Photogeologic Map of Biliran Island
Photogeologic Map of Biliran Island

Prof. Rolando Borrinaga
First Posted 03:50 PM January 17, 2018

With nine minor earthquakes rocking Biliran Province since yesterday, our people now echo Ralph Waldo Emerson’s warning, “We learn geology the morning after the earthquake.” The accompanying graphic here shows the Photogeologic Map of Biliran Island, published by the Philippine Institute of Volcanology and Seismology in 2000. It is self-explanatory in many details and should serve as a vital reference and guide for all of us in this time of disaster and “climate change.”

Biliran has the only active volcano in Eastern Visayas at present. It is labeled Bilitan Volcano in PHIVOLCS literature, and it is found in the Suiro Volcano Complex on the south-central part of the island. This is where the controversial sulfur mining field is also found, a tiny patch of ground mined for centuries compared to the much wider adjacent area cleared up by the Biliran Geothermal, Inc. (BGI) for their geothermal exploratory drillings, right from the top of an active volcano (and not from a farther side), which makes this project both unique and dangerous for our people.

I have established the timeline of the volcanic eruptions in Biliran during historic times. The most recent eruption was in 1939, and this minor explosion was on Mt. Suiro, right where the sulfur mining area and the BGI drillings are. I have a digital copy of the investigation report of the geological team sent to the area after the 1939 event somewhere in my files. The previous eruption was around 1800, or 139 years earlier, a major event which was described in a document on the Caibiran pueblo that I had photo-copied from the Philippine National Archives. I had thought the eruption came from Mt. Gumansan (Matin-ao to the locals) or Mt. Sayao. But since the map shows that both are domes and not volcanoes, the eruption could only have come from Asluman Volcano (Mt. Camalubaguhan to the locals), because the lahar flowed through Tinago River towards Caibiran.

The previous major eruption was that of Panamao Volcano north of the island, which I had estimated to have happened around 1669, or 131 years earlier than the 1800 event. The Jesuit missionary Fr. Francisco Alcina had described this volcano as eruptive in 1668. My estimate for the eruption was premised on a recorded ashfall in Tacloban’s local history in 1669. The explosion must have been a violent and destructive one, sufficiently enough for the natives to rename the island from Isla de Panamao to Isla de Biliran.

Inferring a pattern from the three later eruptions I speculated a volcanic eruption in Biliran as early as 1521, just before the arrival of the Magellan expedition in the Philippines. The involved volcano might have been Tagburok Volcano (Camburok to the locals) overlooking the ancient village of Nasombol (lit., Became a symbol of a great victory), on the present Sitio Ilawod of Brgy. Caraycaray in Naval. A theory I had published in 1995 has it that Lapu-lapu hailed from this place, and that he was the historical person referred to as Bagasumbul (like a symbol of a great victory), the popular old name of Naval.

During the extended run of the “Amaya” epic-series on GMA-7 in 2012, I proposed the scenario that a volcano eruption around 1521 forced Lapulapu and his fellow villagers to flee Bagasumbul and take refuge in Mactan, the domain of his father. This is where he would have a date with recorded history through his conquest of Magellan. The scenario was accepted and dramatized in the concluding episode of “Amaya,” where the narrating babaylan (priestess) said that a volcanic eruption signaled the coming of a major change that would alter their lives forever – the arrival of the Westerners. Never mind that it started with the victory in Mactan. But this is another story.

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