Gov’t experts find rupture in old mine diversion tunnel in Benguet

THIS is the “mysterious” hole that opened up after a cave-in at the community of Virac in Benguet’s mining town of Itogon. It has swallowed six houses so far since Oct. 22. RICHARD BALONGLONG/INQUIRER NORTHERN LUZON

BAGUIO CITY—Government geologists and mine engineers have found a rupture in one of the diversion tunnels of an old mine in Itogon, Benguet province, which runs 80 meters beneath houses that are slowly being swallowed by a huge hole.

Six houses fell into this pit from Oct. 22 to 26 when Typhoon “Lando” swept through the province. Experts have not been able to measure the depth of the hole at Sitio Kamangaan in Virac village. Two more houses are in danger of falling, according to Itogon Mayor Victorio Palangdan.

Fay Apil, director of the Mines and Geosciences Bureau (MGB) in Cordillera, said experts were still studying a break in the wall of a second diversion tunnel to determine if it caused the funnel-like void to open at the surface of Kamangaan.

The diversion tunnels were built in the 1960s to steer the Ambalanga River away from an old mine tailings facility. “It is not yet clear if [the tunnel breach] was the effect or the cause of the [Kamangaan] subsidence,” Apil said.

She said a team had been formed to conduct more examination of the tunnel.

The breach was detected when residents found debris like stonewalling materials and wood in the area. “But we have not found any trace of house parts from the six structures that fell into the hole,” Apil said.

She said the government’s priority is to determine the extent of the danger posed by the hole to know how many families should be relocated immediately.

Palangdan said the houses at the surface of the second diversion tunnel must be considered “compromised.”

The MGB initially examined two tunnels running beneath the community: the 450-m-long Vegas tunnel, which runs 57 m beneath Virac, and the 550-m-long drain tunnel, which discharges river water through two diversion tunnels. The old drain tunnel is 95 m below the Virac area where the hole was spawned.

The breach was discovered when the team explored the tunnel on Thursday.

Palangdan said the mining company had offered to take in the families who had lost their homes. They have been housed by a school which would need to reopen next week when classes resume.

Maricel Almandrez, 25, was renting one of the houses that were swallowed by the pit. Her husband works for the mine’s contractor.

“We lost everything, including what is left of our money until the next payday,” she said.

She said the void scares them. “It was as if a giant dinosaur sucked [our homes]. [When the first house fell], we heard what sounded like boiling water, then a faint thud before the ground shook and we ran for our lives,” she said.

She said many families were able to flee when a neighbor saw a tree vanish and she started alerting everyone.

“Our kitchen suddenly vanished. We ran in panic. We even forgot to wear our slippers. Outside my knees were trembling,” said Juanita Fontanos, 75, who lost her house.