实验模拟侧向遮挡对低密度火山碎屑流的影响——对日本云仙岳火山1991年火山碎屑流的启示

本文将颗粒驱动重力流实验流体与自然界低密度火山碎屑流进行标度化研究，探讨低密度火山碎屑流的流动行为。通过在矩形流体交换水箱中放置占水箱宽度1/4、1/2、3/4比例的侧向遮挡障碍物，调查了颗粒驱动重力流实验流体在遇到侧向遮挡前后的运动模式、流体前锋速度减速特征和颗粒堆积分布特征。实验结果显示出不同比例的部分遮挡对低密度火山碎屑流影响的复杂性。实验表明，1/4比例的部分遮挡能够提高低密度火山碎屑流在通过之后的流速，并增加通过遮挡的颗粒堆积总量，能够解释日本云仙岳火山1991年6月3日喷发形成的碎屑流流动特征。在侧向遮挡比例为1/2时，~100T的时间内流体前锋减速，并在~100T之后加速（T为无量纲时间）；通过遮挡的堆积物总量明显减少。通过3/4比例的侧向遮挡之后，颗粒实验流体前锋持续减速，颗粒堆积总量减少。

Experimental study of partial vertical block effects on dilute pyroclastic density currents: Implications for Unzen pyroclastic flows in 1991, Japan

Dilute pyroclastic density currents behaviors were experimentally studied by the scaled particle-driven gravity currents. Lateral partial blocks which had ratios of 1/4, 1/2 and 3/4 of the tank width were set up in a lock-exchange tank. The kinematic characters, front acceleration/deceleration modes and deposition patterns of flows, both before and after blocks were investigated in this paper. Partial blocks showed complex effects on PDCs. Experiments showed that the 1/4 lateral partial block exerted an acceleration of flow front speed and an increasing of sedimentation on dilute pyroclastic density currents. This result could provide an explanation for behaviors of pyroclastic flows in Unzen volcano (Japan), which erupted on June 3, 1991. The 1/2 lateral partial blocks decelerated front speed within~100T (T is the dimensionless time), then accelerated after~100T, and decreased total particle sediments of the dilute experimental currents after lateral blocks. The 3/4 lateral partial blocks decelerated flow front speed and decreased the total particle sediments after them.