Gas slug ascent in a stratified magma:implications of flow organisation and instability for Strombolian eruption dynamics
Gas slug ascent in a stratified magma:implications of flow organisation and instability for Strombolian eruption dynamics
复制标题
层状岩浆中的气段塞上升：流动组织和不稳定性对斯特龙博利式喷发动力学的影响
DOI：
10.1016/j.epsl.2015.12.028
复制
发表时间：
2016
影响因子：
5.3
通讯作者：
S. Lane
中科院分区：
文献类型：
--
作者：
A. Capponi;M. James;S. Lane
气体段塞在均匀的低粘度岩浆中上升和破裂的典型Strombolian范式不能解释最近由现场测量、结构和地球化学分析揭示的喷发动力学的复杂细节。有证据表明，在斯特隆波利亚型火山的管道顶部存在高粘度岩浆，起到了堵塞物的作用。在这里，新的实验详细描述了段塞在管道内流变层状岩浆的上升和破裂过程中形成的流动结构范围。完全充满高粘度或低粘度液体支架的管道端部场景有三种主要的流动配置：(1)一个足够大的塞，可以完全容纳上升的气段塞；(2)一种能够容纳由气体膨胀驱动的低粘度液体侵入的塞，但不能容纳所有塞段塞体积，因此塞段塞爆发时，塞头在塞内，而塞的底部仍在低粘度液体中；(3)气体膨胀足以驱动低粘度液体通过桥塞侵入，在低粘度层的段塞破裂动态放置在桥塞上方。通过新的实验验证的一维模型和三维计算流体动力学模拟，我们证明了相同的流动构型在火山尺度上是可行的。应用Stromboli模型，研究结果表明，控制两种构型转换的关键参数是气体体积、桥塞厚度和桥塞粘度。确定的流动过程包括管道的有效动态变窄和变宽、岩浆膜下降的不稳定性、管道的短暂部分和完全堵塞以及段塞破坏。这些复杂性影响了喷发动力学和活力，促进了岩浆的混合，导致了气体的脉动释放。
The canonical Strombolian paradigm of a gas slug ascending and bursting in a homogeneous low-viscosity magma cannot explain the complex details in eruptive dynamics recently revealed by field measurements and textural and geochemical analyses. Evidence points to the existence of high-viscosity magma at the top of the conduit of Strombolian-type volcanoes, acting as a plug. Here, new experiments detail the range of flow configurations that develop during the ascent and burst of a slug through rheologically stratified magma within a conduit. End-member scenarios of a tube fully filled with either high- or low-viscosity liquid bracket three main flow configurations: (1) a plug sufficiently large to fully accommodate an ascending gas slug; (2) A plug that can accommodate the intrusion of low-viscosity liquid driven by the gas expansion, but not all the slug volume, so the slug bursts with the nose in the plug whilst the base is still in the low-viscosity liquid; (3) Gas expansion is sufficient to drive the intrusion of low-viscosity liquid through the plug, with the slug bursting in the low-viscosity layer emplaced dynamically above the plug. We show that the same flow configurations are viable at volcanic-scale through a new experimentally-validated 1D model and 3D computational fluid dynamic simulations. Applied to Stromboli, our results demonstrate that the key parameters controlling the transition between each configuration are gas volume, plug thickness and plug viscosity. The flow processes identified include effective dynamic narrowing and widening of the conduit, instabilities within the falling magma film, transient partial and complete blockage of the conduit, and slug disruption. These complexities influence eruption dynamics and vigour, promoting magma mingling and resulting in pulsatory release of gas.