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Harris, Chris
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- PublicationRestrictedMagmatic stoping during the caldera-forming Pomici di Base eruption (Somma-Vesuvius, Italy) as a fuel of eruption explosivity(2020)
; ; ; ; ; ; ; ; ; Magma-carbonate interactions and the subsequent CO2 release can occur before and during an eruption, critically affecting magma storage and ascent processes. However, the mechanisms and timescales of those interactions are unclear, particularly during the fast magma withdrawal that feeds high-intensity eruptions. In order to better understand magma‑carbonate interactions, we selected the caldera-forming Pomici di Base plinian eruption, the oldest (22 ka) and largest (> 4.4 km3) explosive event in the history of the Somma-Vesuvius volcanic system, as case study. During this event the emission of trachytic and latitic-shoshonitic (~25% and ~75% of the erupted magma volume respectively) magmas generated a long-lasting plinian column, hypothetically driven by CO2 liberation during magma‑carbonate interaction. In this study, we reconstruct in detail the evolution of the plumbing system during the Pomici di Base eruption combining geochemical (major/minor elements and radiogenic/stable isotopes) analyses of juvenile products with thermodynamic and kinetic calculations. Our results demonstrate that magmatic stoping (i.e., the formation and transport of host-rock pieces into a magma body) during caldera collapse evolution can promote rapid magma assimilation of carbonate blocks and CO2-rich fluids resulting from destabilization of the carbonate bedrock, thus triggering CO2 release and acting as a fuel for the eruption explosivity, especially when residual hot mafic magmas are involved. Our findings suggest that the accurate knowledge of these processes and their influence on eruptive dynamics are critical for improving the hazard assessments of volcanoes with plumbing systems located in carbonate bedrocks.526 6 - PublicationOpen AccessMagma reservoir dynamics at Toba caldera, Indonesia, recorded by oxygen isotope zoning in quartz(2017-01)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ;Quartz is a common phase in high-silica igneous rocks and is resistant to post-eruptive alteration, thus offering a reliable record of magmatic processes in silicic magma systems. Here we employ the 75 ka Toba super-eruption as a case study to show that quartz can resolve late-stage temporal changes in magmatic δ18O values. Overall, Toba quartz crystals exhibit comparatively high δ18O values, up to 10.2‰, due to magma residence within, and assimilation of, local granite basement. However, some 40% of the analysed quartz crystals display a decrease in δ18O values in outermost growth zones compared to their cores, with values as low as 6.7‰ (maximum Δcore−rim = 1.8‰). These lower values are consistent with the limited zircon record available for Toba, and the crystallisation history of Toba quartz traces an influx of a low-δ18O component into the magma reservoir just prior to eruption. Here we argue that this late-stage low-δ18O component is derived from hydrothermally-altered roof material. Our study demonstrates that quartz isotope stratigraphy can resolve magmatic events that may remain undetected by whole-rock or zircon isotope studies, and that assimilation of altered roof material may represent a viable eruption trigger in large Toba-style magmatic systems.480 80 - PublicationOpen AccessMulti-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions(2018-07-12)
; ; ; ; ; ; ; ;; ;; ; ;The island of Bali in Indonesia is home to two active stratovolcanoes, Agung and Batur, but relatively little is known of their underlying magma plumbing systems. Here we define magma storage depths and isotopic evolution of the 1963 and 1974 eruptions using mineral-melt equilibrium thermobarometry and oxygen and helium isotopes in mineral separates. Olivine crystallised from a primitive magma and has average δ18O values of 4.8‰. Clinopyroxene records magma storage at the crust-mantle boundary, and displays mantle-like isotope values for Helium (8.62 RA) and δ18O (5.0-5.8‰). Plagioclase reveals crystallisation in upper crustal storage reservoirs and shows δ18O values of 5.5-6.4‰. Our new thermobarometry and isotope data thus corroborate earlier seismic and InSAR studies that inferred upper crustal magma storage in the region. This type of multi-level plumbing architecture could drive replenishing magma to rapid volatile saturation, thus increasing the likelihood of explosive eruptions and the consequent hazard potential for the population of Bali.106 30