Fragmentation mechanisms associated with explosive lava-water interactions in a lacustrine environment
Fragmentation mechanisms associated with explosive lava-water interactions in a lacustrine environment
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DOI：
10.1007/s00445-016-1087-3
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发表时间：
2017-01-01
影响因子：
3.5
通讯作者：
Hamilton, Christopher W.
中科院分区：
文献类型：
--
作者：
Fitch, Erin P.;Fagents, Sarah A.;Hamilton, Christopher W.
当部分喷出的熔岩与外部水发生爆炸性相互作用时，就形成了无根的圆锥体。爆炸代表了一个端员系统，它可以在没有放气导致岩浆破碎的情况下解释爆炸岩浆-水相互作用的机制。在无根爆炸中产生的细碎喷射物(即火山灰)的比例可能对爆炸的能量有很大贡献，即使相对于较粗的喷射物来说，火山灰的体积很小。实验室实验表明，熔水混合程度和能量释放与块状颗粒的丰度成正比，块状颗粒被脆性解体破碎，有效地为系统提供热能。为了约束无根爆炸活动的机制和动力学，我们通过对与湖(湖)盆地环境中的泡状熔岩流有关的无根特弗拉的形态、结构和密度分析，评估了无根爆炸活动的性质和模式以及喷发特征。我们观察到平均粒度与块状(负幂规律趋势)和流体(正对数)的各种大小的Tephra碎屑的质量百分比之间有很强的相关性。我们将这些趋势解释为与尺度相关的破碎行为，这是由于流体动力破碎在更细的尺度上发生时效率降低，特别是在火山灰粒度范围内。此外，所有被分析的床层都含有细小的火山灰大小的块状和苔藓状碎屑，被认为是热能到机械能的高传递率的诊断，这是熔融燃料-冷却剂相互作用的特征。这些结果与最近的无根圆锥形成模型、先前的碎裂理论和大规模的实验室实验相一致，因此为未来的实验和建模工作提供了一个基于现场的模拟。
Rootless cones form when partially outgassed lava interacts explosively with external water. The explosions represent an end-member system that can elucidate mechanisms of explosive magma-water interactions in the absence of magmatic fragmentation induced by outgassing. The proportion of finely fragmented ejecta (i.e., ash), generated in rootless explosions, may contribute significantly to the energy of the explosion even if the ash volume is small relative to coarser ejecta. Laboratory experiments indicate that the degree of melt-water mixing and energy release are proportional to the abundance of blocky grains, fragmented by brittle disintegration, which effectively contribute thermal energy to the system. To constrain the mechanisms and dynamics of rootless explosive activity, we assess the nature and modes of fragmentation and ejecta characteristics through morphological, textural, and density analysis of rootless tephra associated with a pahoehoe lava flow in a lacustrine (lake basin) environment. We observe strong correlations between the mean grain size and the mass percentage of both blocky (negative power law trend) and fluidal (positive logarithmic) tephra clasts of all sizes. We interpret these trends as scale-dependent fragmentation behavior due to the decreasing efficacy of hydrodynamic fragmentation as it occurs over finer scales, especially over the ash size range. Additionally, all analyzed beds contain fine ash-sized blocky and mossy clasts, which are thought to be diagnostic of a high transfer rate of thermal to mechanical energy, characteristic of molten fuel-coolant interactions. These results agree with a recent model of rootless cone formation, prior fragmentation theory, and scaled laboratory experiments and therefore provide a field-based analog for future experimental and modeling efforts.