PyroCLAST: a new experimental framework to investigate overspilling of channelized, concentrated pyroclastic currents

Abstract

Overspilling of channelized pyroclastic currents is a significant threat for population around volcanoes and remains poorly known• First experimental device built to investigate the overspilling of pyroclastic currents• We observe two types of overspills at the passage of a bend in the experimental channel

Physical properties of pyroclastic density currents: relevance, challenges and future directions

“…However, laboratory apparatus size limitations (e.g., channel width) constrain the particle length scales that can be used. In the most simplified cases, analogue materials such as glass beads have been employed due to their ease of use and resistance to abrasion (Roche et al, 2013;Smith et al, 2020;Gueugneau et al, 2022;Penlou et al, 2023). When using natural samples at benchtop scales, the grain size distribution is subsampled to include only fine particles to prevent wall effects and maintain relevant scaling [e.g., pore pressure diffusion timescale, as demonstrated by Girolami et al (2008)].…”

“…Similar to other complex granular media, the rheology of volcanic granular flows depends on various properties of the mixture, such as particle shape, density, and grain size distribution. In the past decade, advances in our understanding of PDC dynamics was aided by the development of experiments (Lube et al, 2015;Sulpizio et al, 2016;Smith et al, 2020;Gueugneau et al, 2022;Poppe et al, 2022) and use of tools from soft-matter physics, including the discrete-element method (Cundall and Strack, 1979), which can help us derive constitutive equations to describe granular flow rheology (e.g., μ(I)-rheology; Jop et al, 2006) and its interactions with the substrate (Breard et al, 2020;Breard et al, 2022). Although a bulk rheology that captures some of the complexity at micro-and mesoscales may be sufficient for depth-averaged models, 3D models require inputs such as particle-particle friction, particle-substrate friction, and particle-restitution coefficients (Breard et al, 2019a;Neglia et al, 2022), which are more challenging to measure than simple angle of repose or the H/L ratio.…”

Spontaneous Unsteadiness and Sorting in Pyroclastic Density Currents and their Deposits

“…Much of our understanding of PDCs comes from experimental modelling, which has used a wide variety of approaches and materials in order to explore different features and behaviors. The dense granular dominated regime has been explored using both short inertial (often dam-break) experiments, and more sustained long-lived supplies (Walker, 1981;Roche et al, 2004;Rowley et al, 2011;Smith et al, 2018;Gueugneau, Charbonnier and Roche, 2022). Dried, disaggregated natural PDC materials have been used in several experiments to observe the behaviors of pyroclastic charges (Girolami et al, 2010;Breard and Lube, 2017), although this leads to challenges in scaling, as particle sizes in the order of millimeters can be difficult to transport in laboratory scale flows, and the grainsize ranges in the laboratory are commonly narrower than those seen in natural deposits.…”

“…The simultaneous existence of both a dense underflow, and a turbulent over-riding cloud has been well established in nature (Bursik and Woods, 1996;Branney and Kokelaar, 2002;Ort et al, 2003;Valentine et al, 2019), and described by the differing particle transfer mechanisms between layers (Doyle et al, 2010;Doronzo, 2012). Simultaneous dense and dilute flow behavior has only occasionally been captured experimentally (Dellino et al, 2007;Breard and Lube, 2017); laboratory work to date has typically focused on understanding the behaviors of only one part of this two-layer system (Dellino et al, 2010;Girolami et al, 2010;Andrews and Manga, 2012;Chedeville and Roche, 2014;Smith et al, 2018;Gueugneau, Charbonnier and Roche, 2022).…”