The source and longevity of sulphur in an Icelandic flood basalt eruption plume

在现代，我们第一次有机会直接研究洪水玄武岩对环境的影响（bb101km3的裂缝喷发）。洪水玄武岩喷发是冰岛最危险的火山情景之一，对整个北半球造成了巨大的社会和经济后果。2012年，洪水玄武岩喷发被列入英国国家风险登记册，成为最优先考虑的风险之一。2014年10月20日之后，Holuhraun火山喷发达到了洪水玄武岩的规模。它现在是冰岛自1783-84年拉基火山爆发以来最大的洪水玄武岩，那次火山爆发造成了环境污染和饥荒，导致冰岛人口的20%死亡，并可能因含硫气体和气溶胶造成的空气污染而增加欧洲的死亡率。在过去的几周里，来自Holuhraun的污染一直在加剧，10月26日（根据世界卫生组织的定义），冰岛的污染首次达到了“危险”水平。在9月18日至22日期间，二氧化硫通量达到45千吨/天，这是在持续喷发期间很少观察到的排气速度，这表明每公斤喷发岩浆的硫负荷（我们估计为0.35 wt%）超过了冰岛最近的其他喷发，也许也超过了全球其他历史上的玄武岩喷发，这就提出了关于这些惊人数量硫的来源的问题。由于缺乏SO2气体转化为气溶胶的速率、气溶胶在羽流中的停留时间以及这些数据对气象因子的依赖性，限制了我们对大气模式预测冰岛洪水玄武岩喷发近场和远场气体和气溶胶浓度的信心。对喷发产物的初步研究突出了两个不同寻常的特征：(1)基体玻璃含有高达1000ppm的硫（脱气熔体预计低于100ppm），并且非常不均匀；(2)基体玻璃中大量的硫化物液体球在淬火时被“捕获”分解，这表明硫不仅由熔体提供，而且由脱气过程中硫化物液体的分解提供。这些观测结果突出了一个以前被忽视但可能非常大的硫储集层，几乎没有留下岩石学记录。这些结果可能在某种程度上有助于理解这次喷发的极高硫产量，并对评估环境影响具有启示意义。该项目结合了一大群研究人员的专业知识，以更好地了解Holuhraun火山喷发的硫和亲铜金属预算。我们将跟随硫化物液体的形成，直到它们在脱气时的分解，到二氧化硫气体的脱气和转化为气溶胶。整个过程还没有被很好地理解，特别是考虑到Holuhraun岩浆的快速上升速率和羽流中缺乏灰烬的复杂性，我们假设这两者都对系统不同部分的硫加工施加了动力学约束。我们将对熔岩和地幔柱化学进行详细的岩石学、地球化学测量，以了解硫收支，并为地幔柱化学和分散模型提供数据，这对危害监测至关重要。

For the first time in the modern age we have the opportunity to study at first hand the environmental impact of a flood basalt (>1 km3 fissure eruption). Flood basalt eruptions are one of the most hazardous volcanic scenarios in Iceland and have had enormous societal and economic consequences across the northern hemisphere. A flood basalt eruption was included in the UK National Risk Register in 2012 as one of the highest priority risks. The Holuhraun eruption reached the flood basalt size sometime after 20 October 2014. It is now the largest flood basalt in Iceland since the Laki eruption in 1783-84, which caused the deaths of >20% of the Icelandic population by environmental pollution and famine and likely increased European levels of mortality through air pollution by sulfur-bearing gas and aerosol. The pollution from Holuhraun has been intensifying over the last few weeks, reaching a "Dangerous" level for the first time in Iceland on 26 October (as defined by the World Health Organisation). During 18-22 September, SO2 fluxes reached 45 kt/day, a rate of outgassing rarely observed during sustained eruptions, suggesting that the sulfur loading per kg of erupted magma (we estimate >0.35 wt%) exceeds both that of other recent eruptions in Iceland and perhaps also other historic basaltic eruptions globally, raising questions regarding the origin of these prodigious quantities of sulfur. A lack of data concerning conversion rates of SO2 gas into aerosol, the residence times of aerosol in the plume and the dependence of these on meteorological factors is limiting our confidence in the ability of atmospheric models to forecast gas and aerosol concentrations in the near- and far-field from Icelandic flood basalt eruptions. Preliminary study of the erupted products highlights two extraordinary features: (1) matrix glasses contain up to 1000 ppm sulfur (<100 ppm is expected for degassed melt) and are extremely heterogeneous and (2) abundant sulfide liquid globules in the matrix glass are "caught in the act" of breaking down on quenching, suggesting that sulfur is not only supplied by the melt, but also by the breakdown of sulfide liquid during degassing. These observations highlight a previously overlooked but potentially very large reservoir of sulfur that leaves little petrological record. These results might go some way towards understanding the extremely high sulfur yield of this eruption and have implications for assessing the environmental impact.This project combines the expertise of a large group of researchers to understand better the sulfur and chalcophile metal budget of the Holuhraun eruption. We will follow the formation of sulfide liquids, through to their breakdown on degassing, to the outgassing of SO2 gas and conversion to aerosol. The entire pathway is not well understood, particularly given complexities related to the rapid magma ascent rates postulated for the Holuhraun magmas and the lack of ash in the plume, both of which we hypothesise impose kinetic constraints on sulfur processing in different parts of the system. We will carry out detailed petrological, geochemical measurements of lavas and plume chemistry to understand the sulfur budget and to feed into models of plume chemistry and dispersion, which are essential for hazard monitoring.