DataSheet1_A GIS-based multi-hazard assessment at the San Pedro volcano, Central Andes, northern Chile.PDF

Recent advances in the modeling of volcanic phenomena have allowed scientists to better understand the stochastic behavior of volcanic systems. Eruptions can produce various types of volcanic phenomena of different sizes. The size of a given volcanic phenomenon dominates its spatial distribution and is commonly represented by volume/mass parameters in the models that reproduce their behavior. Multi-hazard assessments depend on first-order parameters to forecast hazards at a given geographic location. However, few multi-hazard assessments consider the size of the eruption (e.g., tephra fallout) to co-parameterize the size of the accompanying phenomena (e.g., mass flows) in a given eruptive scenario. Furthermore, few studies simulate multi-phenomenon eruptive scenarios with semi-continuous variations in their size, something that allows a better quantification of the aleatoric variability of the system. Here, we present a multi-hazard assessment of the San Pedro volcano, a high-threat volcano from northern Chile, that produced two large-size Plinian eruptions (VEI 5 and 6) in the last 16 ka, and ten Strombolian eruptions (VEI 2) between 1870 and 2021 CE, with the latest occurring on 2 December 1960 CE. We use intra-scenarios (i.e., subdivisions of eruptive scenarios) to explore the size variability of explosive volcanic phenomena. The size of intra-scenarios is extrapolated from the largest-size deposits of each type of phenomenon from the geologic record of the San Pedro volcano. We simulate explosive intra-scenarios for tephra fallout, concentrated PDCs, and lahars, and effusive scenarios for blocky lava flows. On the local scale, mass flows are likely (66–100%) to affect transport and energy infrastructure within a 14 km radius of the volcano. On the regional scale, large-size eruptions (VEI 5) in the rainy season are about as likely as not (33–66%) to accumulate 1 cm of tephra on energy, transport, and mining infrastructure over a 50 km radius, and these same eruptions are unlikely (10–33%) to accumulate 1 cm of tephra on the city of Calama. This work shows how multi-phenomenon intra-scenarios can be applied to better quantify the aleatoric variability of the type and size of volcanic phenomena in hazard assessments.

近年来火山现象模拟研究的进展，使科学家得以更精准地解析火山系统的随机行为。火山喷发可产生多种规模各异的火山现象。特定火山现象的规模主导其空间分布格局，在复现其演化过程的模型中，通常以体积、质量参数作为表征指标。多灾害评估需以一级参数为基础，对特定地理区域的灾害风险开展预测。然而，鲜有多灾害评估会在给定喷发场景中，将喷发（如火山碎屑沉降（tephra fallout））的规模作为协同参数，用以量化伴随现象（如块体流）的规模。此外，极少有研究模拟规模呈半连续变化的多现象喷发场景——这类场景可实现对火山系统随机变异性的更精准量化。
本研究针对智利北部高威胁火山圣佩德罗火山（San Pedro volcano）开展多灾害评估。该火山在过去16 ka间曾发生两次大规模普林尼式喷发（Plinian eruption），火山爆发指数（Volcanic Explosivity Index，VEI）分别为5和6；并在公元1870年至2021年间发生10次斯特龙博利式喷发（Strombolian eruption，VEI 2），最后一次喷发发生于公元1960年12月2日。我们采用场景内细分（intra-scenario，即喷发场景的子划分）方法，探究爆发型火山现象的规模变异性。场景内细分的规模基于圣佩德罗火山地质记录中各类型现象的最大规模沉积体外推得到。我们模拟了火山碎屑沉降、集中式火山碎屑密度流（PDCs）以及火山泥流（lahars）的爆发型场景内细分，同时模拟了块状熔岩流的溢流式喷发场景。
在局地尺度上，块体流极有可能（概率66%~100%）影响火山周边14 km半径范围内的交通与能源基础设施。在区域尺度上，雨季发生的大规模喷发（VEI 5）有近乎均等的概率（33%~66%）在50 km半径范围内的能源、交通与矿业基础设施上堆积1 cm厚的火山碎屑；而这类喷发在卡拉马市（Calama）堆积1 cm厚火山碎屑的概率则较低（10%~33%）。
本研究展示了多现象场景内细分方法可如何应用于灾害评估中，以更精准地量化火山现象类型与规模的随机变异性。