Debris flows often exhibit high mobility, leading to extensive hazards far from their sources. Although it is known that debris flow mobility increases with initial volume, the underlying mechanism remains uncertain. Here, we reconstruct the mobility–volume relation for debris flows using a recent depth‐averaged two‐phase flow model without evoking a reduced friction coefficient, challenging currently prevailing friction‐reduction hypotheses. Physical experimental debris flows driven by solid–liquid mass release and extended numerical cases at both laboratory and field scales are resolved by the model. For the first time, we probe into the energetics of the debris flows and find that, whilst the energy balance holds and fine and coarse grains play distinct roles in debris flow energetics, the grains as a whole release energy to the liquid due to inter‐phase and inter‐grain size interactions, and this grain‐energy release correlates closely with mobility. Despite uncertainty arising from the model closures, our results provide insight into the fundamental mechanisms operating in debris flows. We propose that debris flow mobility is governed by grain‐energy release, thereby facilitating a bridge between mobility and internal energy transfer. The initial volume of debris flow is inadequate for characterizing debris flow mobility, and a friction‐reduction mechanism is not a prerequisite for the high mobility of debris flows. By contrast, inter‐phase and inter‐grain size interactions play primary roles and should be incorporated explicitly in debris flow models. Our findings are qualitatively encouraging and physically meaningful, providing implications not only for assessing future debris flow hazards and informing mitigation and adaptation strategies, but also for unravelling a spectrum of earth surface processes including heavily sediment‐laden floods, subaqueous debris flows and turbidity currents in rivers, reservoirs, estuaries, and ocean. © 2020 John Wiley & Sons, Ltd.

中文翻译：

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由于固液质量释放，谷物能量释放决定了泥石流的流动性

泥石流经常表现出高流动性，导致远离其来源的广泛危害。尽管众所周知，泥石流的流动性会随着初始体积的增加而增加，但其潜在机制仍不确定。在这里，我们使用最新的深度平均两相流模型重建了泥石流的迁移率-体积关系，而没有引起减小的摩擦系数，这挑战了目前流行的减小摩擦的假设。该模型解决了由固-液质量释放驱动的物理实验泥石流以及实验室和现场规模的扩展数值案例。我们第一次探究了泥石流的能量学，并发现，尽管能量平衡保持不变，细颗粒和粗颗粒在泥石流能量学中扮演着独特的角色，由于相间和晶粒间尺寸的相互作用，整个谷物将能量释放到液体中，而这种谷物能量的释放与流动性密切相关。尽管模型关闭带来了不确定性，但我们的研究结果提供了对泥石流中运行的基本机制的深入了解。我们认为，泥石流的流动性受谷物能量释放的支配，从而促进了流动性与内部能量传递之间的桥梁。泥石流的初始体积不足以表征泥石流的流动性，而降低摩擦的机制并不是泥石流高流动性的先决条件。相比之下，相间和粒度间的相互作用起主要作用，应明确地纳入泥石流模型中。我们的发现从质上是令人鼓舞的，并且对身体有意义，这不仅对评估未来的泥石流危害，提供缓解和适应策略提供了启示，而且还揭示了一系列地表过程，包括大量沉积物洪水，水下泥石流和河流，水库，河口和海洋中的浊流。分级为4 +©2020 John Wiley＆Sons，Ltd.