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Self-organization and run-out behaviour of geophysical mass flows

地球物理质量流的自组织和运行行为

基本信息

批准号：
NE/K003011/1
负责人：
Nico Gray
金额：
$ 48.4万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2013
资助国家：
英国
起止时间：
2013 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FK003011%2F1
关键词：
Self organization run out behaviour

项目摘要

It is vitally important to anticipate the run-out behaviour of geophysical mass flows and thus anticipate their impact area and peak destructive power, to develop effective strategies to improve the safety of "at risk" populations throughout the world. Geophysical mass flows encompass a wide range of natural hazards including snow avalanches, debris-flows, pyroclastic flows and lahars. They are all examples of either wet or dry granular flows in which "large" particles segregate towards the surface, where the velocity is greatest, and are preferentially transported towards flow fronts. Here they may be over-run, rise up by segregation, and be recirculated to produce bouldery flow fronts. These tend to be more resistive to motion than the finer grained interior, either because the grains are rougher or because in debris- and pyroclastic flows they dissipate the internal pore pressures that confer mobility. These segregation-mobility feedback effects can lead to the development of damaging high-mass-concentration surge fronts and can cause spreading flows to spontaneously develop lobes and leveed channels that transfer the mass readily for long distances (run-out). Such self-organization has important implications for hazard assessment and risk mitigation, because large surges can be highly destructive and the channelizing effect of levees can significantly alter an impact area. In our previous research we developed a depth-averaged theory for segregation that allowed segregation-mobility feedback effects to be incorporated easily into existing geophysical mass flows models. Numerical simulations showed that these captured the morphology of leveed fingers, as well as complex nonlinear coarsening, splitting and merging behaviour, but there was also an unexpected problem indicating that some important physics, related to dissipation, is missing in the model. We aim to identify the physical dissipation mechanisms involved. Small-scale analogue experiments and large-scale flume tests with our United States Geological Survey (USGS) partners will be used to study key flows that yield important insights into the nature of the dissipation, e.g. (i) the size of large particle recirculation cells (ii) the evolution of bouldery flow fronts (iii) the inception and coarsening dynamics of roll-waves and (iv) the velocity profile between levee walls. We will also go to the Pumice Plain of Mount St Helens, which is a virtually unique natural laboratory rich with information on the processes and conditions that led to both strongly leveed flows as well as spreading flows. These deposits have now been cross-cut by streams, which will allow detailed transects to be examined and sampled to establish the size and density of pumice clasts that were deposited by the various phases of June, July and August 1980 eruptions. Our multi-fronted approach of theory, computation, large- and small-scale experiments and field work is extremely powerful and will shed critical light on the controlling physical conditions and processes, and lead to major advances in our understanding of these complex nonlinear flows.

预测地球物理质量流的耗尽行为，从而预测其影响范围和峰值破坏力，制定有效战略以改善世界各地“处于危险之中”人口的安全，是至关重要的。地球物理物质流包括雪崩、泥石流、火山碎屑流和火山泥流等多种自然灾害。它们都是湿颗粒流或干颗粒流的例子，其中“大”颗粒向流速最大的表面分离，并优先向流锋输送。在这里，它们可能被冲过，因分离作用而上升，并再循环形成砾质流锋面。这些颗粒比内部更细的颗粒更容易抵抗运动，要么是因为颗粒更粗糙，要么是因为在碎屑和火山碎屑流中，它们消散了赋予流动性的内部孔隙压力。这些分离-迁移反馈效应可导致破坏性的高质量浓度浪涌锋面的发展，并可导致扩散流自发地发展成叶状流和平整的通道，这些通道可以很容易地将质量长距离转移（流出）。这种自组织对灾害评估和减轻风险具有重要意义，因为大的浪涌可能具有高度破坏性，而堤防的渠化作用可以显著改变受影响地区。在我们之前的研究中，我们开发了一种深度平均理论，该理论允许将分离-迁移性反馈效应轻松纳入现有的地球物理质量流模型中。数值模拟表明，这些捕获了水平手指的形态，以及复杂的非线性粗化，分裂和合并行为，但也有一个意想不到的问题表明，一些重要的物理，与耗散有关，在模型中缺失。我们的目标是确定所涉及的物理耗散机制。与我们的美国地质调查局（USGS）合作伙伴进行的小规模模拟实验和大规模水槽试验将用于研究对耗散性质产生重要见解的关键流动，例如(i)大颗粒再循环单元的大小（ii）砾质流锋面的演变（iii）翻滚波的开始和粗化动力学以及（iv）堤防之间的速度分布。我们还将前往圣海伦斯山的浮石平原，这是一个独特的自然实验室，拥有丰富的过程和条件信息，这些信息导致了强烈的平整流和扩散流。这些沉积物现在已被河流横切，这样就可以对详细的样带进行检查和取样，以确定1980年6月、7月和8月火山爆发的不同阶段沉积的浮石碎屑的大小和密度。我们的理论、计算、大型和小规模实验和实地工作的多方面方法非常强大，将在控制物理条件和过程方面发挥关键作用，并导致我们对这些复杂非线性流动的理解取得重大进展。