The influence of heterogeneity on the strength of volcanic rocks and the stability of lava domes

Abstract

The collapse of lava domes, inherently heterogeneous structures, represents a significant volcanic hazard.Numerical and analogue models designed to model dome instability and collapse have incorporated heterogeneity 2 in the form of discrete zones with homogeneous properties. Based on an assessment of dome rock heterogeneity, we explore whether material property heterogeneity ("diffuse" heterogeneity) within these discrete zones can promote dome instability. X-ray computed tomography shows that dome samples are characterised by high microstructural heterogeneities; e.g., porosity varies from 0.07 to 0.20 over millimetric lengthscales. To explore how microstructural heterogeneity influences sample-scale strength, we performed numerical simulations using Rock Failure and Process Analysis. The mean mechanical properties of the numerical samples were constant, and we introduced heterogeneity by varying their distribution using a Weibull probability function. The models show that increasing heterogeneity can reduce sample-scale strength by more than a factor of two. To explore the influence of dome-scale heterogeneity, we numerically generated lava domes in Particle Flow Code. The domes have the same bulk strength but are characterised by different degrees of heterogeneity by varying the distribution of cohesion using a Weibull probability function. The models show that a greater degree of heterogeneity induces higher dome-scale displacements and that, when there is also a discrete weakened zone, the addition of diffuse heterogeneity leads to more widely distributed deformation. Therefore, alongside discrete zones defined by different material properties, we find that the diffuse heterogeneity inherent to a dome is sufficient to compromise dome stability and should be incorporated in future modelling endeavours.

The influence of water-saturation on the strength of volcanic rocks and the stability of lava domes

“…PFC has been previously used to successfully model the mechanical behaviour of rock (e.g., Potyondy and Cundall, 2004) and, recently, to model dome growth and collapse (Husain et al, 2014(Husain et al, , 2018Harnett et al, 2018;Husain et al, 2019;Harnett and Heap, 2021;Walter et al, 2022;Heap et al, 2023a). These DEM models consider a particlebased material in which circular particles interact at interparticle contacts.…”

“…Second, modelling has shown that the mechanical properties of dome-and edifice-forming rock plays a first-order role in dictating their stability and therefore the risk of collapse and associated hazards (Apuani et al, 2005;Reid et al, 2001;Moon et al, 2009;Borselli et al, 2011;Schaefer et al, 2013;Heap et al, 2021a, b;Harnett and Heap, 2021;Wallace et al, 2022;Mordensky et al, 2022;Harnett et al, 2022;Carr et al, 2022;Heap et al, 2023a) and so, if water-saturation reduces rock strength, it must also decrease dome and edifice stability.…”