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The role of the crustal stress field in the incremental growth of plumbing systems

1 Ma. Antonia Bornas, 1 Christian Joseph Clarito, 1 Winchelle Ian Sevilla, 1 Paolo Reniva, 1 Rudy Lacson, 1 Eric Lino Arconado, 1 Paul Karson Alanis, 1 Princess Sharlene Cosalan, 1 James Noli Nobora, 1 Perla Delos Reyes, 1 Maricel Capa, 1 Dave Andrei Rivera, 2 Maurizio Battaglia and the PHIVOLCS Quick Response Team

  • Affiliations: 1 Department of Science and Technology-Philippine Institute of Volcanology and Seismology (DOST-PHIVOLCS); 2 United States Geological Survey–Volcano Disaster Assistance Program (USGS-VDAP)

  • Presentation type: Plenary talk

  • Presentation time: Friday – 04.07.25, 12:05 – 12:30, Room R380

Abstract

Eruptive activity at Taal’s Main Crater in Volcano Island (TVI) commenced on 12 January 2020, ending 43 years of repose. Alert Level 1 had been raised since March 2019 and reinforced with an advisory in December 2019 as elevated volcano-tectonic (VT) seismicity and continuous edifice inflation persisted. Precursory VT sequences at UTC 0330h 12 January preceded initial phreatic activity at 0500h concurrent with the onset of abrupt rapid tilt but sans physico-chemical changes in the Main Crater Lake. Verbal notifications within this period from PHIVOLCS to local village heads and government officials led to successful evacuation of human populations from TVI earlier than official issuance of Alert Level 2 at 0630h. The onset of phreatomagmatic activity was recorded visually at 0640h and of highly explosive activity at ~1000h coincident with peaks in seismic energy release. Alert Levels 3 and 4 were raised at 0800h and 1130h, respectively, the latter signalling evacuation of PDC-prone communities around Taal Lake. Peak eruption until 1600h generated an eruption plume >17 kilometers tall that dispersed ash over Taal Caldera and areas within ~100 kilometers north of TVI. This was followed in the next four days by VT and hybrid earthquakes along a northeast-trending inclined magmatic dike southwest of TVI and along-strike fissuring across Taal Caldera. Continuous GPS data recorded significant post-peak abrupt extension of the caldera, uplift of its northern sector and subsidence of TVI consistent with field observations of lakewater recession and coastal submergence. A total of 30-40 million cubic meters of magma was approximated from GPS inversion and well-constrained tephra dispersal mapping, consistent with VEI3. The eruption waned by 13 January and on 19 January, but unrest recurred on March 2021 with long-period earthquake swarms, elevated SO2 degassing and minor eruptive activity.

We discuss the outcomes and insights over five years of unrest at Taal with implications to volcano monitoring, early warning and community engagement.