Evaluating and ranking Southeast Asia's exposure to explosive volcanic hazards

Abstract

Abstract. Regional assessments provide a large-scale comparable vision of the threat posed by multiple sources and are useful for prioritising risk-mitigation actions. There is a need for such assessments from international, regional and national agencies, industries and governments to prioritise where further study and support could be focussed. Most existing regional studies on the threat posed by volcanic activity have relied on concentric radii as proxies for hazard footprints and have focused only on population exposure, often using indices to make first-order estimates of exposure. However, this approach is an oversimplification of volcanic hazards and their associated impacts. We have developed and applied a new approach that quantifies and ranks exposure to multiple volcanic hazards for 40 high-threat volcanoes in Southeast Asia. For each of our 40 volcanoes, hazard spatial extent, and intensity where appropriate, was probabilistically modelled for four volcanic hazards across three eruption scenarios, giving 697,080 individual hazard footprints plus 19,560 probabilistic hazard outputs. We then developed a GIS framework to overlay the spatial extent of probabilistic hazard footprints with open-access datasets across five exposure categories. Finally, we used our calculated exposure values to rank each of the 40 volcanoes in terms of the threat they pose to surrounding communities. We present VolcGIS, an open-source Python code that implements all of the spatial operations required for exposure analysis, available at github.com/vharg/VolcGIS. We provide all our outputs - more than 6,500 geotif files and 70 independent estimates of exposure to volcanic hazards across 40 volcanoes - in user-friendly format. Results highlight that the island of Java in Indonesia has the highest median exposure to volcanic hazards, with Merapi consistently ranking as the highest threat volcano. Hazard seasonality, as a result of varying wind conditions affecting tephra dispersal, leads to increased exposure values during the peak rainy season (January, February) in Java, but the peak dry season (January, February, March) in the Philippines. A key aim of our study was to highlight volcanoes that may have been overlooked, perhaps because they are not frequently or recently active, but that have the potential to affect large numbers of people and assets. It is not intended to replace official hazard and risk information provided by the individual country or volcano organisations. This study and the tools developed provide a road map for future multi-source regional volcanic exposure assessments, with the possibility to extend the assessment to other geographic regions and/or towards impact and loss.

Large Uncertainties Are Pervasive in Long-Term Frequency-Magnitude Relationships for Volcanoes in Southeast Asia

“…Over half of our study volcanoes in the region did not have sufficient eruption records to allow for Bayesian updating, including volcanoes that have a very high population exposure index (PEI 7), for example Malabar, Tampomas, and Penanggungan. Thus, a priority research area would be to obtain a broad understanding of the eruption history of high exposure/low data volcanoes (Jenkins et al, 2021). This is particularly important as recent history has examples of major eruptions affecting communities from volcanoes that had not previously erupted during historical times or had underestimated frequencies of eruption.…”

Linking hazard intensity to impact severity: mini review of vulnerability models for volcanic impact and risk assessment

“…As society's exposure to volcanic hazards increases (Chester et al, 2000;Auker et al, 2013;Jenkins et al, 2022), it is necessary to build a comprehensive understanding of how societal elements (e.g., people, buildings, farms) will perform during future volcanic events (Jenkins et al, 2014;Wilson et al, 2014;Deligne et al, 2022). One common method of acquiring this knowledge is through the development of vulnerability models, which describe the relationship between the intensity of a hazard (e.g., tephra deposit thickness) and a corresponding impact to society (e.g., damage, disruption) (Figure 1).…”

Lahar events in the last 2,000 years from Vesuvius eruptions. Part 3: Hazard assessment over the Campanian Plain

“…Furthermore, detailed lists of documented lahars in the 20th century are available in the literature (Fiorillo & Wilson, 2004). Despite such evidence, up to now most of the Probabilistic Volcanic Hazard Assessments (PVHA) for this region has mostly focussed on PDCs (e.g., Neri et al, 2008;Gurioli et al, 2010;Neri et al, 2015;Sandri et al, 2018;Tierz et al, 2017) and tephra fallout (e.g., Costa et al, 2009;Selva et al, 2010;Sandri et al, 2016;Selva et al, 2018;Massaro et al, 2023), while systematic quantitative hazard assessments from lahars (see for example Jenkins et al, 2022) have been lacking. An exception is provided by Tierz et al (2017), who applied a Bayesian Belief Network to assess the effect of different factors (linked to rainfall intensity and volcanoclastic volume) on the probability of different initial volumes of lahars.…”