Spatiotemporal variations in eruption style, magnitude and vent morphology at Yasur volcano, Vanuatu: insights into the conduit system

Using visual, seismic, SO 2 -gas and thermal infrared data collected over 3 months, we observed systematic variations in the steady-state Strombolian-style activity of Yasur volcano. Observations reveal insights into the relationship between explosion magnitude and style with shallow conduit and magmatic conditions. Powerful eruptive phases are dominated by lava-rich activity, suggesting a high magma and volatile flux from depth that fills hot conduit pathways with mobile magma. Weak eruptive phases produced low-frequency ash-dominated explosions, indicative of cooling and stagnant magma near the top of the conduit and/or a debris layer covering the vent. Statistical forecast modelling was applied to explore if information on the previous days’ activity could forecast the next day and provide insights into multi-vent eruption patterns. Results suggest that North and South crater conduits are separated at significant depths and changes to either crater represent the variable proportions of magma and volatile flux directed into one pathway or the other. Zones A and B within the South crater have an alternating relationship, swapping between periods of active-inactive, or high-low magnitude. This appears to reflect the shallow diversion of magma and volatile flux between each vent, likely due to temporary conduit blockage and clearance cycles. Multiple timescales of eruptive behaviour change were revealed. Approximately 5-day cycles show changes in explosion parameters at individual vent zones, reflecting magma-level fluctuations and convection within the higher levels of each conduit. Cycles 10 to 20 days long occur in overall eruptive activity, and may reflect magma chamber processes that distribute magma and volatile flux differentially between the North and South conduits.