Explosive activity on Kīlauea’s Lower East Rift Zone fuelled by a volatile-rich, dacitic melt

Abstract

Magmas with matrix glass compositions ranging from basalt to dacite erupted from a series of 24 fissures in the first two weeks of the 2018 Lower East Rift Zone (LERZ) eruption of Kīlauea Volcano. Eruption styles ranged from low spattering and fountaining to strombolian activity. Major element trajectories in matrix glasses and melt inclusions hosted by olivine, pyroxene and plagioclase are consistent with variable amounts of fractional crystallization, with incompatible elements (e.g., Cl, F, H2O) becoming enriched by 4-5 times as melt MgO contents evolve from 6 to 0.5 wt%. The high viscosity and high H2O contents (~2 wt%) of the dacitic melts erupting at Fissure 17 account for the explosive Strombolian behavior exhibited by this fissure, in contrast to the low fountaining and spattering observed at fissures erupting basaltic to basaltic-andesite melts. Saturation pressures calculated from melt inclusions CO2-H2O contents indicate that the magma reservoir(s) supplying these fissures was located at ~2-3 km depth, which is in agreement with the depth of a dacitic magma body intercepted during drilling in 2005 (~2.5 km) and a seismically-imaged low Vp/Vs anomaly (~2 km depth). Nb/Y ratios in erupted products are similar to lavas erupted between 1955-1960, indicating that melts were stored and underwent variable amounts of crystallization in the LERZ for >60 years before being remobilized by a dike intrusion in 2018. We demonstrate that extensive fractional crystallization generates viscous and volatile-rich magma with potential for hazardous explosive eruptions, which may be lurking undetected at many ocean island volcanoes.

VESIcal: 2. A Critical Approach to Volatile Solubility Modeling Using an Open‐Source Python3 Engine

“…Melt inclusion analyses have greatly advanced our understanding of the behavior of volatiles in volcanic systems (Hauri et al., 2002; Lowenstern, 2003; Métrich & Wallace, 2008; Roggensack, 2001; Sides et al., 2014a; Wallace et al., 1995). For example, melt inclusions provide insights into pre‐eruptive volatile contents (e.g., Hervig et al., 1989; Saal et al., 2002), and links between melt volatile contents and eruption styles (Lucic et al., 2016; Wieser et al., 2022). The strong pressure‐dependence on volatile solubility means that H 2 O and CO 2 contents within melt inclusions trapped from a volatile‐saturated magma can be used to determine the pressure at which the inclusion was sealed off (termed the saturation pressure or entrapment pressure).…”

“…Alternatively, saturation pressures could be plotted as histograms, cumulative density functions, or box/violin plots to assess clustering Wieser et al. (2022). Additionally, the ability to easily filter calculated saturation pressures by additional variables in python (e.g., host mineral content, amount of PEC, sample location, and stratigraphic height) will help to elucidate the record of the magmatic plumbing system preserved in different crystal populations.…”