In basaltic eruptions, bubbles move freely and collide within a volcanic conduit, leading to frequent bubble coalescence. Understanding the dynamics of buoyancy-driven coalescence of bubbles is crucial for predicting the explosivity of basaltic eruptions. We examine the evolution of the bubble volume distribution while considering buoyancy-driven coalescence and expansion due to decompression. We find that, at lower decompression rates, the bubble volume distribution $n(v,t)$ rapidly evolves into a power-law distribution with an exponent of approximately $-2$ as $n(v,t)\propto v^{-2}$. This suggests that, in basaltic magma, the repeated coalescence of bubbles rapidly forms large bubbles within 45 min to 3 days. We then examine the occurrence of eruption styles, specifically Strombolian or Hawaiian, under the assumption that the bursts of slugs, produced from bubble coalescence within the conduit, trigger Strombolian eruptions. Consequently, we identify a critical condition for the transition between eruption styles in terms of the ascent velocity of magma. This critical ascent velocity is consistent with the observed transitions between Strombolian and Hawaiian eruptions at Izu-Oshima and Kilauea.

中文翻译：

---

浮力驱动的气泡快速聚结：对玄武岩喷发中蛞蝓形成的影响


在玄武岩喷发中，气泡在火山管道内自由移动并碰撞，导致气泡频繁聚结。了解浮力驱动的气泡聚结动力学对于预测玄武岩喷发的爆炸性至关重要。我们研究了气泡体积分布的演变，同时考虑了由于减压引起的浮力驱动的聚结和膨胀。我们发现，在较低的减压速率下，气泡体积分布 $n（v，t）$ 迅速演变为幂律分布，指数约为 $-2$，为 $n（v，t）\propto v^{-2}$.这表明，在玄武岩岩浆中，气泡的反复聚结会在 45 分钟到 3 天内迅速形成大气泡。然后，我们研究了喷发类型的发生，特别是 Strombolian 或 Hawaiian，假设管道内气泡聚结产生的蛞蝓爆发会触发 Strombolian 喷发。因此，我们确定了岩浆上升速度方面喷发类型之间过渡的关键条件。这种临界上升速度与在伊豆大岛和基拉韦厄观察到的 Strombolian 和 Hawaiian 喷发之间的过渡一致。