Explosivity of basaltic lava fountains is controlled by magma rheology, ascent rate and outgassing
Explosivity of basaltic lava fountains is controlled by magma rheology, ascent rate and outgassing
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DOI：
10.1016/j.epsl.2020.116658
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发表时间：
2021-01-01
影响因子：
5.3
通讯作者：
Mader, H. M.
中科院分区：
文献类型：
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作者：
La Spina, G.;Arzilli, F.;Mader, H. M.
产生火山碎屑的爆炸性火山爆发和产生熔岩的喷涌性火山爆发之间的二分法是由岩浆上升过程中是否存在碎裂来定义的。对于熔岩喷泉来说，这种区别是不清楚的，因为上升的岩浆中的液相可能一直持续到喷口，在喷泉中破碎，然后在沉积上重新焊接，形成流变熔岩流。本文以基拉韦厄火山和埃特纳火山为例，采用数值模型对玄武岩喷发方式进行控制。根据我们的研究结果，我们认为熔岩喷涌是一种独特的喷发方式，与喷涌式和爆发性喷发风格不同，它是在岩浆迅速上升并在喷口上方破碎而不是在管道内产生的。基拉韦厄火山和埃特纳火山的敏感性分析表明，当气泡岩浆的雷诺数大于0.1，体积粘度小于10(6)Pas，气体与熔体耦合良好时，会出现高熔岩喷泉（> ~ 50 m）。对于高黏度玄武岩（典型的埃特纳火山），预测爆发（普林尼期和次普林尼期）的参数空间范围很广，但对于低黏度玄武岩（典型的基拉韦厄火山），预测爆发的参数空间范围要窄得多。数值结果还表明，供给高熔岩喷泉的岩浆比供给爆炸性喷发的岩浆上升得更快，因为它的粘度更低。对于基拉韦厄火山的案例研究，上升速度的减弱预计会产生一个从高喷泉到弱喷泉，到最终渗出的渐进演变；而在埃特纳火山的案例研究中，参数值的微小变化会导致爆发活动的转变，这表明喷发的转变可能在没有任何预警的情况下发生。(C) 2020作者。Elsevier B.V.出版
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 similar to 0.1, the bulk viscosity is less than 10(6) Pas, 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. (C) 2020 The Authors. Published by Elsevier B.V.