Explosive Activity on Kīlauea's Lower East Rift Zone Fueled by a Volatile‐Rich, Dacitic Melt

Penny E Wieser,Marie Edmonds,Eimf Eimf,Cheryl Gansecki,Paula Antoshechkina,Frances E Jenner,Frank Trusdell,John Maclennan,Barbara Kunz,R L Lee

doi:10.1029/2021gc010046

Abstract

AbstractMagmas with matrix glass compositions ranging from basalt to dacite erupted from a series of 24 fissures in the first 2 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, and 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 inclusion 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 and 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.

Highlights

The main shield-building stage of volcanism at ocean island volcanoes fed by high melt fluxes from mantle plume melting (e.g., Hawai’i, Galápagos, Réunion) is characterized by the eruption of basaltic lava flows, spatter, and occasional energetic lava fountains (Macdonald, 1962; Swanson et al, 1979)
Melt inclusion and matrix glass Cl and F concentrations increase with decreasing melt MgO contents, with the most volatile-rich dacitic melt inclusions erupted at Fissure 17 (F17) having Cl and F concentrations of ~1000 ppm (3-5 times higher than observed in melt inclusions erupted in phase 3; Fig. 3a-b)
The upper limit of melt inclusion H2O contents increases with fractional crystallization, reaching 1 wt% in the early Phase 1 lavas with ~4 wt% MgO, and up to 2 wt% in melt inclusions erupted at F17 with 0.5-1 wt% MgO (Fig. 3d)

Summary

Introduction

The main shield-building stage of volcanism at ocean island volcanoes fed by high melt fluxes from mantle plume melting (e.g., Hawai’i, Galápagos, Réunion) is characterized by the eruption of basaltic lava flows, spatter, and occasional energetic lava fountains (Macdonald, 1962; Swanson et al, 1979). On a number of occasions at Kīlauea Volcano, HI, erupted basaltic lava has pooled within existing pit craters, undergoing extensive fractional crystallization at near atmospheric pressures (e.g., 1959 Kīlauea Iki lava lake, 1963 Alae lava lake, 1965 Makaopuhi Crater; Helz, 1980; Wright et al, 1976). It is becoming increasingly apparent that andesitic to rhyolitic melts analogous to those formed in surface lava lakes may co-exist with basaltic melts at depth within a range of volcanic plumbing systems, even if these more silicic compositions are poorly represented in erupted rock compositions (Stock et al, 2020). Examination of lava and tephra samples from the 2015 eruption of Wolf Volcano and the 1968 eruption of Fernandina in the Galapagos identified plagioclase crystals whose compositions indicate that they grew from basaltic trachy-andesite and trachy-andesitic melts (Stock et al, 2020)

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