ILOILO City – There are over 800 sinkholes in the world-famous Boracay Island off the northwest coast of Aklan province, and these put at risk the lives and properties in the country’s top tourist destination acclaimed for its fine white sand beaches.
The Mines and Geosciences Bureau of the Department of Environment and Natural Resources (MGB-DENR) counted 815 sinkholes in the island as of this year.
To minimize the risk of collapse, MGB recommended lessening the weight of structures in Boracay such as by having only one-storey buildings.
“Kung sobrang bigat ng structure, nag-a-add ng weight, plus the fact na natutunaw ‘yung ilalim. Only time can tell, ma-collapse gid na siya,” said Mae Magarzo, chief of MGB Region 6’s Geosciences Division.
A sinkhole is a hole in the ground that forms when water dissolves surface rock, often limestone, which is easily eroded, or worn away, by the movement of water, according to the National Geographic.
In a landscape where limestone sits underneath the soil, water from rainfall collects in cracks in the stone. Slowly, as the limestone dissolves and is carried away, the cracks widen until the ground above them becomes unstable and collapses, it explained.
The collapse often happens very suddenly and without very much warning.
“Wala na siya indication, gulpi lang siya,” said Magarzo.
In Boracay which is entirely limestone, the number of sinkholes has been increasing in recent years, according to MGB-6.
Its Karst Subsidence Hazard Mapping showed 789 sinkholes in 2018. These increased to 801 in 2019, 814 in 2020, and 815 from 2021 to 2022.
“That’s because ang chemical composition ng limestone is calcium carbonate. When it comes in contact with acid, unti-unti siyang matutunaw. Basta may water, lalo na acid rain,” said Magarzo.
Boracay’s Barangay Manoc-manoc has the most number of sinkholes – 293. The rest are in barangays Balabag and Yapak.
“That is why we want the carrying capacity of Boracay observed. As you could see in our geo-hazard map, almost all of the island is highly susceptible,” said Magarzo.
MGB-6 stressed the importance of constant monitoring of the ground and structures in Boracay.
“Since ara na siya, i-monitor lang nila kung may mapansin sila. Delikado eh. Ang problema lang namon, wala masyado mitigating measures kay iya na property ka limestone,” she said.
MGB-6 has already provided the local government unit of Malay, Aklan (which has jurisdiction over Boracay) and the Department of Public Works and Highways with the list of areas with sinkholes.
Boracay has a total land area of 10.32 square kilometers. It is approximately seven kilometers long, dog-bone shaped, with the narrowest spot being less than one kilometer wide.
Based on the study conducted by DENR-Ecosystems Research and Development Bureau in 2018 yet, the tourist carrying capacity of Boracay is 19,215 persons at any given time, or equivalent to 6,405 arrivals a day for a three-day stay. The ideal tourist arrival per day should be 6,085.
Meanwhile, the island’s population carrying capacity is 54,945 including the tourism carrying capacity. The existing population when the study was conducted in 2018 was 70,781 or an excess of 15,836 a day.
According to DENR regional executive director Livino Duran, they are yet to release an updated carrying capacity for Boracay./PN
