard, Southern Leyte, on February 11, 2006. A whole section of a mountain overlooking the village collapsed, causing an avalanche of 1.2 billion cubic meters of mud, rocks, and boulders cascading about three kilometers.

An MGB scientist said the Guinsaugon disaster was really waiting to happen and that “no amount of tree planting could have prevented it.” It was explained that rocks which made up the mountain “were shattered when the Philippine Fault — which runs from Luzon to Mindanao — cut across Leyte Island around five million years ago. This made the rocks prone to weathering, erosion, and alteration. Movements in the fault zone also caused the rocks to continuously grind against each other, pulverizing them in the process.”

With nothing to stop the mountain from collapsing, the best that could be done was to keep people away from the mountain, and geohazard mapping could have pinpointed the danger areas that had to be kept off limits.

The MGB reported that it has already completed the 1:50,000-scale assessment and mapping of 1,640 cities and municipalities nationwide in 2010. In 2011, work was started on geohazard maps on the 1:10,000 scale which was completed and made available in early 2015. It contained more detail and is more accurate and specific compared to the earlier 1:50,000 scale.

In its website, the MGB has identified the top ten provinces highly susceptible to landslides: Marinduque, Rizal, Cebu, La Union, Southern Leyte, Benguet, Nueva Viscaya, Batangas, Mountain Province, and Romblon. But with many precious lives lost in the landslides in Benguet and Cebu believed triggered by the rains spawned by Typhoon Ompong, it is obvious that geohazard warnings were not heeded or efforts to lessen risks were insufficient.

How come warnings of danger and calls for evacuation are ignored? Some say it is because of the nature of geohazards. “We can tell where a particular hazard could happen, but we cannot tell when it will happen,” explained a MGB geologist. Indeed, unlike an approaching typhoon or a restive volcano, a landslide can strike like a thief in the night.

It is therefore imperative upon LGUs to ensure that people benefit from geohazard maps that have been already made available, including those accessible for free online, and that warnings are heeded even if forced evacuation has to be done.

DILG Central Office Disaster Information Coordinating Center Chief Edgar Allan Tabell explained that in the absence of a national law on forced evacuation, it is up to the LGUs to undertake forced evacuations in their areas. “There is enough authority for mayors to conduct forced evacuation under the general welfare clause of the Local Government Code. So even in the absence of a specific law, there is legal authority for the mayor to implement forced evacuation if the conditions so warrant.”

Tabell, who was a studio guest last Sunday in my DZMM teleradyo program Sagot Ko ‘Yan (8 to 9 a.m. Sundays), said that a disaster preparedness audit showed a 78 percent compliance by LGUs on directives to “use the information, findings and recommendations provided along with the geo-hazard maps to enhance disaster risk reduction efforts.”

He also said that local officials are also given training in the use of the geohazard maps that provide lifesaving information. Using the maps, LGUs can do a lot to reduce risks to life and property. They could limit activities, like mining and quarrying, which might trigger the hazard. They could also divert development from high-risk areas, or push for retrofitting and other engineering responses to strengthen structures located near quake faults.

Utilizing the benefits of geohazard maps would indeed go a long way in saving lives in this country prone to many disasters. Email: