Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, Reykjavik IS-101, Iceland.
Nature. 2010 Nov 18;468(7322):426-30. doi: 10.1038/nature09558.
Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During such eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajökull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic, closing airspace over much of Europe for days. This eruption was preceded by an effusive flank eruption of basalt from 20 March to 12 April 2010. The 2010 eruptions are the culmination of 18 years of intermittent volcanic unrest. Here we show that deformation associated with the eruptions was unusual because it did not relate to pressure changes within a single magma chamber. Deformation was rapid before the first eruption (>5 mm per day after 4 March), but negligible during it. Lack of distinct co-eruptive deflation indicates that the net volume of magma drained from shallow depth during this eruption was small; rather, magma flowed from considerable depth. Before the eruption, a ∼0.05 km(3) magmatic intrusion grew over a period of three months, in a temporally and spatially complex manner, as revealed by GPS (Global Positioning System) geodetic measurements and interferometric analysis of satellite radar images. The second eruption occurred within the ice-capped caldera of the volcano, with explosivity amplified by magma-ice interaction. Gradual contraction of a source, distinct from the pre-eruptive inflation sources, is evident from geodetic data. Eyjafjallajökull's behaviour can be attributed to its off-rift setting with a 'cold' subsurface structure and limited magma at shallow depth, as may be typical for moderately active volcanoes. Clear signs of volcanic unrest signals over years to weeks may indicate reawakening of such volcanoes, whereas immediate short-term eruption precursors may be subtle and difficult to detect.
岩浆房的逐渐膨胀通常先于高活跃度火山的喷发。在这种喷发中，当岩浆流出压力降低时，会迅速放气。对于活跃度适中的火山，如冰岛的埃亚菲亚德拉冰盖火山，人们对其变形方式了解较少。2010 年 4 月 14 日，这座火山开始爆发流纹英安岩，形成了一次剧烈的火山顶喷发，导致航空交通异常中断，欧洲大部分地区的空域关闭了数天。这次喷发之前，2010 年 3 月 20 日至 4 月 12 日，火山曾发生过玄武岩的喷发。2010 年的喷发是 18 年来间歇性火山活动的高潮。在这里，我们表明，与喷发相关的变形是不寻常的，因为它与单个岩浆房内的压力变化无关。在第一次喷发之前，变形速度很快（3 月 4 日之后每天超过 5 毫米），但在喷发期间可以忽略不计。没有明显的同期放气表明，在此期间，从浅层深度排出的岩浆净体积很小；相反，岩浆是从相当深的地方流出的。喷发前，一个约 0.05km3 的岩浆侵入体在三个月的时间里以时间和空间复杂的方式增长，这是通过全球定位系统（GPS）大地测量测量和卫星雷达图像的干涉分析揭示的。第二次喷发发生在火山的冰盖火山口内，由于岩浆-冰相互作用，爆炸威力得到增强。大地测量数据显示，与喷发前的膨胀源不同的源逐渐收缩。埃亚菲亚德拉冰盖火山的行为可以归因于其处于裂谷外的位置，具有“冷”的地下结构和浅层深度有限的岩浆，这可能是活跃度适中的火山的典型特征。多年至数周的火山活动异常的明显迹象可能表明这些火山重新活跃，而即时的短期喷发前兆可能很微妙且难以察觉。
