Pyroclastic currents (PCs) are the most challenging volcanic hazards for disaster planners in populated areas around volcanoes. “El Misti” volcano (5,825 m above sea level), located only 17 km from the city center of Arequipa (>1.1 million inhabitants), South Peru, has produced small-to-moderate volume (<1 km³) PCs with a frequency of 2,000–4,000 years over the past 50 kyr. The most recent Plinian eruption dated at 2070 cal yr BP (VEI 4) has been selected as one of the reference events for the hazard assessment and risk mitigation plan of Arequipa. Associated pumice- and lithic-rich PC deposits were emplaced from at least four phases of column-collapse into the radial valleys draining the volcano as far as 13 km toward the city. Field mapping and stratigraphic surveys conducted in seven valleys affected by the 2070 cal yr BP PCs were combined with a new high-resolution (2 m) digital surface model of the volcano to better estimate the distribution of individual PC volumes. Such data acquisition is particularly critical for two of these valleys (San Lázaro and Huarangal-Mariano Melgar) for which the medial and distal reaches now cross the suburbs of Arequipa. The total area covered by the PC deposits is estimated at 141 km² for a total bulk volume estimated at 406 ± 140 × 10⁶ m³. These volumes were used as input parameters to better calibrate probabilistic numerical simulations of future similar PC events using the two-layer VolcFlow model and assess the impacts of both the concentrated and dilute portions of these currents in the San Lázaro and Huarangal valleys. We discuss probability values of PC inundation obtained from these simulations both in terms of their implications for the dynamics of such hazardous PCs at El Misti and for their integration into its current multi-hazard assessment. Modeling results demonstrate that the risk of overbank processes and spreading of unconfined PCs inside Arequipa should be refined. This multi-disciplinary study aims to help the civil authorities’ understanding of the likely effects of PCs associated with a similar VEI 4 eruption of El Misti on the urban area of Arequipa.

对于火山周围人口稠密地区的灾害规划者来说，火山碎屑流（PC）是最具挑战性的火山灾害。“厄尔尼诺米斯蒂”火山（海拔5,825 m），距秘鲁南部阿雷基帕（> 110万居民）市中心仅17公里，产生的体积小至中等（<1 km ^3））在过去50年中使用频率为2,000–4,000年的PC。日期为2070年BP（VEI 4）的最近一次普利尼亚火山喷发已被选为阿雷基帕（Arequipa）危害评估和风险缓解计划的参考事件之一。从至少四个阶段的柱塌陷开始，富集了浮石和石屑的PC沉积物进入了放射状的山谷，向火山排放了13公里。在受2070年BP PC影响的七个山谷中进行的野外测绘和地层调查与火山的新高分辨率（2 m）数字地面模型相结合，可以更好地估计单个PC体积的分布。这样的数据采集对于其中两个河谷（圣拉萨罗河和瓦朗加尔－马里亚诺·梅尔加河）尤其重要，这些河谷的中端和远端现在穿越了阿雷基帕的郊区。PC沉积物覆盖的总面积估计为141 km²，总体积估计为406±140×10 ⁶  m ³。这些量用作输入参数，以便使用两层VolcFlow模型更好地校准未来类似PC事件的概率数值模拟，并评估这些水流的集中和稀释部分对SanLázaro和Huarangal山谷的影响。我们讨论了从这些模拟中获得的PC淹没的概率值，既涉及它们对El Misti这类危险PC的动力学的影响，又包括它们融入当前的多危害评估中的意义。建模结果表明，应提高在Arequipa内过度处理和无限制PC扩散的风险。这项多学科研究旨在帮助民政部门了解与类似的El Misti VEI 4爆发对阿雷基帕市区相关的PC可能产生的影响。