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（>1立方公里的裂缝喷发）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，在整个北方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，作为最高优先风险之一。2014年10月20日之后的某个时候，Holuhraun火山爆发达到了洪水玄武岩的规模。它是自1783-84年拉基火山爆发以来冰岛最大的洪水玄武岩，该火山爆发导致超过20%的冰岛人口因环境污染和饥荒而死亡，并可能通过含硫气体和气溶胶造成的空气污染增加欧洲的死亡率。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45 kt/天，这是在持续喷发期间很少观察到的释气速率，这表明每公斤喷发岩浆的硫含量（我们估计>0.35 wt%）超过了冰岛最近的其他喷发，也可能超过了全球其他历史上的玄武岩喷发，这引发了关于这些惊人数量的硫的起源的问题。缺乏有关的数据转换率的二氧化硫气体转化为气溶胶，气溶胶在羽流中的停留时间和这些气象因素的依赖性是限制我们的信心，在大气模型的能力，预测气体和气溶胶浓度在近场和远场从冰岛洪水玄武岩喷发。对喷发产物的初步研究突出了两个非凡的特征：（1）基质玻璃含硫量高达1000 ppm（对于脱气的熔体预期<100 ppm）并且是极其不均匀的，以及（2）基质玻璃中大量的硫化物液体小球在淬火时被“捕获”在分解的行为中，这表明硫不仅由熔体提供，而且还受到脱气过程中硫化物液体的分解的影响。这些观察结果突出了一个以前被忽视的，但可能非常大的硫储层，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了解这次喷发的极高硫产量，并对评估环境影响产生影响。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喷发的硫和亲铜金属预算。我们将跟踪硫化物液体的形成，通过脱气分解，SO2气体的脱气和转化为气溶胶。整个途径是不是很好地理解，特别是考虑到复杂性的快速岩浆上升率假设的Holuhraun岩浆和缺乏火山灰的羽流，这两个我们假设施加动力学约束硫加工系统的不同部分。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，以了解硫收支，并将其输入羽流化学和扩散模型，这对灾害监测至关重要。

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.