Tephra particles in physically and chemically evolving volcanic plumes and clouds carry soluble sulphate and halide salts to the Earth’s surface, ultimately depositing volcanogenic compounds into terrestrial or aquatic environments. Upon leaching of tephra in water, these salts dissolve rapidly. Previous studies have investigated the spatial and temporal variability of tephra leachate compositions during an eruption in order to gain insight into the mechanisms of gas-tephra interaction which emplace those salts. However, the leachate datasets analysed are typically small and may poorly represent the natural variability and complexity of tephra deposits. Here, we have conducted a retrospective analysis of published leachate analyses from the 18 May 1980 eruption of Mount St. Helens, Washington, analysing the spatial structure of the concentrations and relative abundances of soluble Ca, Cl, Na and S across the deposits. We have identified two spatial features: (1) concentrated tephra leachate compositions in blast deposits to the north of the volcano and (2) low S/Cl and Na/Cl ratios around the Washington-Idaho border. By reference to the bulk chemistry and granulometry of the deposit and to current knowledge of gas-tephra interactions, we suggest that the proximal enrichments are the product of pre-eruptive gas uptake during cryptodome emplacement. We speculate that the low S/Cl and Na/Cl ratios reflect a combination of compositional dependences on high-temperature SO2 uptake and preferential HCl uptake by hydrometeor-tephra aggregates, manifested in terrestrial deposits by tephra sedimentation and fallout patterns. However, despite our interrogation of the most exhaustive tephra leachate dataset available, it has become clear in this effort that more detailed insights into gas-tephra interaction mechanisms are prevented by the prevalent poor temporal and spatial representativeness of the collated data and the limited characterisation of the tephra deposits. Future leachate studies should aim to extensively sample across tephra deposit limits whilst simultaneously characterising deposit stratigraphy and tephra chemistry, mineralogy and granulometry, taking steps to ensure the quality and comparability of collected leachate datasets.

中文翻译：

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圣海伦火山渗滤液成分的空间分析：对未来采样策略的影响

物理和化学演化的火山羽流和云中的火山灰颗粒将可溶性硫酸盐和卤化物盐带到地球表面，最终将火山形成的化合物沉积到陆地或水生环境中。将火山灰在水中浸出后，这些盐会迅速溶解。以前的研究调查了火山喷发期间火山灰渗滤液成分的空间和时间变化，以便深入了解气-火山灰相互作用的机制，这些相互作用使这些盐类发生。然而，分析的渗滤液数据集通常很小，可能无法很好地代表火山灰沉积物的自然变异性和复杂性。在这里，我们对 1980 年 5 月 18 日华盛顿圣海伦斯火山喷发的已发表渗滤液分析进行了回顾性分析，分析沉积物中可溶性 Ca、Cl、Na 和 S 的浓度和相对丰度的空间结构。我们已经确定了两个空间特征：(1) 火山北部爆炸沉积物中的火山灰渗滤液成分浓缩；(2) 华盛顿-爱达荷州边界附近的 S/Cl 和 Na/Cl 比率较低。通过参考沉积物的整体化学和粒度测定以及目前对瓦斯-火山灰相互作用的了解，我们建议近端富集是隐丘就位期间喷发前气体吸收的产物。我们推测，低 S/Cl 和 Na/Cl 比率反映了对高温 SO2 吸收的成分依赖性和水凝物-火山灰聚集体优先吸收 HCl 的组合，这在火山灰沉积和沉降模式的陆地沉积物中表现出来。然而，尽管我们对可用的最详尽的 tephra 渗滤液数据集进行了询问，但在这项工作中很明显，由于整理数据的普遍较差的时间和空间代表性以及 tephra 的有限特征，因此无法更详细地了解气体 - tephra 相互作用机制存款。未来的渗滤液研究应旨在在 tephra 矿床范围内广泛取样，同时表征沉积层地层和 tephra 化学、矿物学和粒度测定，采取措施确保收集的渗滤液数据集的质量和可比性。在这项工作中，很明显，由于所整理数据的普遍较差的时间和空间代表性以及火山灰沉积物的有限特征，无法更详细地了解瓦斯-火山灰相互作用机制。未来的渗滤液研究应旨在在 tephra 矿床范围内广泛取样，同时表征沉积层地层和 tephra 化学、矿物学和粒度测定，采取措施确保收集的渗滤液数据集的质量和可比性。在这项工作中已经清楚地表明，由于所整理数据的普遍较差的时间和空间代表性以及火山灰沉积物的有限特征，无法更详细地了解瓦斯-火山灰相互作用机制。未来的渗滤液研究应旨在在 tephra 矿床范围内广泛取样，同时表征沉积层地层和 tephra 化学、矿物学和粒度测定，采取措施确保收集的渗滤液数据集的质量和可比性。