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首页> 外文期刊>Journal of Volcanology and Geothermal Research >The run-out distance of large-scale pyroclastic density currents: A two-layer depth-averaged model
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The run-out distance of large-scale pyroclastic density currents: A two-layer depth-averaged model

机译：大规模热碎屑密度电流的跳动距离：两层深度平均模型

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摘要

We have developed a new two-layer pyroclastic density current (PDC) model that considers the effects of the entrainment and thermal expansion of ambient air in the upper dilute layer in order to investigate the dominant factors controlling the run-out distance of large-scale PDCs. Numerical simulations show a dilute current spreading radially from the collapsing eruption column edge and forming a thin, dense, basal current through particle settling; i.e., a two-layer PDC forms. Forward propagation of the two-layer PDC stops owing to lift-off of the dilute current and/or deposition of the dense current, and eventually the two-layer PDC converges to a steady state. Our parametric study classifies the flow patterns of steady-state two-layer PDCs into one of two flow regimes according to the relative magnitude of the run-out distances of the dilute and dense currents. This relative magnitude critically depends on the ratio of the deposition speed at the base of the dense current (D) to the speed of particles settling from the dilute current to the dense current (WO. The run-out distance of the whole two-layer PDC is determined by that of the dilute current when D/W-s is large (>= 4 x 10(-3)). Otherwise, when D/W-s is small (less than or similar to 4 x 10(-3)), the run-out distance of the dense basal current exceeds that of the dilute current; the former increases as D/W-s decreases. The run-out distance of the dilute current is too short to explain some of the long run-out distances of PDCs observed in the field (e.g., the 1991 Pinatubo and 2014 Kelud eruptions). It is suggested that the dense current traveling beyond the lift-off point of the parent dilute current plays a significant role in the emplacement of PDCs with such long run-out distances. (C) 2019 The Authors. Published by Elsevier B.V.
机译：我们研究了一种新的两层热碎屑密度电流（PDC）模型，该模型考虑了上层稀薄层中环境空气的夹带和热膨胀的影响，以便研究控制大规模跳动距离的主要因素PDC。数值模拟表明，稀电流从塌陷的喷发柱边缘沿径向扩散，并通过颗粒沉降形成稀薄，密集的基础电流。即两层PDC表单。由于稀薄电流的剥离和/或密集电流的沉积，两层PDC的正向传播停止，最终两层PDC收敛到稳定状态。我们的参数研究根据稀疏电流和密集电流的跳动距离的相对大小将稳态两层PDC的流型分类为两种流态之一。该相对大小严格取决于浓电流（D）底部的沉积速度与颗粒从稀电流到浓电流沉降的速度之比（WO。整个两层的跳动距离PDC由D / Ws大（> = 4 x 10（-3））时的稀电流决定；否则，当D / Ws小（小于或等于4 x 10（-3））时，致密基电流的跳动距离超过了稀释电流的跳动距离；前者随着D / Ws的减小而增加；稀释电流的跳动距离太短，无法解释PDC的一些长跳动距离在实地观察到（例如1991年的Pinatubo和2014年的Kelud喷发），这表明，在如此长的跳动中，超过母体稀薄流的提离点的稠密电流在安置PDC中起着重要作用。 （C）2019作者.Elsevier BV发布

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