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Publication - Professor Heidy Mader

    Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallisation


    Arzilli, F, La Spina, G, Burton, M, Polacci, M, Le Gall, N, Hartley, M, Di Genova, D, Cai, B, Vo, N, Bamber, E, Nonni, S, Atwood, R, Llewellin, E, Brooker, R, Mader, H & Lee, P, 2019, ‘Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallisation’. Nature Geoscience.


    Basaltic eruptions are the most common form of volcanism on Earth and planetary bodies. The low viscosity of basaltic magmas inhibits fragmentation, favouring effusive and lava-fountaining activity, yet highly explosive, hazardous basaltic eruptions do occur. The processes that promote fragmentation of basaltic magma remain unclear, and are subject to debate. Here, we use a numerical conduit model to show that rapid ascent of magma during explosive eruption produces large undercooling. Novel in situ experiments reveal that undercooling drives exceptionally rapid (~minutes) crystallisation, inducing a step-change in viscosity that triggers magma fragmentation. Experimentally-produced textures are consistent with products of basaltic Plinian eruptions. We apply the numerical model to investigate basaltic magma fragmentation over a wide parameter space and find that all basaltic volcanoes have the potential to produce highly explosive eruptions. The critical requirements are initial magma temperatures lower than 1100 °C, in order to reach a syn-eruptive crystal content of > 30 vol.%, and thus a magma viscosity ≥ 105 Pa s, which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas. Our study provides both a demonstration and explanation of the processes that drive basaltic Plinian eruptions, revealing how typically effusive basaltic volcanoes can produce unexpected highly explosive, and hazardous, eruptions.

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