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Sinkholes may occur in Cebu

Friday, June 4, 2010 [ ]

THERE is a big possibility that a sinkhole similar to the one that formed in Guatemala City will appear in Cebu, even in urban areas, a geologist said yesterday.
The Guatemala City sinkhole caught the attention of people all over the world because of its size, which is reportedly 66 feet across and 100 feet deep.
Al Emil Berador, chief geologist of the Mines and Geosciences Bureau (MGB) Central Visayas, said sinkholes can appear in Cebu because a large area of the island is composed of limestone.
Berador said sinkholes are natural formations that occur after limestone deposits gradually corrode when in contact with weak carbonic acid, a combination of water and carbon dioxide.
Carbonic acid can gradually corrode hard limestone, which explains why there are limestone caves, said Berador.
Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or 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 no longer enough support. Then, the surface area can suddenly collapse.
Berador said majority of the areas in Cebu have limestone deposits.
About 60 to 70 percent of Cebu, including areas that are habitable such as urban areas, is composed of limestone, he said.
Berador said a sinkhole can only occur if a corroded limestone area is disturbed by natural tremors such as earthquakes or by human-induced activities.
He said the only way to detect if an area is susceptible to sinkhole formation is through core drilling or ground-penetrating radar.
Berador said there have been sinkhole formations in some areas in Central Visayas.
A few years back, a massive sinkhole formed in Anda town in Bohol after an earthquake hit the area. Berador said the sinkhole swallowed a couple of houses.
He also said there are sinkholes in Barangay Talamban in Cebu City and Barangay Cabancalan in Mandaue City. Berador said the sinkhole in Cabancalan was found in an area being developed by a private firm. (JKV)
Published in the Sun.Star Cebu newspaper on June 4, 2010.

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