The Mines and Geosciences Bureau-7 has upheld their earlier recommendations on the immediate installation of a permanent fence, continuous monitoring of the ground subsidence, and proper signage or warning.

This came after Senior Science Research Specialist Abraham R. Lucero Jr. conducted a site assessment following a reported and recently formed sinkhole in Sitio Plaza, Barangay Camboang, in Dumanjug, southwest Cebu, which has been considered as very critical for ground subsidence.

The sinkhole, which measures 10 meters by 8.5 meters in diameter and a depth of three to four meters, has a distance of 11 meters from the barangay road.

MGB-7 Regional Director Loreto B. Alburo said it issued a landslide threat advisory on the significant findings and recommendations, which is addressed and received by Barangay Captain Meliza Mae Quirante of Barangay Camboang and Dumanjug Mayor Nelson F. Garcia.  The advisory, he said, emphasized the threat of ground subsidence.

A sinkhole, also known as a sink, shake hole, swallow hole, swallet, doline or cenote is a natural depression or hole in the surface topography caused by karst processes – the chemical dissolution of carbonate rocks.

Meanwhile, the affected area is underlain or carpeted with pliocene to pleistocene carcar formation which is characterized as dominantly limestone, and poorly bedded to massive, partly dolomitic with abundant marine fossils.

It also found out that the affected area has an indication of an existing subterranean river system or a water channel.

The collapse or cave-in of the cave roof which resulted to the formation of a sinkhole has been attributed due to the 6.9 magnitude earthquake and many aftershocks, and intense and prolonged rain.

Sinkholes are common where the rock below the land surface is limestone, carbonate rock, rocks that can naturally be dissolved by circulating ground water. As the rock dissolves, spaces and caverns develop underground. These sinkholes can be dramatic because the surface land usually stays intact until there is not enough support. Then, a sudden collapse of the land surface can occur.

“We urge our local officials to report immediately to the MGB-7 if there are occurrences of sinkhole formations and to continuously monitor such sinkhole to avoid further damage to lives and properties,” Alburo added.

“Our communities are also reminded to be vigilant and to avoid settlement near the affected area,” he said.