Tephra Hazard Around Izu Oshima and Aso Volcanoes, Japan: Application of the Automatically Generated Tephra Distribution Map

Abstract

Using discrete tephra mass loading/m² data from eruptions, this study attempted to draw their distribution maps using the algorithm developed by Yang and Bursik (2016). In the first approach, we used tephra observation data of the September 2014 Ontake and the October 2021 Aso eruptions to test the reproducibility of this automatically drawing distribution method for the previously reported hand-drawn tephra isopach maps and calculated eruption volumes. As a result, it was possible to reproduce each of the isopach maps and obtain similar total tephra volumes using this automatic drawing method. Therefore, it is possible to automatically obtain a tephra mass loading/m² distribution map without relying on the skills and experience of individual researchers, as was the case in the production of hand-drawn isopach maps. Based on the published tephra data for a series of eruptions at Izu Oshima and Aso Volcanoes over long periods of up to 1,500 and 30,000 years, respectively, the tephra distribution of each eruptive event was automatically drawn using the above method. By superimposing the results (digital data) of these tephra distribution maps for each volcano, it was possible to evaluate the long-term ash fall hazard at any location in each volcano.