Explosive basaltic eruptions pose significant threats to local communities, regional infrastructures and international airspace. They produce tephra plumes that are often associated with a lava fountain, complicating their dynamics. Consequently, source parameters cannot be easily constrained using traditional formulations. Particularly, mass flow rates (MFRs) derived from height observations frequently differ from field deposit-derived MFRs. Here, we investigate this discrepancy using a novel integral plume model that explicitly accounts for a lava fountain, which is represented as a hot, coarse-grained inner plume co-flowing with a finer-grained outer plume. The new model shows that a plume associated with a lava fountain has higher variability in rise height than a standard plume for the same initial MFR depending on initial conditions. The initial grain-size distribution and the relative size of the lava fountain compared to the surrounding plume are primary controls on the final plume height as they determine the strength of coupling between the two plumes. We apply the new model to the August 29, 2011 paroxysmal eruption of Mount Etna, Italy. The modeled MFR profile indicates that the field-derived MFR does not correspond to that at the vent, but rather the MFR just above the lava fountain top. High fallout from the lava fountain results in much of the erupted solid material not reaching the top of the plume. This material deposits to form the proximal cone rather than dispersing in the atmosphere. With our novel model, discrepancies between the two types of observation-derived MFR can be investigated and understood.

中文翻译：

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与熔岩喷泉耦合的浮力 Tephra 羽流模型，适用于 2011 年 8 月 29 日意大利埃特纳火山的阵发性喷发

爆炸性玄武岩喷发对当地社区、区域基础设施和国际空域构成重大威胁。它们产生通常与熔岩喷泉相关的火山灰羽流，使它们的动态复杂化。因此，使用传统公式无法轻易限制源参数。特别是，从高度观测得出的质量流量 (MFR) 经常不同于现场沉积物得出的 MFR。在这里，我们使用一种新颖的整体羽流模型来研究这种差异，该模型明确解释了熔岩喷泉，其表示为热的粗粒内羽流与细粒外羽流共同流动。新模型表明，对于相同的初始 MFR，与熔岩喷泉相关的羽流在上升高度上的变异性高于标准羽流，具体取决于初始条件。初始粒度分布和熔岩喷泉与周围羽流相比的相对大小是最终羽流高度的主要控制因素，因为它们决定了两个羽流之间的耦合强度。我们将新模型应用于 2011 年 8 月 29 日意大利埃特纳火山的阵发性喷发。建模的 MFR 剖面表明，现场导出的 MFR 与喷口处的 MFR 不对应，而是熔岩喷泉顶部上方的 MFR。熔岩喷泉的大量沉降导致大部分喷发的固体物质没有到达羽流的顶部。这种材料沉积形成近端锥体，而不是分散在大气中。使用我们的新模型，可以调查和理解两种类型的观察得出的 MFR 之间的差异。