岩漿結晶使火山爆發更加劇烈

原文網址：https://www.manchester.ac.uk/discover/news/magma-crystallisation-makes-volcanoes-more-explosive/

岩漿結晶使火山爆發更加劇烈

曼徹斯特大學的科學家發表的新論文，發現了為何有些火山爆發比其他的更加猛烈。

玄武岩噴發是最常見的火山噴發型式，它們的岩漿活動相對來說大都較為溫和。但偶爾它們的岩漿活動會產生相當猛烈的火山爆發並造成災害，這種類型的噴發型式稱為普林尼型噴發，名稱來自於描述西元79年維蘇威火山噴發的古羅馬作家小普林尼。

在發表於期刊《自然―地球科學》(Nature Geoscience)的新論文「極為劇烈的玄武岩噴發中由快速結晶引發的岩漿破碎作用」中，作者提出了導致這種差異的原因。當岩漿從火山內部快速噴出時溫度會跟著迅速下降，使得結晶產生，造成岩漿的黏滯性急劇升高。這會進一步讓岩漿破碎，導致十分猛烈的火山爆發。

曼徹斯特大學的Fabio Arzilli和他的同事在位於牛津郡的鑽石光源設施進行了原位(in situ)與非原位(ex situ)實驗，並且結合數值模擬的結果而發現這項作用。此外，他們也觀察了自然情況下由玄武岩的猛烈噴發產生的岩石樣品，像是紐西蘭1886年發生的塔拉威拉火山爆發。

Arzilli博士表示：「在符合極為猛烈的火山噴發勢必會發生的條件下，我們發現岩漿上升的過程中，短短幾分鐘之內就能發生結晶作用。」

之前關於岩漿結晶作用的研究結果，使火山學家認為此作用發生的速度太慢，因此不可能導致極為猛烈的火山爆發。

Arzilli博士如此評價論文得出的發現：「我們的結果暗示了地球上所有的玄武岩火山系統，都有可能產生相當強烈的噴發。」

他接著表示：「不只從區域上來看，甚至就全球而言這項結果對於火山災害及風險都有相當重要的意義。事實上在英國的《全國緊急事務風險清單》中，就把冰島火山爆發造成的風險列為最優先考量的項目之一。」

Magma crystallisation makes volcanoes more explosive

A new paper from scientists at The University of Manchester has discovered why some volcanic eruptions are more explosive than others.

Basaltic eruptions are the most common form of volcanic eruption, and for the most part, they involve relatively tame magma activity. Occasionally, however, the magma activity results in highly explosive and hazardous eruptions. The latter are known as Plinian eruptions, after the Ancient Roman writer who described the eruption of Mt Vesuvius in 79AD.

A new paper, "Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallisation", published in the journal Nature Geoscience, proposes an explanation for this discrepancy. When magma is rapidly expelled from a volcano, it undergoes rapid cooling. This induces the formation of crystals, resulting in a sudden increase in the viscosity of the magma. In turn, this produces magma fragmentation, creating a highly explosive eruption.

Dr Fabio Arzilli, from The University of Manchester, and his colleagues discovered this process using a combination of numerical modelling and in situ and ex situ experiments. They also observed natural samples from previous highly explosive basaltic eruptions, such as the 1886 Tarawera eruption in New Zealand. The work was carried out with partners at the Oxfordshire-based Diamond Light Source.

Dr Arzilli said; “We found that, under certain conditions consistent with highly explosive eruptions, crystallisation can occur within a couple of minutes during magma ascent.”

Previous research into magma crystallisation had led volcanologists to believe it occurred too slowly to be responsible for highly explosive eruptions.

Commenting on the findings of the paper, Dr Arzilli said; “Our results imply that all basaltic systems on Earth have the potential to produce powerful explosive eruptions.”

He continued; “This has important implications for the volcanic hazard and risk, on not only the regional, but also the global scale. Indeed, Icelandic eruptions are recognised as one of the highest priority risks in the National Risk Register of Civil Emergencies for the UK population.”

Fabio Arzilli, Giuseppe La Spina, Mike R. Burton, Margherita Polacci, Nolwenn Le Gall, Margaret E. Hartley, Danilo Di Genova, Biao Cai, Nghia T. Vo, Emily C. Bamber, Sara Nonni, Robert Atwood, Edward W. Llewellin, Richard A. Brooker, Heidy M. Mader, and Peter D. Lee. Magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization. Nature Geoscience, 2019 DOI: 10.1038/s41561-019-0468-6

引用自：University of Manchester. ”Magma crystallisation makes volcanoes more explosive.”