Coupling of turbulent and non-turbulent flow regimes within pyroclastic density currents
Coupling of turbulent and non-turbulent flow regimes within pyroclastic density currents
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DOI：
10.1038/ngeo2794
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发表时间：
2016-10-01
影响因子：
18.3
通讯作者：
Moebis, Anja
中科院分区：
文献类型：
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作者：
Breard, Eric C. P.;Lube, Gert;Moebis, Anja
火山爆发是最致命的，当火山碎屑密度流横扫景观，摧毁一切在其路径（1，2）。支撑这些危害的内部动力学无法直接观察到（3）。在这里，我们提出了一个定量的观点内火山碎屑密度电流合成其自然流动行为在大规模的实验。这些实验追踪了从初始到沉积的流动动力学，并可以解释真实世界沉积物的序列和演化。我们发现，在火山碎屑密度流内部，长期假设的非湍流底流和完全湍流的灰云区域（4，5）通过迄今为止未被认识到的中间湍流和浓度的中间区域连接在一起。中间区域以湍流的突然跳跃为界，在运动学上耦合了底流和灰云区域。在该区域内，气相和颗粒相之间的强烈反馈导致中尺度湍流团的形成。这些极其快速沉降的树枝状结构决定了火山碎屑密度流的内部分层和演化，并允许底流在跳动期间显著增长。我们的实验揭示了底流和火山灰云区域是如何动态相关的见解是有关火山灾害模型中的火山碎屑密度流行为的预测。
Volcanic eruptions are at their most deadly when pyroclastic density currents sweep across landscapes to devastate everything in their path(1,2). The internal dynamics underpinning these hazards cannot be directly observed(3). Here we present a quantitative view inside pyroclastic density currentsby synthesizing their natural flow behaviour in large-scale experiments. The experiments trace flow dynamics from initiation to deposition, and can explain the sequence and evolution of real-world deposits. We show that, inside pyroclastic density currents, the long-hypothesized non-turbulent underflow and fully turbulent ash-cloud regions(4,5) are linked through a hitherto unrecognized middle zone of intermediate turbulence and concentration. Bounded by abrupt jumps in turbulence, the middle zone couples underflow and ash-cloud regions kinematically. Inside this zone, strong feedback between gas and particle phases leads to the formation of mesoscale turbulence clusters. These extremely fast-settling dendritic structures dictate the internal stratification and evolution of pyroclastic density currents and allow the underflows to grow significantly during runout. Our experiments reveal how the underflow and ash-cloud regions are dynamically related-insights that are relevant to the forecasting of pyroclastic density current behaviour in volcanic hazard models.