We present the results of analogue laboratory experiments on pyroclastic fountain collapse. Mixtures of air and glass beads ranging in size around 75 ± 15 μm, with Stokes number of ~10⁻³−10¹ and representative of 0.1–1 mm sized particles in nature, were released from a hopper at heights of 0.45–2.95 m above the base of a horizontal channel. Free fall caused continuous dilation of the granular material and led to mean particle concentrations of ~9–36 vol%, with concentration inversely proportional to drop height, before the particles impacted the channel base. Decoupling between the particles and the ambient air upon impact caused deflation of the mixture, which then propagated laterally as a dense granular flow overridden by a dilute suspension. Measurements at the impingement surface revealed that pore fluid pressure, generated through high air-particle relative velocity during deflation, counterbalanced up to ~50% of the weight of the emerging granular flow. The runout distance of the dense flow increased linearly with the fall height, similar to published results on unidirectional flows generated from collapse of packed granular columns. This suggests that the runout of flows resulting from release of granular material is controlled essentially by conversion of potential to kinetic energy and that the initial particle concentration is a second order parameter. We conclude that fountaining of pyroclastic material containing large amounts of particles with Stokes numbers of the order 10⁻³−10¹ can generate dense pyroclastic flows with some degree of pore fluid pressure.

我们介绍了火成岩喷泉塌陷的模拟实验室实验的结果。空气和玻璃珠的混合物，尺寸约为75±15μm，斯托克斯数为〜10 ^-3 -10 ¹料斗在水平通道底部上方0.45-2.95 m的高度从料斗中释放出来，并且代表了自然界中大小为0.1–1 mm的代表性颗粒。自由落体导致颗粒物质不断膨胀，导致平均颗粒浓度约为9–36 vol％，浓度与液滴高度成反比，然后颗粒才撞击通道底部。撞击时，颗粒与环境空气之间的解耦导致混合物放气，然后混合物以致密的颗粒状流向侧面传播，被稀疏的悬浮液所覆盖。在撞击表面的测量结果表明，在放气过程中，通过较高的空气颗粒相对速度产生的孔隙流体压力可抵消高达约50％的新兴颗粒流重量。稠密流的跳动距离随下落高度线性增加，类似于已发表的有关填充颗粒柱坍塌产生的单向流的结果。这表明由粒状材料的释放引起的流动的跳动基本上是通过势能到动能的转换来控制的，并且初始颗粒浓度是二阶参数。我们得出的结论是，含有大量颗粒的斯托克斯数为10的火成碎屑材料的润润剂 这表明由粒状材料的释放引起的流动的跳动基本上是通过势能到动能的转换来控制的，并且初始颗粒浓度是二阶参数。我们得出的结论是，包含大量颗粒的斯托克斯数为10的火成碎屑材料的润润剂 这表明由粒状材料的释放引起的流动的跳动基本上是通过势能到动能的转换来控制的，并且初始颗粒浓度是二阶参数。我们得出的结论是，包含大量颗粒的斯托克斯数为10的火成碎屑材料的润润剂^-3 -10 ¹可以在一定程度的孔隙流体压力下产生致密的火山碎屑流。