TY - JOUR
T1 - Explosivity of basaltic lava fountains is controlled by magma rheology, ascent rate and outgassing
AU - La Spina, G.
AU - Arzilli, F.
AU - Llewellin, E. W.
AU - Burton, M. R.
AU - Clarke, A. B.
AU - de' Michieli Vitturi, M.
AU - Polacci, M.
AU - Hartley, M. E.
AU - Di Genova, D.
AU - Mader, H. M.
N1 - Funding Information:
Sensitivity analyses were performed on the ARCHER National Supercomputing Service. The research leading to these results has received funding from the RCUK NERC DisEqm project ( NE/N018575/1 ). ABC's participation was funded through the US NSF ( EAR-1642569 ). We are really grateful to Daniele Andronico (INGV) and Ben Gaddis (USGS Hawaiian Volcano Observatory) for their assistance on finding pictures of lava fountaining activities on Etna and Kilauea. Finally, we gratefully acknowledge two anonymous reviewers for their useful and constructive comments, which improved this manuscript.
Publisher Copyright:
© 2020 The Authors
PY - 2021/1/1
Y1 - 2021/1/1
N2 - The dichotomy between explosive volcanic eruptions, which produce pyroclasts, and effusive eruptions, which produce lava, is defined by the presence or absence of fragmentation during magma ascent. For lava fountains the distinction is unclear, since the liquid phase in the rising magma may remain continuous to the vent, fragment in the fountain, then re-weld on deposition to feed rheomorphic lava flows. Here we use a numerical model to constrain the controls on basaltic eruption style, using Kilauea and Etna as case studies. Based on our results, we propose that lava fountaining is a distinct style, separate from effusive and explosive eruption styles, that is produced when magma ascends rapidly and fragments above the vent, rather than within the conduit. Sensitivity analyses of Kilauea and Etna case studies show that high lava fountains (>50 m high) occur when the Reynolds number of the bubbly magma is greater than ∼0.1, the bulk viscosity is less than 106Pas, and the gas is well-coupled to the melt. Explosive eruptions (Plinian and sub-Plinian) are predicted over a wide region of parameter space for higher viscosity basalts, typical of Etna, but over a much narrower region of parameter space for lower viscosity basalts, typical of Kilauea. Numerical results show also that the magma that feeds high lava fountains ascends more rapidly than the magma that feeds explosive eruptions, owing to its lower viscosity. For the Kilauea case study, waning ascent velocity is predicted to produce a progressive evolution from high to weak fountaining, to ultimate effusion; whereas for the Etna case study, small changes in parameter values lead to transitions to and from explosive activity, suggesting that eruption transitions may occur with little warning.
AB - The dichotomy between explosive volcanic eruptions, which produce pyroclasts, and effusive eruptions, which produce lava, is defined by the presence or absence of fragmentation during magma ascent. For lava fountains the distinction is unclear, since the liquid phase in the rising magma may remain continuous to the vent, fragment in the fountain, then re-weld on deposition to feed rheomorphic lava flows. Here we use a numerical model to constrain the controls on basaltic eruption style, using Kilauea and Etna as case studies. Based on our results, we propose that lava fountaining is a distinct style, separate from effusive and explosive eruption styles, that is produced when magma ascends rapidly and fragments above the vent, rather than within the conduit. Sensitivity analyses of Kilauea and Etna case studies show that high lava fountains (>50 m high) occur when the Reynolds number of the bubbly magma is greater than ∼0.1, the bulk viscosity is less than 106Pas, and the gas is well-coupled to the melt. Explosive eruptions (Plinian and sub-Plinian) are predicted over a wide region of parameter space for higher viscosity basalts, typical of Etna, but over a much narrower region of parameter space for lower viscosity basalts, typical of Kilauea. Numerical results show also that the magma that feeds high lava fountains ascends more rapidly than the magma that feeds explosive eruptions, owing to its lower viscosity. For the Kilauea case study, waning ascent velocity is predicted to produce a progressive evolution from high to weak fountaining, to ultimate effusion; whereas for the Etna case study, small changes in parameter values lead to transitions to and from explosive activity, suggesting that eruption transitions may occur with little warning.
KW - basalt
KW - effusive eruption
KW - explosive eruption
KW - fragmentation
KW - lava fountain
KW - magma ascent
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U2 - 10.1016/j.epsl.2020.116658
DO - 10.1016/j.epsl.2020.116658
M3 - Article
AN - SCOPUS:85096379119
SN - 0012-821X
VL - 553
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
M1 - 116658
ER -