BAGUIO CITY - Four houses crumpled and fell into a gaping hole that gave way beneath a community in Benguet's mining town of Itogon on Thursday, a day after Typhoon "Lando" (international name: Koppu) left the country.
Results of initial geological investigation, however, discounted speculation that the hole was part of an old tunnel once used for a mining operation there.
Fay Apil, a geologist and Cordillera director of the Mines and Geosciences Bureau (MGB), said the houses were dragged down the side of a hill and swallowed by the hole in Virac village.
Itogon Mayor Victorio Palangdan said the families living in the collapsed houses managed to flee after they felt their houses were shaking.
He said the hole gave way gradually. The first evidence of subsidence was detected by residents at 10 a.m. on Thursday. The hole began to grow wider in the afternoon.
The displaced families, as well as 32 other people, were relocated to Virac Elementary School.
Apil said at least 100 families were evacuated from the area. "The police worked quickly to clear these houses," she said, after she and a team inspected the ground subsidence and helped identify the endangered houses.
Palangdan said engineers of the mining company came to check on the ground movement on Saturday. "But they did not show us any plans of action yet," he said.
Apil said geologists and the mining company's engineers inspected two underground mine structures which run beneath the subsidence area in Virac.
She said the old "Vegas" tunnel was the closest, having been part of the company's tourist-drawing mine tours. But the team found no evidence of collapse there when it visited the tunnel.
Apil said the team also inspected the old "Diversion Tunnel No. 1," which is being used to discharge water. On the surface, the length of this diversion channel is equivalent to an 80-meter stretch from the road.
But the team, accompanied by Virac village chief Noel Bilibli, checked the tunnel outlet and concluded that the volume of discharge was unhampered and the quality of water was clear, she said.
The diversion tunnel had not been compromised, she said, adding that the team and local officials would enter the tunnel on Oct. 27.
She said the MGB is working on another theory: The void underneath might be the result of operations of illegal small-scale miners. She did not elaborate.
Itogon is home to some of the country's first mining companies, most of which were established when the country was ruled by the American colonial government.