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Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallisation.

Arzilli, F. and La Spina, G. and Burton, M. and Polacci, M. and Le Gall, N. and Hartley, M. and Di Genova, D. and Cai, B. and Vo, N. and Bamber, E. and Nonni, S. and Atwood, R. and Llewellin, E. and Brooker, R. and Mader, H. and Lee, P. (2019) 'Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallisation.', Geoscience., 12 . pp. 1023-1028.


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.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Date accepted:11 September 2019
Date deposited:02 October 2019
Date of first online publication:21 October 2019
Date first made open access:21 April 2020

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