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Earthquakes indicated magma viscosity during Kīlauea’s 2018 eruption


Magma viscosity strongly controls the style (for example, explosive versus effusive) of a volcanic eruption and thus its hazard potential, but can only be measured during or after an eruption. The identification of precursors indicative of magma viscosity would enable forecasting of the eruption style and the scale of associated hazards1. The unanticipated May 2018 rift intrusion and eruption of Kīlauea Volcano, Hawai‘i2 displayed exceptional chemical and thermal variability in erupted lavas, leading to unpredictable effusion rates and explosivity. Here, using an integrated analysis of seismicity and magma rheology, we show that the orientation of fault-plane solutions (which indicate a fault’s orientation and sense of movement) for earthquakes preceding and accompanying the 2018 eruption indicate a 90-degree local stress-field rotation from background, a phenomenon previously observed only at high-viscosity eruptions3, and never before at Kīlauea4,5,6,7,8. Experimentally obtained viscosities for 2018 products and earlier lavas from the Pu‘u ‘Ō‘ō vents tightly constrain the viscosity threshold required for local stress-field reorientation. We argue that rotated fault-plane solutions in earthquake swarms at Kīlauea and other volcanoes worldwide provide an early indication that unrest involves magma of heightened viscosity, and thus real-time monitoring of the orientations of fault-plane solutions could provide critical information about the style of an impending eruption. Furthermore, our results provide insight into the fundamental nature of coupled failure and flow in complex multiphase systems.

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Fig. 1: Overview of Kīlauea Volcano, HV seismic network (inverted orange triangles), and locations/FPS showing fault orientation and sense of slip (beachball symbols) for 11 background-period earthquakes in LERZ.
Fig. 2: Map views of eruption FPS.
Fig. 3: Time−longitude plots of recorded earthquakes and FPS at Kīlauea Volcano during the study period.
Fig. 4: Bulk viscosity of Kīlauea 2018 and Pu‘u ‘Ō‘ō (PO) eruptive products.

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Data availability

Continuous seismic waveform data (network codes HV (, Z6 (, and 4S ( are available through the IRIS Data Management Center. A catalogue of located earthquakes is available through the USGS National Earthquake Information Center ( Source data are provided with this paper.


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We thank H. Dietterich, F. Pollitz, and F. Sigmundsson for constructive comments that improved the quality of this manuscript. A.S. acknowledges the support of the Alexander von Humboldt Postdoctoral Fellowship. D.B.D. was supported by ERC 2018 ADV Grant 834225 (EAVESDROP). B.F.H. acknowledges funding by NSF EAR 1829188 and USGS Disaster Supplemental Research funding.

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Authors and Affiliations



D.C.R. and B.R.S. calculated earthquake locations and FPS. D.C.R. conducted Coulomb stress modelling. A.S. and D.B.D. conducted viscosity experiments and modelling. B.F.H. conducted sample collection. D.C.R. led the interpretation and writing of the manuscript, and all co-authors contributed to the interpretation and writing of the manuscript.

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Correspondence to D. C. Roman.

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Peer review information Nature thanks Fred Pollitz and Freysteinn Sigmundsson for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Table 1 Experimentally determined and modelled viscosities for Kīlauea 2018 and Pu‘u ‘Ō‘ō samples

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Roman, D.C., Soldati, A., Dingwell, D.B. et al. Earthquakes indicated magma viscosity during Kīlauea’s 2018 eruption. Nature 592, 237–241 (2021).

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