70 sinkholes found in northern Cebu after quake

“Ang limestone kasi is may inherent solubility. Madali siyang matunaw, so with the aid of rainwater that reacts with carbon dioxide in the atmosphere, it forms carbonic acid,” Aleta said.

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She said this weak acid seeps through the soil and slowly dissolves limestone, creating underground voids that eventually collapse during earthquakes.

When the roofs of these caves cave in, sinkholes appear on the surface — and the danger increases when the underground voids are interconnected, which could cause wider subsidence.

Aside from natural cave collapses, MGB-7 also noted ground depressions in clay-rich areas, where heavy rainfall pulls down soil layers as water seeps deeper underground.

Aleta added that around 70 percent of Cebu Island is underlain by limestone, making it naturally prone to sinkhole formation. The same condition extends to Bohol, Negros Oriental, and Siquijor.