In situ granulation by thermal stress during subaqueous volcanic eruptions
In situ granulation by thermal stress during subaqueous volcanic eruptions
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DOI：
10.1130/g45503.1
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发表时间：
2019-02-01
期刊：
影响因子：
5.8
通讯作者：
Dingwell, Donald B.
中科院分区：
文献类型：
--
作者：
Colombier, Mathieu;Scheu, Bettina;Dingwell, Donald B.
一些最复杂的火山热力学过程发生在喷发的岩浆与水相互作用时。在浅水区，“苏尔采扬”喷发是壮观的，它们有效地将岩浆破碎成细小的火山灰颗粒。这些火山喷发对航空的危害取决于所产生的可运输细灰的数量，以及它是否聚集成颗粒涂层或堆积物。为了研究这两种机制，我们使用X射线计算机断层扫描和电子显微镜分析了Capelinhos（亚速尔群岛，1957-1958年）和Hunga Tonga-Hunga Ha'apai（汤加，2014-2015年）的Surtseyan火山爆发的火山灰。我们发现的火山碎屑没有涂层，严格意义上说，但有包裹灰产生的颗粒表面原位造粒。这是由热应力引起的，因为火山碎屑短暂地穿过水，并在喷发过程中被淬火。因此，在浅水下喷发中，原位造粒是一个重要的二次破裂过程。我们的研究结果表明，火山灰包裹并不总是颗粒聚集和吸积的证据，但它也可能是由于新的火山灰形成。浅水条件产生最有效的灰生成条件，导致顺风人口和空中交通的最大危险。
Some of the most complex volcanic thermodynamic processes occur when erupting magma interacts with water. In shallow water, "Surtseyan" eruptions are spectacular, and they efficiently fragment magma into fine ash particles. The aviation hazard from these eruptions depends the amount of transportable fine ash that is generated and whether it is aggregated into particle coatings or accretions. To investigate both mechanisms, we analyzed ash-encased lapilli from the Surtseyan eruptions of Capelinhos (Azores, 1957-1958) and Hunga Tonga-Hunga Ha'apai (Tonga, 2014-2015) using X-ray computed microtomography and electron microscopy. We discovered pyroclasts that were not coated, sensu stricto, but had enveloping ash produced by in situ granulation of the particle surface. This was caused by thermal stress as pyroclasts briefly traveled through water and were quenched during eruption. In situ granulation is thus an important secondary disruption process in shallow subaqueous eruptions. Our results imply that ash encasement is not always evidence of particle aggregation and accretion, but it may also result from new ash formation. Shallow-water conditions produce the most efficient ash-generation conditions, leading to the greatest hazard to downwind populations and air traffic.