Negros warned of more landslides, floods; faults intersect twin lakes

DUMAGUETE CITY—The presence of twin lakes and four intersecting geologic faults has increased the possibility that earthquake-triggered landslides and flash floods may occur in the city and in four towns of Negros Oriental, former Environment Secretary Angel Alcala said.

In an e-mailed statement titled “Unsolicited advice for Gov. Roel Degamo,” Alcala said the local government units (LGUs) of Dumaguete, Valencia, Sibulan, San Jose and Amlan should be on alert on the occurrence of the natural disasters, but he added that their probability could not be known.

He cited what happened in Mount Parker in South Cotabato on Sept. 6, 1995, when a wall of its crater lake, Maughan, caved in and spilled about 30 million cubic meters of water. The flash flood killed over 100 people.

Several faults are found near Maughan and the volcano itself, said Alcala, a marine biologist and recipient of the Ramon Magsaysay Award for public service in 1992. He served as secretary of the Department of Environment and Natural Resources (DENR) during the administration of President Fidel V. Ramos from 1992 to 1995.

In Negros Oriental, a normal fault separates Lakes Balinsasayao and Danao in Sibulan and another fault, the Amlan, is about 1,400 meters west of Danao, he said.

He noted the presence of four geologic faults that intersect and in the southern edge of Lake Danao, whose water level is lower than that of Balinsasayao.

“Movements along these intersecting faults near or within the two lakes during an earthquake could trigger a rupture on the lake walls, allowing water to seep and eventually result in the collapse of these walls. Should this happen, flashflooding and massive mass movement or landslides would occur,” Alcala said.

Although a reptile specialist, Alcala had undertaken studies of the twin lakes years ago when he headed the Research and Development Office of Silliman University here. He compares notes with his two sons who are geologists.

At present, he is a trustee of Silliman and a director of Centro Escolar University.

Alcala urged Governor Degamo and the mayors of the three towns to request the Philippine Institute of Volcanology and Seismology (Phivolcs) and the Mines and Geosciences Bureau (MGB) to inspect the Talinis-Lake Balinsasayao area to determine any effects from the recent earthquake and to recommend appropriate actions for the LGUs.

Alcala also asked the agencies to make the survey report public.

Last week, Phivolcs Director Renato Solidum Jr. and MGB Director Leo Jasareno gave a lecture to journalists and government officials in Dumaguete on the science behind earthquakes and tsunamis.

They called on all local government officials to lead in the mapping of geological hazards in their barangays and municipalities, and prevent people from building houses near the faults or in places exposed to floods and tsunamis.