Melt stripping and agglutination of pyroclasts during the explosive eruption of low viscosity magmas

• Published in: Nature communications Vol. 13; no. 1; pp. 992 - 11
• Main Authors: Jones, Thomas J., Russell, James K., Brown, Richard J., Hollendonner, Lea
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 22.02.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 147/135; 704/2151/598; 704/4111; 704/445/598; Agglutination; Droplets; Eruptions; Fragmentation; Gas jets; Grain size; Grain size distribution; Humanities and Social Sciences; Lava; Magma; multidisciplinary; Particle size; Physical properties; Scavenging; Science; Science (multidisciplinary); Size distribution; Viscosity; Volcanic activity; Volcanic eruptions
• DOI: 10.1038/s41467-022-28633-w
• ISSN: 2041-1723

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. The pyroclast properties and features can provide insights into the dynamics of explosive eruptions of low viscosity magma. Here, the authors show how lava droplets, or pyroclasts are subject to melt removal and melt addition during transport in a gas jet and present a method to reconstruct eruption conditions from the pyroclast textures.