Clermont Université, Université Blaise Pascal, Laboratoire Magmas et Volcans, BP 10448, F-63000 Clermont-Ferrand, France.
Nature. 2012 Feb 1;482(7383):77-80. doi: 10.1038/nature10706.
Caldera-forming volcanic eruptions are low-frequency, high-impact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days, with devastating effects on local and global scales. Because no such eruption has been monitored during its long build-up phase, the precursor phenomena are not well understood. Geophysical signals obtained during recent episodes of unrest at calderas such as Yellowstone, USA, and Campi Flegrei, Italy, are difficult to interpret, and the conditions necessary for large eruptions are poorly constrained. Here we present a study of pre-eruptive magmatic processes and their timescales using chemically zoned crystals from the 'Minoan' caldera-forming eruption of Santorini volcano, Greece, which occurred in the late 1600s BC. The results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption. Despite the large volume of erupted magma (40-60 cubic kilometres), and the 18,000-year gestation period between the Minoan eruption and the previous major eruption, most crystals in the Minoan magma record processes that occurred less than about 100 years before the eruption. Recharge of the magma reservoir by large volumes of silicic magma (and some mafic magma) occurred during the century before eruption, and mixing between different silicic magma batches was still taking place during the final months. Final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period, with major growth phases immediately before eruption. These observations have implications for the monitoring of long-dormant, but potentially active, caldera systems.
破火山口型火山喷发是低频、高影响的事件，能够在数小时至数天的时间内以爆炸的方式释放数十到数千立方公里的岩浆，对局部和全球范围都具有毁灭性的影响。由于在其长期积聚阶段没有监测到这样的喷发，因此前兆现象还不太清楚。在美国黄石和意大利坎皮弗莱格雷等火山口近期的不稳定事件中获得的地球物理信号难以解释，而且对于大型喷发所需的条件也知之甚少。在这里，我们使用来自希腊圣托里尼火山“米诺斯”破火山口喷发的化学分带晶体研究了喷发前的岩浆过程及其时间尺度，该喷发发生在公元前 17 世纪后期。研究结果深入了解了大型硅质系统可能会多快从静止状态转变为喷发边缘状态。尽管喷发的岩浆量很大（40-60 立方公里），而且米诺斯喷发与上一次主要喷发之间的间隔时间为 18000 年，但米诺斯岩浆中的大多数晶体记录的都是在喷发前不到约 100 年发生的过程。在喷发前的一个世纪里，大量的硅质岩浆（和一些镁铁质岩浆）补给了岩浆储层，并且不同的硅质岩浆批次之间仍在混合。大型硅质岩浆储层的最终组装可能发生在地质上非常短的时间尺度上，与之前的休眠期相比，在喷发前的最后几个月会有主要的增长阶段。这些观测结果对监测长期休眠但可能活跃的破火山口系统具有重要意义。
