Debris flows and lahars are dense masses of water and sediment which are common phenomena in mountainous and volcanic regions, respectively. Where these flows debouch into water bodies they can trigger impulse waves (tsunamis) and form subaqueous deposits. Such deposits are important indicators for areas at risk from debris flows, lahars, and tsunamis and form archives of past environmental conditions. Correctly interpreting this archive, however, depends on our understanding of the sedimentology and architecture of the deposits. While subaerial debris-flow deposits have been extensively studied, there is a comparative lack of understanding of the deposits of subaerial debris flows that debouch into a water body. We experimentally investigate the similarities and contrasts between subaerial and subaqueous debris-flow deposits for flows of various magnitudes and compositions initiated in a subaerial environment. We show that flows depositing on a subaqueous plane generally have a deposit area similar to flows forming in a subaerial setting. Deposits forming on a subaqueous plane, however, are typically shorter and wider with similar thickness, as a result of interactions between the flow and the reservoir water body. Both in subaerial and subaqueous environments the deposits form coarse-grained lateral levees and frontal snout margins. However, where the levees are able to laterally confine the subaerial flows leading to deposits with constant to tapering width, the subaqueous deposits widen with distance offshore because of flow fluidization. Moreover, the frontal snout is often very dispersed, a sharp frontal margin is absent, and many isolated particles are deposited in front of the main deposit margin as a result of interactions between the debris flow and the reservoir water body. These results largely agree with observations of subaqueous pyroclastic-flow deposits. The similarity in area of subaerial and subaqueous deposits suggests that we can apply empirical relations based on subaerial flows to estimate the inundation area and flow volume of subaerial–subaqueous flows.

中文翻译：

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地下触发的泥石流的地下和水下沉积物之间的异同：模拟实验研究

泥石流和泻湖是大量的水和沉积物，分别是山区和火山地区的普遍现象。在这些水流进入水体的过程中，它们会触发脉冲波（海啸）并形成水下沉积物。此类沉积物是受泥石流，海啸和海啸威胁的地区的重要指标，并形成过去环境状况的档案。然而，正确地解释该档案，取决于我们对沉积物的沉积学和构造的理解。虽然对地下泥石流沉积物进行了广泛的研究，但相对缺乏对进入水体中的地下泥石流沉积物的了解。我们通过实验研究了地下和水下水下泥石流沉积物在地下环境中引发的各种规模和组成的水流之间的相似性和差异。我们表明，沉积在水下平面上的流通常具有类似于在地下环境中形成的流的沉积面积。然而，由于水流与储层水体之间的相互作用，在水下平面上形成的沉积物通常较短且较宽，且厚度相似。在地下和水下环境中，沉积物都会形成粗颗粒的横向堤坝和额鼻部边缘。然而，在堤坝能够横向限制地下气流而导致沉积物具有恒定至逐渐变细的宽度的情况下，水下流沉积物由于流动流化而随着距离增加而变宽。此外，由于泥石流和储层水体之间的相互作用，额头通常非常分散，没有锋利的额叶边缘，许多孤立的颗粒沉积在主要沉积物边缘的前面。这些结果在很大程度上与水下火山碎屑流沉积物的观察结果一致。地下和水下水域面积的相似性表明，我们可以基于地下水流应用经验关系来估计地下水-南水流的淹没面积和流量。