More sinkholes reported in Bohol

MANILA, Philippines - Amid reports that sinkholes have appeared in southwestern Bohol, the Mines and Geosciences Bureau (MGB) yesterday said 20 sinkholes have been confirmed so far and more could turn up.

“Based on our geological mapping, there are still more,” said MGB director Leo Jasareno. “There are numerous sinkholes in the province based on our map interpretation.”

Most the sinkholes have an area of four meters by five meters and a depth of two meters and are located in the middle of barangays.

Some of the sinkholes, Jasareno said, pose no immediate danger to residents unless the capping or the topsoil of the sinkhole weakens. 

“These sinkholes may still widen and deepen but this will happen in geologic time, many years not in our lifetime,” he said.

He said a particularly large sinkhole that has not yet caved in was discovered in a school ground in Panggangan Island through the use of ground penetrating radar.

Radar imagery showed  that the sinkhole has a length of 100 meters and a depth of five to 10 meters.

“The sinkhole is located in the school grounds but is not directly under the school building,” said Jasareno.

The MGB, however, recommended the immediate evacuation of residents of Barangay Poblacion 1 in Tagbilaran City after a 5-meter by 4-meter sinkhole with a depth of two meters appeared in the barangay.

“We will recommend immediate evacuation in areas deemed dangerous,” said Jasareno.

The MGB chief noted that 80 percent of Bohol is made up of limestone, causing natural depressions like sinkholes to cave in as limestone deposits underneath erode.

The agency intends to complete the survey of sinkholes in Bohol by the end of the year.

It has already begun surveying sinkholes in Cebu City.

“We have started the survey in Cebu, but there is no immediate danger in the province,” he said.

Compared to numerous sinkholes that appeared in Bohol after the magitude 7.2 quake rocked the province, only one turned up in Cebu.

After the powerful earthquake struck the provinces in mid-October, a 15-meter wide sinkhole destroyed at least five houses.

The MGB is keeping an eye on Cebu because “all of Mactan” is limestone underneath.