Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization
Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization
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DOI：
10.1038/s41561-019-0468-6
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发表时间：
2019-12-01
影响因子：
18.3
通讯作者：
Lee, Peter D.
中科院分区：
文献类型：
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作者：
Arzilli, Fabio;La Spina, Giuseppe;Lee, Peter D.
玄武岩喷发是地球和行星上最常见的火山活动形式。玄武岩岩浆的低粘度抑制了碎裂，这有利于喷流和熔岩喷发活动，但也会发生高度爆炸性的、危险的玄武岩喷发。促进玄武岩岩浆碎裂的过程仍不清楚，也存在争议。在这里，我们使用了一个数值管道模型来表明，在爆发期间岩浆的快速上升会产生巨大的过冷。现场实验表明，过冷驱动结晶非常迅速(在几分钟内)，这导致粘度的阶跃变化，从而触发岩浆破碎。实验产生的结构与玄武岩普林尼期喷发产物一致。我们应用了一个数值模型来研究广泛的参数空间内的玄武岩岩浆破碎，发现所有玄武岩火山都有可能产生高度爆炸性的喷发。临界要求是岩浆初始温度低于1,100℃，才能达到30%以上的同步喷发晶体含量，因此岩浆粘度约为10(5)PaS，我们的结果表明，这是快速上升的玄武岩岩浆破碎所需的最低粘度。这些温度、晶体含量和粘度要求揭示了典型的喷流玄武岩火山如何产生意想不到的高度爆炸性和危险的喷发。
Basaltic eruptions are the most common form of volcanism on Earth and planetary bodies. The low viscosity of basaltic magmas inhibits fragmentation, which favours effusive and lava-fountaining activity, yet highly explosive, hazardous basaltic eruptions occur. The processes that promote fragmentation of basaltic magma remain unclear and are subject to debate. Here we used a numerical conduit model to show that a rapid magma ascent during explosive eruptions produces a large undercooling. In situ experiments revealed that undercooling drives exceptionally rapid (in minutes) crystallization, which induces a step change in viscosity that triggers magma fragmentation. The experimentally produced textures are consistent with basaltic Plinian eruption products. We applied a numerical model to investigate basaltic magma fragmentation over a wide parameter space and found that all basaltic volcanoes have the potential to produce highly explosive eruptions. The critical requirements are initial magma temperatures lower than 1,100 degrees C to reach a syn-eruptive crystal content of over 30 vol%, and thus a magma viscosity around 10(5) Pa s, which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas. These temperature, crystal content and viscosity requirements reveal how typically effusive basaltic volcanoes can produce unexpected highly explosive and hazardous eruptions.