It is official: Mt. Isarog is active

By Jonas Cabiles Soltes

TINAMBAC, Camarines Sur—Some 4300 years ago, Mount Isarog in Camarines Sur province emitted a fast-moving and burning mixture of gas and ash and other volcanic debris that travelled to as far as 20 kilometers away from its crater and burnt everything on its path.

A little-known study, which is being updated as of this writing, brought to the surface during a virtual gathering of geologists from all over the Philippines in 2020 the likelihood of that past eruption.

The study entitled “Paleomagnetic Determination of Pyroclastic Density Current Deposits in Tagontong and Bagumbayan Grande, Goa, Camarines Sur, Philippines and the Identification of Isarog Volcano’s Latest Eruption Age” was presented by its author Timothy John E. Daita at the convention of the Geological Society of the Philippines at the height of the Covid-19 pandemic.

Daita told the Bicol Mail in an online interview that he was updating for the University of the Philippines the same study on the eruptive history of Mount Isarog. This time, it covers the entire fourth district of Camarines Sur, not just Goa town.

Sleeping beauty or monster? Explosive past of Mt. Isarog still a threat, expert say.(https://upload.wikimedia.org/wikipedia/commons/1/19/Mt_Isarog_seen_at_Ocampo_Camarines_Sur.jpg)

Active volcano

The most imposing landmark of Camarines Sur, Mount Isarog rises to a height of approximately 1900 meters above sea level. It is surrounded by the towns of Goa, Tigaon, Ocampo, Pili, Tinambac, and Calabanga. At its western flank is Naga, the most densely populated city in Bicol Region.

Isarog was previously classified as a dormant or a potentially active volcano, but the Philippine Institute of Volcanology and Seismology (Phivolcs) recently reclassified it into an active volcano—as what is currently posted in the Phivolcs’ website—following the results of several studies especially the one conducted by Karen Fontijn and Christopher G. Newhall in 2013.

Fontijn and Newhall, in their study, assert that Isarog had “significant explosive eruptions and the latest of those volcanic activities occurred around 5000 years ago”.

Daita’s study however says that Isarog’s latest eruption could have been as recent as 4300 years ago, as it warns about the possibility of a hazardous eruption in the future.

“The identification of [volcanic] deposits in Bagumbayan Grande and Tagongtong suggests that a future eruption of Mount Isarog could generate similar hazards that could reach the downtown area of Goa, Camarines Sur, Philippines,” the study says.

It adds that the volcanic deposits in Goa could be a part of “a larger” deposit “that goes as far north as Lagonoy, Camarines Sur.”

The United States Geological Survey confirmed based on radiocarbon dating that the burnt coconut tree root found at the bottom of exposed rock layers near the transport terminal of Goa during the conduct of Daita’s study was about 4300 years old.

The charcoaled roots, found 12 kilometers from the crater, may have been scorched by the most recent eruption of Mount Isarog.

“Source of concern”

The study conducted under the guidance of Partido State University (PSU)and Newhall says the eruptive history of Mount Isarog is a “source of concern,” considering that the number of people living near [Isarog] totals almost 600, 000.

Fourteen thousand people live in downtown Goa alone, the study says, and “a future eruption of Mount Isarog can lead to catastrophic [volcanic materials] racing towards the populated areas of Goa.”

Phivolcs monitoring

Mount Isarog, along with Mayon, Bulusan, and Asog (Iriga), is one of the four active volcanoes in the region that Phivolcs closely monitors.

Government volcanologists installed a seismograph on Isarog in 2017 to detect volcanic activity.

A similar instrument was installed to monitor nearby Mount Asog (Iriga), another active volcano in Camarines Sur.