Research Article

The tangled tale of Kīlauea’s 2018 eruption as told by geochemical monitoring

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Science  06 Dec 2019:
Vol. 366, Issue 6470, eaaz0147
DOI: 10.1126/science.aaz0147

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Caldera collapse and flank eruption

Real-time monitoring of volcanic eruptions involving caldera-forming events are rare (see the Perspective by Sigmundsson). Anderson et al. used several types of geophysical observations to track the caldera-forming collapse at the top of Kīlauea Volcano, Hawai'i, during the 2018 eruption. Gansecki et al. used near–real-time lava composition analysis to determine when magma shifted from highly viscous, slow-moving lava to low-viscosity, fast-moving lava. Patrick et al. used a range of geophysical tools to connect processes at the summit to lava rates coming out of far-away fissures. Together, the three studies improve caldera-collapse models and may help improve real-time hazard responses.

Science, this issue p. eaaz0147, p. eaay9070; p. eaaz1822; see also p. 1200

Structured Abstract

INTRODUCTION

Fissures sliced through Kīlauea Volcano’s lower east rift zone on 3 May 2018, eventually engulfing hundreds of structures in lava flows and triggering a collapse at the summit. During the eruption, we employed a rapid routine for geochemical analysis of lava, developed over 6 years of monitoring the prior continuous eruption at Kīlauea. The application of this routine elevated lava chemistry to a near real-time data stream in eruption monitoring, similar to seismic and geodetic data. It provided an unparalleled opportunity to understand changes in magma characteristics during a rapidly evolving eruptive crisis.

RATIONALE

Lava chemistry provides vital information on the underground sources of magma, eruptive conditions, temperature, and physical properties of lava flows. However, analytical techniques are typically slow, leaving chemical analysis of lava as a retrospective tool in the volcano sciences. We developed an analytical procedure to characterize the geochemistry of lava within a few hours of sample collection, allowing us to identify a specific suite of major and trace elements that track lava compositions and estimate lava temperatures through chemical geothermometers. This information was used to inform response teams of shifts in eruptive conditions.

RESULTS

The initial fissures erupted low volumes of chemically evolved basaltic lavas from 3 to 9 May, which were viscous and cool (~1110°C). On 13 May we detected less-evolved compositions and an increase in inferred lava temperatures (~1130°C). We informed science and response teams that the arrival of more fluid and voluminous lava was likely. Beginning 17 to 18 May, the lava from the primary fissures became increasingly less chemically evolved, hotter, and more fluid. By 28 May, activity focused on a single vent (fissure 8). This vent fed a massive outpouring of hotter (~1145°C) lava that continued for more than 2 months. During this stage, lavas became slightly hotter and lost the cargo of lower-temperature minerals that were initially abundant. The lava carried olivine crystals with unusually high MgO, indicative of the presence of much hotter magma (>1270°C) somewhere in the plumbing system. A second dominant olivine population formed in cooler magma similar to what was being erupted previously at the summit lava lake.

We also identified simultaneous, but more explosive, repetitive outbursts of andesite lava. This highly viscous and evolved composition, not previously known from Kīlauea, erupted at low temperatures (1060° to 1090°C) on a fissure offset from the other eruption fissures. The chemical and mineralogical fingerprint of this lava was also detected at other fissures several kilometers from the andesite vent.

CONCLUSION

Analysis of the data during the eruption revealed that at least three different sources of magma were feeding the eruption. The first two were the chemically evolved basalt of the initial fissures and the highly viscous andesite. Both are volumetrically minor sources that represent distinct pockets of old residual magma from Kīlauea’s east rift zone that evolved for more than 55 years, cooling and crystallizing at depth. The third and volumetrically more substantial source was less-evolved and hotter basalt of fissure 8. This source was similar in composition to the magma erupted at Kīlauea in the years before 2018 and was ultimately derived from the summit region. Draining and collapse of the summit by this voluminous eruption may have stirred up deeper, hotter parts of the summit magma system and sent mixed magma down the rift. By the final 20 days of the eruption, most magma stored within the active rift system had flushed out. Posteruption analyses done by traditional geochemical methods confirmed that the rapid-response routine produced comparable data and validated the models proposed during the active eruption. Our work has demonstrated that geochemical analyses of lava samples in near-real-time can yield critical information that enhances hazard assessments and risk mitigation during an eruption.

The 2018 lower east rift zone eruption of Kīlauea Volcano with inferred magma sources and pathways.

(A) Simplified model of Kīlauea’s magma system feeding the 2018 lower east rift zone eruption and locations of hypothesized magma end-members (b.s.l., below sea level). (B) Fluid basalt erupting from fissure 20 on 20 May 2018. (C) Fissure 17 erupting andesite more explosively 800 m away. Photos by U.S. Geological Survey.

Abstract

Changes in magma chemistry that affect eruptive behavior occur during many volcanic eruptions, but typical analytical techniques are too slow to contribute to hazard monitoring. We used rapid energy-dispersive x-ray fluorescence analysis to measure diagnostic elements in lava samples within a few hours of collection during the 2018 Kīlauea eruption. The geochemical data provided important information for field crews and civil authorities in advance of changing hazards during the eruption. The appearance of hotter magma was recognized several days before the onset of voluminous eruptions of fast-moving flows that destroyed hundreds of homes. We identified, in near real-time, interactions between older, colder, stored magma—including the unexpected eruption of andesite—and hotter magma delivered during dike emplacement.

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