The 2020 Taal volcanic eruption in the Philippines: The role of satellite synthetic aperture radar data and source modeling during the crisis

Abstract:

On 12 January 2020, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) raised the alert status of Taal volcano from level 2 at 14h30 PST (Philippine Standard Time) to level 4 by 19h30 PST due to the rapid escalation of the volcanic activity, the latter meaning a hazardous eruption is imminent within hours to days. More than half a million people were directly affected by this crisis with reported ~$69M worth of damages to infrastructure and agriculture. Today, the alert level has been lowered to 1 indicating a low level of volcanic unrest.

Here we will present: 1) pre-eruptive interferometric synthetic aperture radar (InSAR) time-series from ALOS, ALOS-2, and ARIA-processed Sentinel-1 datasets from 2007-2019, 2) co-eruptive displacements derived from Sentinel-1 InSAR and pixel-offset analyses, and 3) post-eruptive Sentinel-1 InSAR time-series. On one hand, we are able to constrain the geometry and the location of the deformation source using the pre-eruptive time-series and the Caltech-JPL-developed AlTar v2.0 Bayesian inversion software. Results show an inflating ellipsoidal body located at ~5 km depth, beneath the NE portion of Volcano island. On the other hand, from the co-eruptive data, we inferred a deflating source with geometry and location that is consistent with the pre-eruptive source, and a ~21 km x ~8 km near-vertically dipping, NE striking dike with a uniform opening of ~4 m that extends SW from the Volcano Island. We calculated that if half the dike’s volume had erupted explosively the result might have yielded a VEI 4 eruption. Fortunately, the dike remained at depth and no catastrophic eruption occurred. To-date, persistent deformation can be observed at Taal, particularly within the Volcano Island and the Pansipit River Valley. NE trending ground fissures also emerged in the municipalities of Agoncillo, Lemery, San Nicolas, Taal, and Talisay due to the series of strong volcano-tectonic earthquakes in the area, corroborating the results of our model.

Another important aspect of this work is the near-real-time deliverance of the processed InSAR data, model, and analyses to PHIVOLCS while the eruption was happening. We will highlight the significant role of timely, open-access remote sensing data and discuss the potential for “adverse effects” during an on-going volcanic crisis.