Killer landslide in Naga ‘unique’ – MGB

By Rosalie O. Abatayo and Zena V. Magto |October 22,2018 - 11:17 PM


THE MASSIVE landslide in Naga City was no ordinary phenomenon.

A team of geologists from the Mines and Geosciences Bureau (MGB) in Manila on Monday said the soil in the mountain of Barangay Tinaan, Naga, did not just erode but completely collapsed or sank.

“It was a one-of-a-kind landslide. It was unique,” said MGB chief geologist Liza Manzano in a press conference at the Naga City Hall on Monday.

Four factors, she said, contributed to the phenomenon— soil characteristic, previous earthquakes, climate and human activities.

While the landslide was mostly caused by environmental factors, Manzano said the quarry operations in the mountains of Barangay Tinaan also contributed to the tragedy.

“Any activity that you do to change the landscape of the mountain, including quarry operations, is contributory to the incident,” she said.

In an interview after the press conference, Manzano clarified a separate team from MGB that conducted another inspection ruled that Apo Land and Quarry Corporation (ALQC), which operates in Barangay Tinaan, did not commit any malpractice.

Environment Secretary Roy Cimatu, who was present during the presentation of the MGB in Naga, said he still would not lift the ban on the quarry activities of ALQC while the investigation continued.

“No lifting of ban (for now) because it is still dangerous for quarrying operations,” he said in a interview. Cimatu did not elaborate.

According to Manzano, the 7.2 magnitude earthquake that rocked Bohol and Cebu in 2013 greatly affected the stability of the soil in the mountain of Barangay Tinaan.

“The shift and ponding of subterranean flow may have caused the build up of hydrostatic pressure that leads to the landslide,” Manzano’s report read.

Hydrostatic pressure is the force exerted by a fluid, water in this instance, due to gravity.

Manzano said the highly porous and water solubility characteristic of limestone, which largely composes Naga City’s soils, also contributed to the vastness of the slide.

The MGB report also included a new delineation map which determined three zones in the periphery of the landslide area: danger zone, no permanent habitation zone and regulated zone.

The danger zone, which includes the immediate surrounding of the ground zero, is strictly off limits to settlers.

The no permanent habitation zone, on the other hand, is outside the immediate danger zone. It can be converted into an eco-park but cannot be used for urban settlements.

Regulated zones are those located several meters away from the ground zero.

Manzano said further studies have to be made to find out whether or not residents in the area will be allowed to return home.

A geotagging activity will be conducted on Wednesday by personnel of the Department of Environment and Natural Resources and the Naga City government to determine the houses that need to be relocated.

Naga City Mayor Kristine Vanessa Chiong said they will present the relocation plan for the affected families once they are finished with the final geotagging activity.

“I am ready. I already submitted the financial humanitarian assistance scheme and options once the final list of affected families will be available,” she said.

Chiong said they hope to come up with the final list on Thursday, October 25.

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