Scharff Lea, Hort Matthias, Varley Nick R
CEN, Institut für Geophysik, Universität Hamburg, Hamburg, 20146, Germany.
CIIV, Facultad de Ciencias, Universidad de Colima, Colima, 28045, Mexico.
Sci Rep. 2019 May 14;9(1):7386. doi: 10.1038/s41598-019-43620-w.
Pyroclastic density currents are one of the most devastating volcanic hazards. Understanding their dynamics is a key to develop successful hazard mitigation strategies. The hazard associated with pyroclastic density currents is commonly investigated a posteriori from their deposits or a priori using analogue and numerical experiments. Despite the low probability of observing a natural moving pyroclastic density current, we present the first in-situ analysis of the internal particle velocities of pyroclastic density currents at Volcán de Colima using a Doppler radar. Our data show two Vulcanian explosions, immediately followed by column collapse and a first pyroclastic density current travelling down the south flank with an average speed of 30 m/s (>50 m/s maximum speed) to a distance of 3 km from the crater rim. The direction of the pyroclastic density current coincided with that of the radar beam enabling measurement of velocity spectra (histogram of particle velocities within the radar beam). The measurement geometry enables the simultaneous measurement of the dense undercurrent at the crater rim (with <20 m/s and an increasing echo power over 20 s) and the dilute cloud higher above the topography approaching the radar (with >20 m/s and approximately constant echo power). The presented data set may be used as a benchmark for future experimental and numerical models that simulate the dynamics of pyroclastic density currents. Using the measured velocities of the collapsing column as input for numerical models will permit the validation of the models for the prediction of the true run-out distance, and thus provide valuable information for hazard assessments.
火山碎屑密度流是最具破坏性的火山灾害之一。了解其动力学特性是制定成功的减灾策略的关键。与火山碎屑密度流相关的灾害通常是从其沉积物进行事后研究，或者通过模拟和数值实验进行事前研究。尽管观测到自然移动的火山碎屑密度流的概率很低，但我们首次使用多普勒雷达对科利马火山的火山碎屑密度流内部颗粒速度进行了现场分析。我们的数据显示了两次武尔卡诺式喷发，随后紧接着是火山柱崩塌，以及一股火山碎屑密度流以平均30米/秒（最大速度>50米/秒）的速度沿南翼向下流动，到达距离火山口边缘3公里处。火山碎屑密度流的方向与雷达波束的方向一致，从而能够测量速度谱（雷达波束内颗粒速度的直方图）。测量几何结构能够同时测量火山口边缘的浓密底流（速度<20米/秒，回波功率在20秒内增加）和地形上方较高处接近雷达的稀薄云（速度>20米/秒，回波功率大致恒定）。所呈现的数据集可作为未来模拟火山碎屑密度流动态的实验和数值模型的基准。将测量的崩塌柱速度作为数值模型的输入，将允许对模型进行验证，以预测真实的流动距离，从而为灾害评估提供有价值的信息。
