DENR geologist to study sinkhole in Cebu

MANILA, Philippines - The Department of Environment and Natural Resources, through the Mines and Geosciences Bureau (MGB), is sending a geologist to Kinatarcan islet in Santa Fe, northern Cebu following a sinkhole that formed in the area.

The sinkhole, which the Office of the Civil Defense Central Visayas confirmed, reportedly measures 40 feet in diameter and has a depth of about 40 feet.

It was discovered and reported by residents in the area yesterday.

The Cebu Provincial Disaster Risk Reduction Office said 30 families have been evacuated from the area.

MGB-7 director Loreto Alburo recommended the fencing of the area and putting up signage to warn people of the danger in going there.

“I strongly advised local government officials to strictly not allow people to come near the sinkhole as we are still determining the extent of its formation,” Alburo said.

He said MGB-7’s geosciences division chief Al Emil Berador would check the area.

Sinkholes are common where rocks below the land surface are limestone and carbonate that can naturally be dissolved by circulating ground water.

As rocks dissolve, spaces and caverns develop underground. The surface land usually stays intact until there is not enough support. Then, a sudden collapse of the surface can occur.

This was manifested by the sinkholes that formed following the magnitude 7.2 earthquake that struck Central Visayas last year, Alburo said.

As of July 25, about 205 sinkholes have been recorded in Bohol alone.

The Visual Dictionary of the Earth said caves commonly form in areas of limestone. Limestone is made of calcite (calcium carbonate), which dissolves in the carbonic acid naturally present in rainwater and humid acids from the delay of vegetation.

The acidic water trickles down through cracks and joints in the limestone and between rock layers, breaking up the surface terrain into clints (blocks of rock), separated by grikes (deep cracks) and punctuated by sinkholes into which surface streams may disappear.