05
Nov

PR 17 October 2013

The Mines and Geosciences Bureau (MGB) 7 of the Department of Environment and Natural Resources (DENR) 7 will send a senior geologist today to conduct a site assessment on the reported and recently formed sinkhole in Sitio Kapayas, Barangay Canjulao in Lapulapu City .

Based on the initial account, the collapse or cave-in of the cave roof which resulted to the formation of a sinkhole may have been trigged by the magnitude 7.2 earthquake and a string of aftershocks.

The earthquake may have caused ground or tension cracks.  These factors may have weakened the cave roof.

MGB-7 Regional Director Loreto B. Alburo said that Senior Science Research Specialist Abraham R. Lucero, Jr. will check the area.

As precautionary measures, Alburo added that MGB 7 initially recommended the appropriate installation of fence or barrier of the affected area, proper signage or warning, and continuous monitoring of the subsidence by the local government units.

A sinkhole was newly formed affecting 21 apartment units, which allegedly measures 20 meters by 15 meters in diameter and a depth of 1.8 meters.

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 rapid geohazard assessment on rain-induced landslides and flooding in 2009, a team of geologists from the MGB-7 observed the presence of sinkholes in 14 barangays in Cebu province.

“We encourage our communities to report immediately to their barangay officials if there are sinkholes that are forming and people should be kept away from these sinkholes, “ said DENR 7 Regional Executive Director Dr. Isabelo R. Montejo.

Eleven barangays in Tuburan, namely: Bulwang, Lusong, Montealegre, Santo Niño, Siotes, Kabkaban, Libo, Taminjiao, Kalangahan, Bagasawe, and Sandayong.

On the other hand, barangays Linut-od in Argao, Kang-actol in Dumanjug, and Vive in Ronda, Cebu were observed to have sinkholes.

According to the Visual Dictionary of the Earth, 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 in humic acids from the decay of vegetation.

It also said that 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.

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