Montanaro Cristian, Mortensen Anette Kærgaard, Weisenberger Tobias B, Dingwell Donald B, Scheu Bettina
Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Theresienstrasse 41, 80333 Munich, Germany.
Háaleitisbraut 68, 110 Reykjavík, Iceland.
Bull Volcanol. 2021;83(11):81. doi: 10.1007/s00445-021-01502-y. Epub 2021 Nov 2.
Krafla central volcano in Iceland has experienced numerous basaltic fissure eruptions through its history, the most recent examples being the Mývatn (1724‒1729) and Krafla Fires (1975-1984). The Mývatn Fires opened with a steam-driven eruption that produced the Víti crater. A magmatic intrusion has been inferred as the trigger perturbing the geothermal field hosting Víti, but the cause(s) of the explosive response remain uncertain. Here, we present a detailed stratigraphic reconstruction of the breccia erupted from Víti crater, characterize the lithologies involved in the explosions, reconstruct the pre-eruptive setting, fingerprint the eruption trigger and source depth, and reveal the eruption mechanisms. Our results suggest that the Víti eruption can be classified as a magmatic-hydrothermal type and that it was a complex event with three eruption phases. The injection of rhyolite below a pre-existing convecting hydrothermal system likely triggered the Víti eruption. Heating and pressurization of shallow geothermal fluid initiated disruption of a scoria cone "cap" via an initial series of small explosions involving a pre-existing altered weak zone, with ejection of fragments from at least 60-m depth. This event was superseded by larger, broader, and dominantly shallow explosions (~ 200 m depth) driven by decompression of hydrothermal fluids within highly porous, poorly compacted tuffaceous hyaloclastite. This second phase was triggered when pressurized fluids broke through the scoria cone complex "cap". At the same time, deep-rooted explosions (~ 1-km depth) began to feed the eruption with large inputs of fragmented rhyolitic juvenile and host rock from a deeper zone. Shallow explosions enlarging the crater dominated the final phase. Our results indicate that at Krafla, as in similar geological contexts, shallow and thin hyaloclastite sequences hosting hot geothermal fluids and capped by low-permeability lithologies (e.g. altered scoria cone complex and/or massive, thick lava flow sequence) are susceptible to explosive failure in the case of shallow magmatic intrusion(s).
The online version contains supplementary material available at 10.1007/s00445-021-01502-y.
冰岛的克拉夫拉中央火山在其历史上经历了多次玄武岩裂隙喷发，最近的例子是米湖（1724 - 1729年）和克拉夫拉火山大火（1975 - 1984年）。米湖火山大火以一次蒸汽驱动的喷发开始，形成了维提火山口。据推断，一次岩浆侵入是扰动维提火山口所在热液场的触发因素，但爆炸反应的原因仍不确定。在这里，我们对从维提火山口喷发的角砾岩进行了详细的地层重建，描述了爆炸中涉及的岩性，重建了喷发前的环境，确定了喷发触发因素和源深度，并揭示了喷发机制。我们的结果表明，维提火山喷发可归类为岩浆 - 热液型，并且是一个具有三个喷发阶段的复杂事件。在一个先前存在的对流热液系统下方注入流纹岩可能触发了维提火山喷发。浅层地热流体的加热和增压通过一系列最初涉及先前存在的蚀变弱区的小爆炸引发了一个火山渣锥“帽”的破坏，碎片从至少60米深处喷出。这一事件被由高度多孔、压实不良的凝灰质玻璃质碎屑岩内热液流体减压驱动的更大、更广泛且主要为浅层的爆炸（约200米深度）所取代。当加压流体突破火山渣锥复合体“帽”时，引发了第二阶段。与此同时，深部爆炸（约1千米深度）开始从更深区域为喷发提供大量破碎的流纹质幼岩和围岩。扩大火山口的浅层爆炸主导了最后阶段。我们的结果表明，在克拉夫拉，与类似地质环境一样，容纳热液流体且被低渗透性岩性（如蚀变火山渣锥复合体和/或块状、厚熔岩流序列）覆盖的浅层且薄的玻璃质碎屑岩序列在浅层岩浆侵入的情况下容易发生爆炸破坏。
在线版本包含可在10.1007/s00445 - 021 - 01502 - y获取的补充材料。
