Probabilistic Volcanic Ash Hazard Analysis (PVAHA) II: assessment of the Asia-Pacific region using VAPAH

Volcanic ash is an increasingly common, long-range hazard, impacting on our globalised society. The Asia-Pacific region is rapidly developing as a major contributor to the global population and economy and is home to one-quarter of the world’s active volcanoes. Here we present a regional-scale volcanic ash hazard assessment for the Asia-Pacific using a newly developed framework for Probabilistic Volcanic Ash Hazard Analysis (PVAHA). This PVAHA was undertaken using the Volcanic Ash Probabilistic Assessment of Hazard (VAPAH) algorithm. The VAPAH algorithm considered a magnitude-frequency distribution of eruptions and associated volcanic ash load attenuation relationships for the Asia-Pacific, and integrated across all possible events to arrive at an annual exceedance probability for sites of interest. The Asia-Pacific region was divided into six sub-regions (e.g. Indonesia, Philippines and Southeast Asia, Melanesia/Australia, Japan/Taiwan, New Zealand/Samoa/Tonga/Fiji and Russia/China/Mongolia/Korea) characterised by 276 source volcanoes each with individual magnitude-frequency relationships. Sites for analysis within the Asia-Pacific region were limited to land-based locations at 1-km grid spacing, within 500 km of a volcanic source. The Indonesian sub-region exhibited the greatest volcanic ash hazard in the region at the 100-year timeframe, with additional sources (in Japan, the Philippines, Papua New Guinea, Kamchatka - Russia and New Zealand) along plate boundaries manifesting a high degree of hazard at the 10,000-year timeframe. Disaggregation of the volcanic ash hazard for individual sites of interest provided insight into the primary causal factors for volcanic ash hazard at capital cities in Papua New Guinea, the Philippines and Japan. This PVAHA indicated that volcanic ash hazard for Port Moresby was relatively low at all timeframes. In contrast to this, Jakarta, Manila and Tokyo are characterised by high degrees hazard at all timeframes. The greatest hazard was associated with Tokyo and the PVAHA was able to quantify that the large number of sources impacting on this location was the causal factor contributing to the hazard. This evidence-based approach provides important insights for decision makers responsible for strategic planning and can assist with prioritising regions of interest for more detailed volcanic ash hazard modelling and local scale planning.