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

至关重要的是，要预测地球物理物质流的耗尽行为，从而预测其影响区域和最大破坏力，制定有效战略，改善全世界“处于危险中”人口的安全。地球物理物质流包括各种自然灾害，包括雪崩、泥石流、火山碎屑流和火山泥流。它们都是湿颗粒流或干颗粒流的例子，其中“大”颗粒向表面分离，在表面处速度最大，并优先向流动前沿输送。在这里，它们可能溢出，因分离而上升，并再循环以产生巨砾流锋。这些倾向于比更细粒度的内部更能抵抗运动，因为颗粒更粗糙，或者因为在碎屑流和火山碎屑流中，它们消散了赋予流动性的内部孔隙压力。这些分离流动性反馈效应可导致破坏性高质量浓度浪涌前沿的发展，并可导致扩散流自发地发展出容易长距离转移质量的叶瓣和堤坝通道（跳动）。这种自我组织对灾害评估和风险缓解具有重要意义，因为大的浪涌可能具有高度破坏性，堤坝的渠化效应可能大大改变影响区域。在我们以前的研究中，我们开发了一个深度平均理论的隔离，允许隔离流动性反馈效应，可以很容易地纳入现有的地球物理质量流模型。数值模拟表明，这些捕获的形态堤坝手指，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，有关耗散，是失踪的模型。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关键流，这些流对耗散的性质产生重要的见解，例如（i）大颗粒再循环单元的大小（ii）巨石流前沿的演变（iii）滚波的起始和粗化动力学以及（iv）堤坝壁之间的速度分布。我们还将前往圣海伦山的浮石平原，这是一个几乎独一无二的天然实验室，它富含有关导致强烈堤流和扩散流的过程和条件的信息。这些沉积物现已被溪流横切，因此可以对详细的断面进行检查和取样，以确定1980年6月、7月和8月火山爆发各阶段沉积的浮石碎屑的大小和密度。我们的理论，计算，大规模和小规模实验和实地工作的多前沿方法是非常强大的，将揭示关键的控制物理条件和过程，并导致我们对这些复杂的非线性流动的理解的重大进展。

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.