In a report to Environment and Natural Resources Secretary Michael Defensor, the Region 7 office of the Mines and Geosciences Bureau (MGB) said the landslides in Barangay Mayana are expected to continue during the rainy season because rainwater would seep through the porous and fractured limestone deposits, causing the underlying deposits to soften, resulting in landslides.
Roger de Dios, acting MGB regional director, said the toe of the landslides has already reached the Tibug Daku Creek, which drains into the Alinawan River.
A joint investigation conducted by the MGB and University of the Philippines-National Institute of Geological Sciences showed that cracks having a maximum displacement of about 11.5 centimeters were observed at the cemetery area of Barangay Mayana, and the total length of the landslide debris has already reached 1.75 kilometers.
The team added that the national road connecting the towns of Jagna and Sierra Bullones is already impassable to motorists because the landslide debris has covered the road.
Antonio Apostol, chief of the MGB’s Land and Geological Survey Division, told The STAR that the continuous earth movement has adversely affected 70 hectares of agricultural lands.
"We are expecting the 70 hectares already affected to expand due to the rains. The soil remains unstable as continuous soil movements are being noted by the team of experts in the area," he said.
Apostol said the town’s increasing population and development caused the soil in Barangay Mayana to become unstable, among other factors.
For many years prior to the town’s booming, Apostol said no such landslides had occurred.
"People have managed to encroach into the mountainous portion, thus destabilizing the slopes of the mountain. The geological composition of the land in the area is mostly lime," he said.
Apostol said Barangay Mayana’s location near a river also portends looming danger since continuous soil movements could possibly lead to the formation of an artificial dam.
Because of this, he said they are now closely watching the situation so as to alert the residents downstream of Jagna and Dueno towns against any impending disasters.
"We cannot force everyone to evacuate since it is also not that easy to find another place to relocate the people. So we intend to concentrate on the downstream (area) so they could be warned early," Apostol said.