Geologists from the University of the Philippines (UP) Diliman identified evidence of extreme wave events preserved in large coastal boulders in Pasuquin, Ilocos Norte — findings that could help coastal communities better prepare for similar hazards in the future.
Edrian Tubalado of the UP National Institute of Geological Sciences said that analyzing the boulders allows his team to reconstruct past extreme wave events, such as tsunamis and intense storms, estimate their intensity, and date their occurrence.
The findings could help local government units and communities strengthen hazard preparedness through better evacuation plans, building codes, and resilient coastal infrastructure.
Tubalado explained that the boulders are primarily made of fossilized corals called coastal carbonate boulders. He said his team measured the boulders’ size, weight, and location, then used specialized dating techniques to determine the ages of the coral components.
“These ages tell us when the coral boulders were transported out from the seawater onto the coast,” Tubalado said.
He added that the boulders’ size and weight, such as a 31-ton boulder logged in their study, reveal how powerful the waves were.
The study also revealed that in the town of Pasuquin, waves can reach around four meters high.
“Our spatial analysis showed that certain areas are more prone to boulder deposition and damage. For example, areas with embayments, or coastal indentations, and steeper nearshore slopes experienced more intense wave energy. This helps identify which areas face the greatest risk,” Tubalado said.
“As climate change potentially increases the intensity of tropical cyclones, understanding the historical baseline of extreme wave events becomes even more critical for predicting future risks and helping coastal communities adapt accordingly,” he added.
The study is titled “Extreme wave events inferred from large subaerial carbonate boulders on a rocky coast in Pasuquin, Ilocos Norte, Philippines.” It was published in Marine Geology, a journal focused on marine geological processes.
