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Cracking the code: Empirical analysis of damage fracture occurrence, abundance and morphological complexity for natural and experimental volcanic ash particles.

Rachael J. M. Baxter 1, James D. L. White1, Tobi Dürig2, Arran Murch3, Rebecca J. Carey4, Andreas Auer5, Shane Cronin6, Judy Fierstein7

  • Affiliations:  1 Department of Geology, University of Otago, Dunedin, New Zealand; 2 Forensic Science Institute, Federal Criminal Police Office (BKA), Wiesbaden, Germany; 3 Tauranga City Council, Tauranga, New Zealand; 4 School of Natural Sciences, University of Tasmania, Hobart, Australia; 5 Department of Geoscience, Shimane University, Matsue, Japan; 6 School of Environment, The University of Auckland, Auckland, New Zealand; 7 Volcano Science Center, U.S. Geological Survey, Moffett Field, California, USA 

  • Presentation type: Talk

  • Presentation time: Monday 14:30 - 14:45, Room R290

  • Programme No: 3.3.6

  • Theme 3 > Session 3

Abstract

Fractography, the study of fractures in materials, components, and structures, is essential for understanding material failure mechanisms. Two key principles in fractography are: (1) greater energy exerted results in more fractures, and (2) higher energy release rates lead to increased fracture complexity. Using these principles, we conducted an empirical analysis of basaltic to rhyolitic ash particles from eruptions and analogue experiments to examine damage fracture types and abundances produced by different fragmentation processes. Fracture types and abundances were documented with high-resolution backscattered electron images of 4 phi (~63 um) ash fragments captured with a Zeiss FEG-SEM. Experimental particles representing thermal granulation, fuel-coolant-interaction (FCI) processes, abrasion, and shattered Prince Rupert Drops were compared with natural samples from eruptions including Surtsey, Havre, Katmai, Hunga, and Sakurajima. We introduce a Damage Fracture Intensity (DFI) index that accounts for fracture prevalence, relief, complexity, and interactions with glass-crystal boundaries. DFI values enable inference of relative energy densities and release rates associated with fragmentation processes recorded by the particles. Our results reveal narrower DFI variations in experimental samples compared to natural ones, reflecting the broader range of processes active in eruptions versus targeted mechanisms in experiments. Both natural and experimentally created samples, regardless of composition, when influenced by magma-water interactions showed a higher proportion of particles with extensive and complex damage fractures. These findings demonstrate the utility of DFI in linking particle damage to fragmentation energies and mechanisms, enhancing our understanding of eruptive and experimental fragmentation processes.