Volcanic ash presents a natural hazard with a global reach, as ash can be transported up to thousands of kilometers from a given volcanic eruption to cross national boundaries and impact vulnerable environmental and societal elements. Given the widespread nature of ash hazard and increasing levels of globalisation, an understanding of the likelihood of hazard on progressively wider scales is important for long-term strategic planning. Here we present results from a regional-scale assessment of ash hazard in the Asia-Pacific determined using a new method developed at Geoscience Australia.
The Probabilistic Volcanic Ash Hazard Analysis (PVAHA) technique was used to approximate volcanic tephra hazard for 276 volcanoes in the Asia-Pacific (those meeting certain selection criteria). The synthetic catalogue of events in PVAHA includes tephra-load decay relationships to account for uncertainty in the eruption parameters e.g. eruption magnitude, column height, duration, tephra dispersal parameters, and wind velocity. The ash-load (kg/m2) for each site (on a 5 degree grid) at ground level was simulated for each synthetic event in the catalogue when paired with the magnitude-frequency relationships for the region. A total of 178935 sites were calculated, covering a region of approximately 4,600,000 km2, allowing a quick assessment of the relative ash hazard for countries within the study area.
This Asia-Pacific case study demonstrates the applicability of the PVAHA approach to modelling uncertainty for volcanic ash hazard on regional scales. This regional-scale assessment should not be used as an alternative to tested and accepted methods of undertaking local scale hazard modelling (e.g. dispersal modelling) or for local scale decision-making; rather, it should be employed as a tool to rapidly assess the relative hazard in a regional to global sense enabling determination of at-risk areas which would benefit from more detailed hazard and risk analysis at the local scale.
