Reconstructing magma storage and transport prior to giant Icelandic fissure eruptions

最近冰岛南部的Eyjafjallajokull火山喷发对英国产生了重大影响。2010年4月和5月，火山灰云严重扰乱了欧洲的航空业，导致全球经济生产力损失超过40亿美元。然而，与冰岛其他许多火山相比，这次喷发规模相对较小。公元1783年，拉基火山喷发在不到一年的时间里产生了大约15立方公里的熔岩和火山灰--大约是现在艾雅法拉火山事件的100倍。拉基火山喷发的影响是毁灭性的。火山灰落在英国，大量有毒烟雾被释放到大气中。火山气体的释放对冰岛人来说是灾难性的。氟化氢气体的危害尤其严重：人和牲畜患上了氟骨症，使骨骼变形。氟中毒和与之相关的饥荒导致冰岛21%的人口死亡。拉基火山喷发还释放出大量的火山气体中的硫，这些硫以致命的干雾扩散到欧洲和北美，这导致了随后3年的极端气候变化，包括1784年欧洲和北美的严寒冬季。这种极端天气加上火山气体对呼吸的影响，导致英国和法国的死亡率增加了25%。如果今天发生像拉基这样的喷发，对经济活动和人类健康的负面影响将是巨大的。除了上面讨论的危险之外，火山灰还会给航空带来危险。未来几个世纪，如果不是几十年，很可能会发生一次类似拉基火山的喷发。冰岛有记载的历史可以追溯到1200年前，在这段时间里发生了5次巨大的喷发，拉基是其中最年轻的一次。鉴于在可预见的未来有可能发生类似的毁灭性喷发，重要的是要利用对此类喷发前运行过程的了解来制定预测和风险管理战略。火山监测的基础是观察地震活动和地球表面的膨胀，以及随着岩浆在火山管道系统中移动而释放的气体。成功的预测依赖于在喷发前识别上升岩浆的指纹。自现代监测技术发展以来，从未发生过像拉基这样的喷发。因此，我们需要利用喷发期间释放的熔岩和火山灰的成分来重建岩浆在喷发前穿过地壳时的演化。我们将使用最先进的科学仪器来研究熔体包裹体的成分，熔体包裹体是指当晶体生长在地壳的岩浆室中时被困住的微小熔体。我们将使用包裹体及其宿主晶体的成分来确定岩浆在地壳中储存时形成气体的速率。这些观测将使我们能够追踪岩浆在喷发开始之前的储存和上升的历史。这些喷发前岩浆运动的模型将被用来预测在大规模玄武岩喷发之前上升的岩浆的指纹，这一指纹可能被火山监测策略识别。这项对拉基事件产物的法医研究将提高我们预测灾难性玄武岩喷发的能力。我们的研究对理解过去的大喷发也有意义，在过去的大喷发中，在很短的地质时间间隔内就产生了数百万立方公里的熔岩。这类事件与极端环境变化、全球迅速变暖和物种大规模灭绝有关。我们的方法将允许改进对这些巨大喷发释放的具有环境意义的火山气体的测量。

The recent eruption of the Eyjafjallajokull volcano in southern Iceland has had a significant impact on the UK. The ash cloud severely disrupted European aviation in April and May of 2010 leading to a loss of over $4 billion to global economic productivity. This eruption is, however, relatively small compared to that of many other Icelandic volcanoes. In 1783 AD, the eruption of the Laki volcano produced about 15 cubic kilometres of lava and ash in less than a year - about 100 times larger than the present Eyjafjallajokull event. The effects of the Laki eruption were devastating. Ash fell in the UK, and huge quantities of noxious fumes were released to the atmosphere. This volcanic gas release was catastrophic for the Icelandic population. Hydrogen fluoride gas was particularly damaging: people and livestock developed fluorosis, which deforms the bones. The combination of fluorosis and the associated famine contributed to the death of 21% of the Icelandic population. The Laki eruption also released large quantities of sulphur in volcanic gases, and this sulphur spread in a deadly dry fog over Europe and North America, which led to extreme climatic variability over the following 3 years, including a severely cold winter in Europe and North America in 1784. This extreme weather combined with the respiratory impact of the volcanic gases to cause a 25% increase in death rate in Britain and France. If an eruption like Laki were to take place today, the negative impacts on economic activity and human health would be significant. In addition to the dangers discussed above, volcanic ash would present dangers to aviation. It is likely that an eruption similar to Laki will take place in the next few centuries, if not decades. Recorded history in Iceland stretches back 1200 years, and in this time 5 giant eruptions have occurred, with Laki being the youngest of these eruptions. Given the possibility of a similar devastating eruption in the foreseeable future, it is important that understanding of the processes operating before such eruptions is used to develop forecasting and risk management strategies. Volcanic monitoring is based on observation of earthquake activity and swelling of the earth surface and gas release as magma shifts in the plumbing system of the volcano. Successful forecasting is dependent on identifying the fingerprint of rising magma prior to the eruption. Eruptions like Laki have not taken place since the development of modern monitoring techniques. Therefore we need to use the composition of the lava and ash released during the eruption to reconstruct the evolution of the magma as it rose through the crust before eruption. We will examine the compositions of melt inclusions, microscopic pockets of melt that are trapped as crystals grow in magma chambers in the crust, using state-of-the-art scientific instruments. We will use the composition of the inclusions and their host crystals to determine the rate at which gas forms from magma as it is stored in the crust. These observations will allow us to track the history of magma storage and ascent before the eruption starts. These models of pre-eruptive magma movement will be used to predict the fingerprint of magma rising before large basaltic eruptions, a fingerprint that might be recognised by volcano monitoring strategies. This forensic study of the products of the Laki event will lead to improvement in our ability to forecast the onset of catastrophic basaltic eruptions. Our study also has implications for the understanding of giant eruptions in the past, where millions of cubic kilometres of lava have been produced in short intervals of geological time. Such events have been linked to extreme environmental change, rapid global warming and mass extinction of species. Our approach will allow for improved measurement of the release of environmentally significant volcanic gases from these giant eruptions.