Volcanic ballistic projectile deposition from a continuously erupting volcano: Yasur Volcano, Vanuatu

Abstract

Volcanic Ballistic Projectiles (VBPs) are the main hazard to life and infrastructure from Strombolian eruptions. This type of eruption involves moderate bursts of expanding gases that eject clots of incandescent lava in cyclical or nearly continuous small eruptions. This eruption style is a tourist drawcard, exposing people to VBP hazard. Most of the research on VBPs to date has been focussed on understanding how they form and their trajectory. However, little focus has been placed on how they are located and distributed within VBP fields. There is also little inclusion of these data into hazard and risk assessments. In this study, we used a drone to image the east and south flanks of Yasur Volcano, Vanuatu, and cameras, infrasound, and seismicity to record explosions from 28 July to 2 August and 17 to 19 October 2016. We present the map of VBPs from the two trips, assessing how the VBP field changes with distance and direction from the vent, and how eruption dynamics influence these changes. We found that the VBP spatial density and median diameter decrease with distance from the crater. Spatial density was also found to vary with direction around the crater, with higher spatial densities found in the S–SSE direction. Combined with our observations, we attribute the changes in spatial density to the direction of explosions. This means there will be considerable variation in summit VBP hazard and is an important consideration for hazard and risk assessments.