Jones Thomas J, Russell James K, Brown Richard J, Hollendonner Lea
Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool, L69 3GP, UK.
Department of Earth, Ocean & Atmospheric Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
Nat Commun. 2022 Feb 22;13(1):992. doi: 10.1038/s41467-022-28633-w.
Volcanism on Earth and on other planets and satellites is dominated by the eruption of low viscosity magmas. During explosive eruption, high melt temperatures and the inherent low viscosity of the fluidal pyroclasts allow for substantial post-fragmentation modification during transport obscuring the record of primary, magmatic fragmentation processes. Here, we show these syn-eruption modifications, in the form of melt stripping and agglutination, to be advantageous for providing fundamental insights into lava fountain and jet dynamics, including eruption velocities, grain size distributions and melt physical properties. We show how enigmatic, complex pyroclasts termed pelletal lapilli form by a two-stage process operating above the magmatic fragmentation surface. Melt stripping from pyroclast surfaces creates a spray of fine melt droplets whilst sustained transport in the fountain allows for agglutination and droplet scavenging, thereby coarsening the grain size distribution. We conclude with a set of universal regime diagrams, applicable for all fluidal fountain products, that link fundamental physical processes to eruption conditions and melt physical properties.
地球上以及其他行星和卫星上的火山活动主要由低粘度岩浆的喷发所主导。在爆发性喷发期间，高温熔体以及流体状火山碎屑固有的低粘度使得在运输过程中发生大量破碎后改性，从而模糊了原生岩浆破碎过程的记录。在此，我们展示了以熔体剥离和凝集形式出现的这些同喷发改性，对于深入了解熔岩喷泉和射流动力学（包括喷发速度、粒度分布和熔体物理性质）具有重要意义。我们展示了被称为豆粒状火山砾的神秘复杂火山碎屑是如何通过在岩浆破碎面上方发生的两阶段过程形成的。从火山碎屑表面剥离熔体形成了细小熔体滴的喷雾，而在喷泉中持续运输则允许凝集和液滴清除，从而使粒度分布变粗。我们最后给出了一组适用于所有流体喷泉产物的通用状态图，这些图将基本物理过程与喷发条件和熔体物理性质联系起来。
