Piton de la Fournaise, situated on La Réunion island (France), is one of the most active hot spot basaltic shield volcanoes worldwide, experiencing at least two eruptions per year since the establishment of the volcanological observatory in 1979. Eruptions are typically fissure-fed and form extensive lava flow fields. About 95 % of some ∼ 250 historical events (since the first confidently dated eruption in 1708) have occurred inside an uninhabited horseshoe-shaped caldera (hereafter referred to as the Enclos), which is open to the ocean on its eastern side. Rarely (12 times since the 18th century), fissures have opened outside of the Enclos, where housing units, population centers, and infrastructure are at risk. In such a situation, lava flow hazard maps are a useful way of visualizing lava flow inundation probabilities over large areas. Here, we present the up-to-date lava flow hazard map for Piton de la Fournaise based on (i) vent distribution, (ii) lava flow recurrence times, (iii) statistics of lava flow lengths, and (iv) simulations of lava flow paths using the DOWNFLOW stochastic numerical model. The map of the entire volcano highlights the spatial distribution probability of future lava flow invasion for the medium to long term (years to decades). It shows that the most probable location for future lava flow is within the Enclos (where there are areas with up to 12 % probability), a location visited by more than 100 000 visitors every year. Outside of the Enclos, probabilities reach 0.5 % along the active rift zones. Although lava flow hazard occurrence in inhabited areas is deemed to be very low (< 0.1 %), it may be underestimated as our study is only based on post-18th century records and neglects older events. We also provide a series of lava flow hazard maps inside the Enclos, computed on a multi-temporal (i.e., regularly updated) topography. Although hazard distribution remains broadly the same over time, some changes are noticed throughout the analyzed periods due to improved digital elevation model (DEM) resolution, the high frequency of eruptions that constantly modifies the topography, and the lava flow dimensional characteristics and paths. The lava flow hazard map for Piton de la Fournaise presented here is reliable and trustworthy for long-term hazard assessment and land use planning and management. Specific hazard maps for short-term hazard assessment (e.g., for responding to volcanic crises) or considering the cycles of activity at the volcano and different event scenarios (i.e., events fed by different combinations of temporally evolving superficial and deep sources) are required for further assessment of affected areas in the future – especially by atypical but potentially extremely hazardous large-volume eruptions. At such an active site, our method supports the need for regular updates of DEMs and associated lava flow hazard maps if we are to be effective in keeping up to date with mitigation of the associated risks.

中文翻译：

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Piton de la Fournaise 火山熔岩流危险图

Piton de la Fournaise 位于留尼汪岛（法国），是世界上最活跃的玄武岩盾状火山热点之一，自 1979 年火山观测站成立以来，每年至少发生两次喷发。并形成广阔的熔岩流场。约 95% 的一些 ～ 250 次历史事件（自 1708 年第一次确定日期的喷发以来）发生在一个无人居住的马蹄形火山口（以下称为 Enclos）内，该火山口东侧向海洋开放。很少（自 18 世纪以来有 12 次）裂缝在 Enclos 之外开放，那里的住房单元、人口中心和基础设施都处于危险之中。在这种情况下，熔岩流危险图是可视化大面积熔岩流淹没概率的有用方法。在这里，我们基于 (i) 喷口分布、(ii) 熔岩流重现时间、(iii) 熔岩流长度的统计数据和 (iv) 模拟熔岩流动路径使用 DOWNFLOW 随机数值模型。整个火山图突出了未来熔岩流入侵中长期（数年至数十年）的空间分布概率。它表明未来熔岩流最有可能的位置是在 Enclos 内（其中有高达 12% 的可能性的区域），每年有超过 100 000 名游客访问该位置。在 Enclos 之外，沿着活动裂谷区的概率达到 0.5%。尽管有人认为在有人居住的地区发生熔岩流危害非常低（5 % 沿活动裂谷带。尽管有人认为在有人居住的地区发生熔岩流危害非常低（5 % 沿活动裂谷带。尽管有人认为在有人居住的地区发生熔岩流危害非常低（< 0.1 %)，可能会被低估，因为我们的研究仅基于 18 世纪后的记录，而忽略了较旧的事件。我们还在 Enclos 内提供了一系列熔岩流危险地图，这些地图是在多时间（即定期更新）地形上计算的。尽管随着时间的推移，灾害分布大致保持不变，但由于数字高程模型 (DEM) 分辨率的提高、不断改变地形的高频率喷发以及熔岩流维度特征和路径，在整个分析期间都注意到了一些变化。此处展示的 Piton de la Fournaise 熔岩流危险图对于长期危险评估以及土地利用规划和管理而言是可靠且值得信赖的。用于短期危害评估的特定危害地图（例如，以应对火山危机）或考虑火山活动的周期和不同的事件情景（即，由时间演变的表层和深层源的不同组合引发的事件）需要在未来进一步评估受影响的地区——尤其是非典型的但潜在的极其危险的大面积喷发。在这样一个活跃的地点，我们的方法支持定期更新 DEM 和相关熔岩流危险图的需要，如果我们要有效地跟上缓解相关风险的最新情况。由不同时间演变的浅源和深源的不同组合提供的事件）需要在未来进一步评估受影响的地区——特别是非典型但潜在的极其危险的大容量喷发。在这样一个活跃的地点，我们的方法支持定期更新 DEM 和相关熔岩流危险图的需要，如果我们要有效地跟上缓解相关风险的最新情况。由不同时间演变的浅源和深源的不同组合提供的事件）需要在未来进一步评估受影响的地区——特别是非典型但潜在的极其危险的大容量喷发。在这样一个活跃的地点，我们的方法支持定期更新 DEM 和相关熔岩流危险图的需要，如果我们要有效地跟上缓解相关风险的最新情况。