Pre-eruptive excess volatiles and their relationship to effusive and explosive eruption styles in semi-plugged volcanoes

Understanding the role of various factors influencing eruption style is challenging, but it can aid in adapting different hazard mitigations and crisis responses for explosive or effusive events. Here, we focus on magma storage conditions controlling styles at basaltic andesite volcanoes, how they be related to monitoring data. We study cycle (1990, sub-Plinian) ? (2007, dome) (2014, eruptions from Kelud (Kelut) volcano, Indonesia. conducted petrological analyses products phase equilibria experiments using pumice explored a range temperatures, pressures, oxygen fugacity, volatile contents. show that reproduce main mineral assemblage (plagioclase ± pyroxenes magnetite amphibole olivine) phenocryst content (30–50 wt%) magmas three T = 975 39°C, p 175 25 MPa, f O 2 nickel–nickel oxide buffer, about 4–6 wt% water melt (ca. 3 5 ca. 4 7 1990 2014 eruptions, respectively). However, geothermobarometric results also indicate some crystals were sourced higher pressures. infer synthesis our data historical observations high 2007 dome (?70 likely resulted slow ascent toward surface alongside progressive degassing re-equilibration lower (?1 melt). Mass balance calculations sulfur budget 1990, 2007, events contained an excess fluid pre-eruptive conditions, propose this led their explosivity compared dome. The accumulation fluids during decadal-long repose depends plugged volcanic system is, its ability passively release magmatic fluids, prior eruption. Such condition could inferred records, including changes gravity plumbing over time, thus contribute better anticipate eruptive style.