Abstract 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 10 6 Pa s , 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.

中文翻译：

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玄武岩熔岩喷泉的爆炸性受岩浆流变学、上升速率和释气控制

摘要 产生火山碎屑的爆炸性火山喷发和产生熔岩的喷发喷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，区别尚不清楚，因为上升的岩浆中的液相可能保持连续到喷口，在喷泉中破碎，然后在沉积时重新焊接以供给流变熔岩流。在这里，我们使用数值模型来约束对玄武岩喷发类型的控制，以基拉韦厄和埃特纳火山作为案例研究。根据我们的结果，我们提出熔岩喷泉是一种独特的风格，与喷发和爆炸性喷发风格不同，当岩浆快速上升并在喷口上方碎裂时产生，而不是在管道内。Kilauea 和 Etna 案例研究的敏感性分析表明，当气泡岩浆的雷诺数大于~0.1、体积粘度小于 10 6 Pa s 且气体良好时，会出现高熔岩喷泉（> 50 m 高） -耦合到熔体。预测爆发性喷发（普林阶和亚普林阶）是在埃特纳火山典型的较高粘度玄武岩的宽广参数空间区域内，但在基拉韦厄火山典型的较低粘度玄武岩的参数空间窄得多的区域内预测。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，因为它的粘度较低。对于基拉韦厄案例研究，预计上升速度下降会产生从高喷泉到弱喷泉，再到最终积液的渐进式演变；而对于埃特纳火山案例研究，