Generation of a probabilistic volcanic ashfall hazard map of the 2020 Taal Eruption

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NOTE: This is the outline of the Invited Talk delivered online during the
13th UPLB CAS Student-Faculty Virtual Conference (SFRC 2020)
UPLB, 9 and 16 November 2020

Abstract

The phreatomagmatic eruption of Taal Volcano on January 12, 2020 dispersed heavy, water-laden ash across the Calabarzon region and Metro Manila, resulting in substantial agricultural and aquacultural losses. This study describes the generation of a probabilistic volcanic ashfall hazard map designed to quantify the spatial distribution and accumulation of tephra fallout under analogous eruptive conditions. Using the TephraProb probabilistic tephra-hazard framework, simulations were conducted with a Gaussian Tephra Transport and Dispersal Model (TTDM), which solves for ash particle advection–diffusion and settling under stochastic sampling of atmospheric states. Model parameterization incorporated eruption source parameters from the Smithsonian Global Volcanism Program, assuming a Volcanic Explosivity Index (VEI) of 3 indicative of Vulcanian to Sub-plinian plumes. Atmospheric forcing was derived from a decadal (2010–2019) archive of daily NOAA wind profiles, filtered to represent northeast-monsoon flow while excluding extreme tropical depression conditions to isolate climatologically typical dispersal regimes. Monte Carlo simulations over this parameter space yielded probabilistic isomass fields representing expected tephra loading (kg/m²) at the 50% exceedance probability. The resulting hazard maps provide essential baseline data for future validation with operational forecasts from the Philippine Institute of Volcanology and Seismology (PHIVOLCS), for evaluating risks to insurable commodity crops, and for informing resilient design standards for critical public infrastructure.

Keywords: Probabilistic hazard map, Tephra transport modeling, Taal Volcano, Ashfall dispersion

Talk Outline

Introduction
- Speaker Background: A university servant and researcher focused on finding computational solutions to agricultural and environmental problems
- Why is this worth our attention: The very recent 12 January 2020 eruption of Taal Volcano.
Definition of Terms
- Hazard Maps: A hazard map highlights areas vulnerable to specific dangers, while a probabilistic map incorporates probability conditions into the assessment.
- Volcanic Terminology: Tephra refers to all fragmental material ejected by a volcano (ash, cinders, bombs), while the plume is the column of this material rising during an eruption.
Motivation (Why is this interesting?)
- The 2020 Taal Eruption: The eruption ejected gases and unusually wet, heavy ash, causing significant damage to crops, livestock, and aquaculture structures.
- Spatial Impact: Satellite imagery and photographs document the spread of ashfall, which reached as far north as Bulacan.
Literature Review (What was done before?)
- Evolution of Transport Models: Previous research has evolved from theoretical dispersion models to complex Atmospheric Transport Models (ATMs) that account for weather and particle transport mechanisms.
- The Gaussian Approach: The Gaussian Tephra Transport and Dispersal Model (TTDM), utilized in the TephraProb toolbox, offers a computationally low-cost method by discretizing the atmosphere into vertical layers over flat topography.
Methodology (What did I do?)
- Model Configuration: The study utilized the TephraProb toolbox to implement a Gaussian TTDM for simulating the eruption.
- Data Parameterization: The model used NOAA wind profiles from 2010–2019 (filtered for monsoon seasons excluding tropical depressions) and Global Volcanism Program data for a VEI 3 eruption scenario.
Results (What happened?)
- Simulation Output: The primary output was a generated probabilistic hazard map displaying tephra isomass contours (kg/m²) for a VEI 3 event at a 50% probability of occurrence.
Future Directions (So, what now?)
- Validation and Application: Future work involves collaborating with PHIVOLCS for model validation and creating specific hazard maps for crop insurance and public works planning.
- Expansion of Scope: The project aims to develop an online scenario tool for generating hazard maps and to extend this methodology to other active volcanoes in the Philippines

References

BAYARRI MJ, JO Berger, ES Calder, AK Patra, EB Pitman, ET Spiller & RL Wolpert. 2015. Probabilistic quantification of hazards: A methodology using small ensembles of physics-based simulations and statistical surrogates. International Journal for Uncertainty Quantification 5(4):297-325. doi: 10.1615/Int.J.UncertaintyQuantification.2015011451.
BIASS S, C Bonadonna, L Connor & C Connor. 2016. TephraProb: A Matlab package for probabilistic hazard assessments of tephra fallout. Journal of Applied Volcanology 5:10. doi: 10.1186/s13617-016-0050-5.
BONADONNA C. 2006. Probabilistic modelling of tephra dispersion. In Mader HM, SG Coles, CB Connor & LJ Connor (eds.) Statistics in Volcanology. London: Geological Society of London pp. 243-259. doi: 10.1144/IAVCEI001.19.
HYMAN DM, A Bevilacqua & ML Bursik. 2019. Statistical theory of probabilistic hazard maps: A probability distribution for the hazard boundary location. Natural Hazards and Earth System Sciences 19:1347-1363. doi: 10.5194/nhess-19-1347-2019.
NAKAO Y & T Kusakabe. 2004. Procedure for making probabilistic seismic hazard map and understanding of the evaluated hazard. 13th World Conference on Earthquake Engineering, Vancouver, BC, Canada, 01-06 August 2004. Paper No, 793.
SIGURDSSON H, B Houghton, SR McNutt, H Rymer & J Stix (eds.). 1999. Encyclopedia of Volcanoes, 2nd ed. Elsevier.

Document from the Conference

Citation

PABICO JP. 2020. Generation of a probabilistic volcanic ashfall hazard map of the 2020 Taal Eruption. 13th UPLB CAS Student-Faculty Virtual Conference (SFRC 2020), UPLB, 9 and 16 November 2020.

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