Shock wave hazards during explosive volcanic eruptions: an experimental investigation

火山爆发时的冲击波研究得很少。关于其产生和传播的几个问题仍有很大的争论，相关的危害目前在活火山地区的风险评估中被低估了。最近从1982年Chichón火山爆发所摧毁的一个村庄（墨西哥）找到了这种现象的证据。在一根钢杆的表面发现了火山灰颗粒撞击产生的微小陨石坑。通过分析方法计算，撞击的速度可达980米/秒，与理论和数值上报道的伴随火山爆发的冲击波的速度相似。这项提议的主要目标是更好地了解不同大小/质量的火山颗粒被激波加速的机制，要么是由于与气相的有效动量耦合，要么是由于与颗粒接触时激波结构的变化。我们计划在实验中再现金属靶上的撞击坑。需要回答的问题是：1)在激波存在的情况下，粒子加速的主要过程是什么？2)粒径、质量载荷、颗粒形状与计算出的高速之间的关系是什么？3)撞击时钢材的温度是决定“弹坑”大小的重要因素吗？这项研究的预期结果将：(1)阐明爆炸爆发期间冲击波传播的相关过程；(2)有助于提高对这些现象相关危害的认识，同时改进具体的应对策略。

Shock waves in explosive volcanic eruptions are poorly investigated. Several issues concerning their generation and propagation are still objects of great debate, and the associated hazards are currently downplayed in active volcanic area risk assessment. Evidence for such phenomena was recently recovered from one of the villages destroyed by the 1982 eruption of El Chichón volcano (Mexico). Micrometric craters produced by the impact of volcanic ash particles were found on the surface of a steel pole. The velocities of the impacts, was calculated by analytical methods as up to 980 m/s, similar to those reported theoretically and numerically for shock waves accompainying volcanic eruptions. The main goal of this proposal is to gain better insight into the mechanisms by which volcanic particles of different size/mass can be accelerated by shock waves, either given efficient momentum coupling with a gas phase or due to changes in the shock structure at the contact with particles. We plan to reproduce experimentally the impact craters on metal targets. Questions to be answered are: 1) What is the main process responsible for particle acceleration in the presence of shock waves? 2) What is the relationship between the grain-size, the mass load, the shape of the particles, and the high velocities calculated? 3) Is the steel’s temperature at the moment of impact an important factor in determining the magnitude of “cratering”? The results expected from this investigation, will 1) elucidate the processes associated with shock wave propagation during explosive eruptions, and 2) help to raise awareness about the hazards related to these phenomena while improving specific response strategies.