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首页> 外文期刊>Journal of Volcanology and Geothermal Research >A two-layer model for the evolution and propagation of dense and dilute regions of pyroclastic currents
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A two-layer model for the evolution and propagation of dense and dilute regions of pyroclastic currents

机译：火山碎屑流密集和稀薄区域的演化和传播的两层模型

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摘要

We present calculations of a simplified two-layer pyroclastic flow model, which incorporates different physics to represent the dense and dilute regions of column collapse pyroclastic density currents. The two layers evolve separately, but are coupled through mass exchange as suspended ash in the dilute cloud settles into the underlying dense basal layer. The runout distance of the upper dilute current and the associated runout time are found to increase with increasing initial column height and decreasing particle size. Likewise steeper slopes increase the propagation velocity and thus the runout distance. The independent runout distance of the basal flow exhibits opposite behaviour to that of the parent dilute current, increasing with decreasing initial column height and increasing particle size. Observed runout distances can be calculated for basal flows using a Coulomb friction law, but deposit morphology is not well reproduced and is more realistic when an empirical slope-dependent sedimentation rate is included. Dominant flow behaviour is controlled by the rate of mass transfer from the parent suspension current into the dense underflow. Tall column collapses, which contain fine-grained particles, transfer their mass slowly to the dense basal flow and are well described by dilute cloud assumptions. However, for short columns containing coarse grains, the particulate mass is rapidly transferred from the collapsing dilute current into the basal flow. The bulk of the pyroclastic current material propagates as a concentrated suspension for the majority of its travel distance and is better described by the physics of granular avalanches.
机译：我们介绍了简化的两层火山碎屑流模型的计算，该模型结合了不同的物理原理来表示柱塌陷火山碎屑密度流的密集和稀薄区域。这两层分别演化，但随着稀云中的悬浮灰分沉降到下面的致密基底层中而通过质量交换耦合。发现较高的稀电流的跳动距离和相关的跳动时间随着初始柱高的增加和粒径的减小而增加。同样，更陡的斜坡会增加传播速度，从而增加跳动距离。基流的独立跳动距离表现出与母体稀流相反的行为，随着初始柱高的减小和粒径的增加而增加。可以使用库仑摩擦定律计算基流的观测到的跳动距离，但是如果包括基于经验的坡度相关的沉降速率，则沉积物形态不能很好地再现，并且更现实。主导流动行为由母体悬浮液流向致密底流的质量转移速率控制。高塔倒塌，其中包含细颗粒，将其质量缓慢转移到稠密的基流中，并通过稀薄的云假设很好地描述。但是，对于包含粗粒的短柱，颗粒物质会从坍塌的稀流中迅速转移到基流中。大部分的火山碎屑流物质在其大部分传播距离中都以浓缩悬浮液的形式传播，并且可以通过颗粒雪崩的物理学更好地描述。

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  • 来源
    《Journal of Volcanology and Geothermal Research》 |2010年第4期|365-378|共14页
  • 作者

    E.E. Doyle; A.J. Hogg; H.M. Mader; R.S.J. Sparks;

  • 作者单位

    Soil and Earth Sciences Group, Institute of Natural Resources, PN 432, Massey University, Private Bag 11 222, Palmerston North, New Zealand Centre for Environmental and Geophysical Flows, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ, UK;

    Centre for Environmental and Geophysical Flows, School of Mathematics, University of Bristol, University Walk, Bristol, BS8 1TW, UK;

    Centre for Environmental and Geophysical Flows, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ, UK;

    Centre for Environmental and Geophysical Flows, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ, UK;

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  • 正文语种 eng
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  • 关键词

    pyroclastic flow; numerical model; dense basal flow; dilute current; sedimentation; deposit;

    机译：火山碎屑流数值模型密集的基流稀释电流沉降;存款;

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