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M
Geiger, H, Troll VR, Jolis EM, Deegan FM, Harris C, Hilton DR, Freda C.  2018.  Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions. Scientific Reports. 8   10.1038/s41598-018-28125-2   AbstractWebsite

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 delta O-18 values of 4.8%. Clinopyroxene records magma storage at the crust-mantle boundary, and displays mantle-like isotope values for Helium (8.62 R-A) and delta O-18 (5.0-5.8%). Plagioclase reveals crystallisation in upper crustal storage reservoirs and shows delta O-18 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.

S
de Moor, JM, Fischer TP, Sharp ZD, Hauri EH, Hilton DR, Atudorei V.  2010.  Sulfur isotope fractionation during the May 2003 eruption of Anatahan volcano, Mariana Islands: Implications for sulfur sources and plume processes. Geochimica Et Cosmochimica Acta. 74:5382-5397.   10.1016/j.gca.2010.06.027   AbstractWebsite

Sulfur isotope compositions of pumice and adsorbed volatiles on ash from the first historical eruption of Anatahan volcano (Mariana arc) are presented in order to constrain the sources of sulfur erupted during the period 10-21 May, 2003. The isotopic composition of S extracted from erupted pumice has a narrow range, from delta S-34(V-CDT) +2.6 parts per thousand to +3.2 parts per thousand, while the composition of sulfur adsorbed onto ash has a larger range (+2.8 parts per thousand to +5.3 parts per thousand). Fractionation modeling for closed and open system scenarios suggests that degassing of SO2 raised the delta S-34(V-CDT) value of S dissolved in the melt from an initial composition of between +1.6 parts per thousand and +2.6 parts per thousand for closed-system degassing, or between -0.5 parts per thousand and +1.5 parts per thousand for open-system degassing, however closed-system degassing is the preferred model. The calculated values for the initial composition of the magma represent a MORB-like (delta S-34(V-CDT) similar to 0 parts per thousand) mantle source with limited contamination by subducted seawater sulfate (delta S-34(V-CDT) +21 parts per thousand). Modeling also suggests that the delta S-34(V-CDT) value of SO2 gas in closed-system equilibrium with the degassed magma was between +0.9 parts per thousand and +2.5 parts per thousand. The delta S-34(V-CDT) value of sulfate adsorbed onto ash in the eruption plume (+2.8 parts per thousand to +5.1 parts per thousand) is consistent with sulfate formation by oxidation of magmatic SO2 in the eruption column. The sulfur isotope composition of sulfate adsorbed to ash changes from lower delta S-34 values for ash erupted early in the eruption to higher delta S-34 values for ash erupted later in the eruption. We interpret the temporal/stratigraphic change in sulfate isotopic composition to primarily reflect a change in the isotopic composition of magmatic SO2 released from the progressively degassing magma and is attributed to the expulsion of an accumulated gas phase at the beginning of the eruption. More efficient oxidation of magmatic SO2 gas to sulfate in the early water-rich eruption plume probably contributed to the change in S isotope compositions observed in the ash leachates. (C) 2010 Elsevier Ltd. All rights reserved.