Residents in Aklan island bewildered after small hills appear every low tide

Residents from Tabon Island in Batan, Aklan were puzzled after small, Chocolate Hill-like slopes began to appear on the shore every time the sea is on low tide.

According to Kuya Kim's report on "24 Oras," Thursday, the hills were captured on video by fisherman Jay-Ar Candelario.

"Tuwing low tide makikita po siya nang maramihan. 'Yung taas niya 20 inches. Tawag namin doon bukid-bukid. Parang bulkan po siyang pumuputok. Putik lang po 'yung lumalabas tsaka tubig," Jay-Ar said.

He also noticed that, as time goes by, they grow taller and bigger.

According to an expert, the small hills Jay-Ar captured were sand boils or sand volcanoes.

Although a sand boil is shaped like a volcano, it is not considered one and does not emit lava.

"Ito ay natural landforms. Tinatawag itong volcano dahil sa conical shape at morphology nito. At tinatawag naman itong sand boils dahil sa paraan ng paglabas ng materials doon sa vent or butas kung saan bumubulwak 'yung tubig na may kasamang buhangin," geologist Mar Christian Cruz said.

Sand boils are formed because of the pressure variation between the water-saturated sand layer at the bottom and the surface sand layer.

"Dahil sa compaction sa ibabaw at 'yung nabubuong upward pressure sa ilalim nape-puwersa 'yung tubig na may kasamang buhangin na ma-eject o ma-release sa surface," he said.

"Kadalasan nao-observe ito sa sandy areas na malapit sa bodies of water. Pero puwede rin itong manifestation na may liquefaction sa lugar gawa ng paglindol," he added.

It is not dangerous, but the expert said that it may affect the structures in the vicinity.

"Much better kung magkaroon ng field inspection ang concerned government agencies para ma-identify 'yung mga geohazards na associated dito," he said.

—Carby Basina/MGP, GMA Integrated News