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Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization


Basaltic eruptions are the most common form of volcanism on Earth and planetary bodies. The low viscosity of basaltic magmas inhibits fragmentation, which favours effusive and lava-fountaining activity, yet highly explosive, hazardous basaltic eruptions occur. The processes that promote fragmentation of basaltic magma remain unclear and are subject to debate. Here we used a numerical conduit model to show that a rapid magma ascent during explosive eruptions produces a large undercooling. In situ experiments revealed that undercooling drives exceptionally rapid (in minutes) crystallization, which induces a step change in viscosity that triggers magma fragmentation. The experimentally produced textures are consistent with basaltic Plinian eruption products. We applied a numerical model to investigate basaltic magma fragmentation over a wide parameter space and found that all basaltic volcanoes have the potential to produce highly explosive eruptions. The critical requirements are initial magma temperatures lower than 1,100 °C to reach a syn-eruptive crystal content of over 30 vol%, and thus a magma viscosity around 105 Pa s, which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas. These temperature, crystal content and viscosity requirements reveal how typically effusive basaltic volcanoes can produce unexpected highly explosive and hazardous eruptions.

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Fig. 1: Crystallization through time during experiment ET1150.
Fig. 2: Plagioclase crystal morphology.
Fig. 3: Model results during magma ascent.
Fig. 4: Sensitivity analyses.

Data availability

The authors declare that the experimental and analytical data supporting the findings of this study are available within the article and its Supplementary Information. The numerical data, generated by the code, are available from the corresponding author upon request.

Code availability

The code that supports the findings and of this study and used to generate Figs. 3 and 4 is available from the corresponding author upon request.


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The research leading to these results has received funding from the RCUK NERC DisEqm project (NE/N018575/1) and (NE/M013561/1). The beamtime on I12 was provided by Diamond Light Source (EE16188-1) and laboratory space by the Research Complex at Harwell. Sensitivity analyses were performed on the ARCHER National Supercomputing Service.

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M.P., F.A., M.R.B. and P.D.L. conceived the research project. F.A., M.P., G.L.S., N.L.G., B.C., M.E.H., D.D.G., N.T.V., S.N., R.A., E.W.L., P.D.L., H.M.M. and M.R.B. contributed to the beamline experiments. F.A. collected the volcanic rocks for the starting material. D.D.G., H.M.M. and R.A.B. prepared the starting material. F.A., M.P., G.L.S. and N.T.V. performed image reconstruction. F.A. and M.P. performed image processing. F.A. performed the image segmentation and analysis. G.L.S. performed numerical simulations using the conduit model. R.A.B. and F.A. performed the ex situ decompression experiments. F.A. and M.E.H. performed chemical analysis. E.C.B., F.A. and G.L.S. collected samples of the Etna 122 bc Plinian eruption. E.C.B. and F.A. acquired and analysed the BSE images of Etna 122 bc Plinian eruption samples. F.A., G.L.S., M.R.B., M.P. and E.C.B. wrote the manuscript, with contributions from all the authors.

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Correspondence to Fabio Arzilli.

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Supplementary Figs. 1–6 and Tables 1–4.

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Arzilli, F., La Spina, G., Burton, M.R. et al. Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization. Nat. Geosci. 12, 1023–1028 (2019).

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