Disrupt the upper or the lower conduit? The dual role of gas exsolution in the conduits of persistently active volcanoes
Disrupt the upper or the lower conduit? The dual role of gas exsolution in the conduits of persistently active volcanoes
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破坏上部或下部导管？
DOI：
10.1017/jfm.2022.346
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发表时间：
2022
影响因子：
3.7
通讯作者：
Suckale, Jenny
中科院分区：
文献类型：
--
作者：
Peng, Shirui;Picchi, Davide;Suckale, Jenny
许多火山在持续的被动除气过程中，而不是在喷发期间，释放出它们输送到大气中的很大一部分气体。为了在不喷发岩浆的情况下保持高的气体和热通量，火山导管内的流场必须与富气、浮力的岩浆上升和脱气、重岩浆下降大致平衡。在垂直管道中，这种交换流动采取核-环流的形式，在那里富含气体的岩浆形成一个被脱气岩浆环带包围的核心。核环流的流动动力学在流体力学中已经得到了广泛的研究，但大多是在材料性质不变的情况下进行的。我们的研究旨在增进我们对核环流对挥发性出溶的响应的理解--挥发性出溶是火山管道中一种简单但普遍存在的破坏，它改变了核心流体的密度和粘度。通过在广义交换流动条件下利用润滑近似推导出核心-环状界面的演化方程，我们发现系统对挥发分出溶的响应取决于管道流型。同一成核事件可能只在火山导管的上部、下部或两个部分引起流量调整。我们的结果强调，岩浆性质的热力学演化和火山导管流动是错综复杂的联系，这可能有助于理解观察到的持续脱气火山喷发行为的变异性。
Many volcanoes emit a significant portion of the gas they transport to the atmosphere during continual passive degassing rather than during eruptions. To maintain a high gas and thermal flux without erupting magma, the flow field in the volcanic conduit must be approximately balanced with gas-rich, buoyant magma ascending and degassed, heavy magma descending. In vertical conduits, this exchange flow takes the form of core–annular flow, where the gas-rich magma forms a core enclosed by an annulus of degassed magma. The flow dynamics of core–annular flow have been studied extensively in fluid dynamics, but mostly for constant material properties. Our study aims to advance our understanding of how core–annular flow responds to volatile exsolution – a simple, yet ubiquitous disruption in volcanic conduits, which alters both the density and the viscosity of the core fluid. By deriving an evolution equation for the core–annular interface based on a generalized exchange-flow condition using a lubrication approximation, we find that the response of the system to volatile exsolution depends on the conduit flow regime. The same nucleation event can lead to a flow adjustment only in the upper, only in the lower or in both portions of the volcanic conduit. Our results emphasize that the thermodynamic evolution of magma properties and volcanic conduit flow are intricately linked, which may help understand the observed variability of eruptive behaviour at persistently degassing volcanoes.
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