800-Year-Old Eruption: Pre-Hispanic Bicolanos witnessed Isarog fury

By Jonas Cabiles Soltes

Isarog Volcano in Camarines Sur last erupted around the 12th century AD, a recent study presented at a geological conference has revealed.

The research, led by Timothy John E. Daita of the Department of Science and Technology-Philippine Institute of Volcanology and Seismology (DOST-PHIVOLCS) and the University of the Philippines-National Institute of Geological Sciences (UP-NIGS), confirmed that the volcano’s most recent eruption occurred approximately 800 years ago.

This eruption, according to the study, produced block-and-ash flows—dangerous avalanches of volcanic gases, ash, and rock fragments resulting from a dome collapse.

A significant find during the research was a fragment of a clay pot unearthed beneath volcanic deposits in Barangay Bagumbayan Grande, Goa, Camarines Sur. The artifact indicates that a settlement thrived in the area when the eruption occurred, providing valuable insight into the lives of pre-Hispanic Bicolanos.

5,400 Years of Volcanic Activity

The study documented five major eruptions of Isarog over the last 5,400 years, with eruptions dated to 3500 BC, 3000 BC, 2300 BC, 400 BC to the 1st century AD, and the 12th century AD.

Researchers collected charcoal and soil samples from various locations in Goa and San Jose towns for carbon-14 dating. Samples were taken from Barangays Bagumbayan Grande (Goa Terminal), San Isidro, and Napawon (Sitio Napanap) in Goa, as well as Barangay Pugay in San Jose. The carbon-14 dating analyses were conducted in laboratories in the United States.

The research estimates that Isarog Volcano erupts approximately every 1,000 years, based on calibrated ages. This timeline suggests that its last eruption occurred about 400 years before Spanish colonizers arrived in the Philippines.

Dome Collapses as a Primary Cause

The study highlighted that Isarog’s eruptions were predominantly caused by dome collapses, which triggered block-and-ash flows. These flows are known for their speed and destructive potential, posing significant risks to nearby settlements.

Goa, a major town in the Partido District, sits atop volcanic deposits from Isarog’s previous eruptions. This underscores the importance of continued monitoring and preparedness in the region.

Modern Monitoring Efforts

Isarog is one of 11 active volcanoes monitored by the Philippine Institute of Volcanology and Seismology. Data from Isarog’s monitoring stations is transmitted to the Mayon Volcano Observatory in Albay for analysis.

The study, conducted in collaboration with Dr. Christopher J. Harpel of the United States Geological Survey-Volcano Disaster Assistance Program (USGS-VDAP), Dr. Sandra G. Catane of UP-NIGS, Dr. Christopher G. Newhall, and Aljhon Q. Marco, provides valuable insights into Isarog’s eruptive history and its impact on early communities in the area.