RAPID: The effusive to explosive transition of La Soufrière, St. Vincent: Insights from petrology and hygrometry

点击翻译按钮获取中文摘要

The on-going eruption of La Soufrière provides the unique opportunity to understand and evaluate a volcanic event as it is occurring and evolving in almost real-time. Unique to this study, mineral hygrometry will be applied to assess the pre-eruptive water content dissolved in the melt, as recorded by the crystallization of phenocryst rims and/or microlites in scoria from the first eruptive phases on April 9th and 10th. If a buildup of volatiles is driving the eruption, one would expect to see that reflected in the water content recorded by the mineral phases. One can also readily determine if magma mixing was an eruption trigger by comparing the zoning profiles of co-existing minerals, as magma mixing and degassing result in contrasting patterns. Using crystal size distribution and textures of microlites will enable decompression pathways to be estimated and ascent rates of the explosive phase better understood. The magma chamber conditions just prior to the eruption can also be estimated. When combined with similar data from the effusive 2021 lava dome or lithics entrained in the explosive deposits, the causes of the differences in eruptive style can be established. This effort will be useful to the authorities monitoring the eruption. It is a substantive international collaboration and will fund the research of undergraduates.In late December 2020, a lava dome began extruding in the summit crater of La Soufrière, a stratovolcano on the eastern Caribbean island of St. Vincent, after exhibiting no volcanic activity since 1979. On April 9th, 2021, the eruptive style transitioned to an explosive phase, with multiple Plinian events in the first few hours of eruption. Based on the recommendation of the UWI Seismic Research Centre (UWI-SRC), the official agency for monitoring the ongoing eruption, the government of St. Vincent issued an evacuation of the red zone (16,000 people) less than 24 hours prior to the eruption. The transition from effusive to explosive behavior was abrupt and it is unclear what mechanism triggered the ash venting phase, which has severely affected St. Vincent with significant ashfall (also affecting neighboring Barbados and St. Lucia), pyroclastic density currents, and lahars. Throughout the changing eruption styles, La Soufrière has been extensively monitored using seismicity, ground deformation, gas emissions, and remote sensing by the UWI-SRC. Based on gas emission and water geochemistry data obtained by the PIs during the effusive phase, we hypothesize that the magmatic system was not degassing, leading to a buildup of volatiles which eventually triggered the eruption. Using various petrologic tools, this hypothesis shall be tested and the likelihood of similar behavior in the future shall be assessed. This effort will be useful to the authorities monitoring the eruption. It is a substantive international collaboration and will fund the research of undergraduates.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.