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

在现代，我们第一次有机会第一手研究洪水玄武岩(&gt；1千米裂缝喷发)对环境的影响。洪水玄武岩喷发是冰岛最危险的火山情景之一，在整个北半球产生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，列为最高优先风险之一。2014年10月20日之后，和鲁伦火山喷发达到了洪水玄武岩的大小。它现在是自1783-84年拉基火山喷发以来冰岛最大的洪水玄武岩。拉基火山喷发导致冰岛20%的人口死于环境污染和饥荒，并可能增加欧洲因含硫气体和气溶胶造成的空气污染而死亡的水平。在过去的几周里，来自Holuhraun的污染一直在加剧，10月26日，冰岛首次达到“危险”水平(根据世界卫生组织的定义)。在9月18日至22日期间，SO2通量达到每天45kt，这是持续喷发期间很少观察到的放气速度，这表明每公斤喷发岩浆的硫负载量(我们估计为0.35wt%)既超过了冰岛最近的其他喷发，也超过了全球其他历史性的玄武岩喷发，引发了人们对这些惊人数量的硫的来源的疑问。缺乏关于二氧化硫气体向气溶胶的转化率、气溶胶在烟柱中的停留时间以及这些数据与气象因素的相关性的数据，限制了我们对大气模型预测冰岛洪水玄武岩喷发的近场和远场气体和气溶胶浓度的能力的信心。对喷发产物的初步研究突出了两个不同寻常的特征：(1)基质玻璃含有高达1000ppm的硫(脱气熔体预计为100ppm)，并且非常不均匀；(2)基质玻璃中丰富的硫化物液滴在淬火时“被捕获”分解，这表明硫不仅由熔体提供，而且通过脱气过程中硫化物液体的分解而提供。这些观察结果突显了一个以前被忽视但可能非常大的硫磺储藏库，几乎没有留下岩石学记录。这些结果可能在一定程度上有助于理解这次喷发产生的极高的硫磺产量，并对评估环境影响有影响。该项目结合了一大批研究人员的专业知识，以更好地了解和鲁伦火山喷发的硫和亲硫金属预算。我们将跟踪硫化物液体的形成，直到它们在脱气时的分解，再到SO2气体的出气和气溶胶的转化。整个过程还不是很清楚，特别是考虑到与Holuhraun岩浆假设的快速岩浆上升速率和羽流中缺乏火山灰相关的复杂性，我们假设这两个因素对系统不同部分的硫磺加工施加了动力学限制。我们将对熔岩和羽流化学进行详细的岩石学、地球化学测量，以了解硫的收支情况，并将其纳入对灾害监测至关重要的羽流化学和扩散模型。

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.