Volcanic-tsunami hazard assessment - A case study from Heard Island and McDonald Islands, Australia

Volcanic-tsunami can occur with little warning, travel quickly (up to 1000km/hr) and cover great distances causing devastating impacts. There are several mechanisms for volcanic-tsunami events, including underwater explosion, blasts, pyroclastic flows, caldera collapse, subaerial failure and submarine failure. For the latter two, volcanic activity is not a pre-requisite, which presents additional challenges when raising awareness and undertaking planning activities. Volcanic-tsunami are often not considered in hazard and risk assessments, particularly as a far-field source. This can leave communities vulnerable to their impacts. It is estimated that 20-25% of fatalities directly attributable to volcanoes in the last 200-250 years have resulted from volcanic-tsunami (Latter, 1981; Auker et al., 2013) (e.g. ~36,000 deaths were a direct result of the tsunami generated from the 1883 Krakatau eruption). Moreover, volcanic-tsunami account for ~6% of tsunami events globally and can generate tsunami with a similar intensity to those from earthquake sources. In volcanically active regions the possibility of experiencing impacts from volcanic-tsunami is likely to be greater, highlighting a need for inclusion in hazard assessments. A volcanic hazard assessment that includes volcanic-tsunami can be as fundamental as an identification and characterisation of potential source volcanoes. More in-depth hazard assessments can then be produced through numerical modelling of propagation and inundation from tsunami generated in volcanic regions. In combination, this can provide an evidence base for undertaking more extensive analysis, or to provide guidance to planners who wish to consider potential impacts from lower frequency/higher consequence events. Here we present a method for classifying volcanoes for their potential to generate a tsunami and demonstrate the application of this method to the Heard Island and McDonald Islands (HIMI). HIMI are Australian Antarctic Territories located ~4000 km south west of Perth, Australia. Both of these eruptive centres have experienced violent, ongoing eruptive events; Heard Island as recently as 2016. Our analysis indicates that there is the potential for submarine mass failure at HIMI which could feasibly generate a tsunami detectable along the south-west Australian coast and in Antarctica. This poses a potential tsunami hazard to Australia, but more work needs to be undertaken to understand the mechanism and likelihood of such events. Presented at the 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI 2017)