Using a discrete element approach to model lava dome emplacement and collapse

Claire E Harnett,Mark E Thomas,Matthew D Purvance,Jurgen Neuberg

doi:10.1016/j.jvolgeores.2018.06.017

Claire E Harnett, Mark E Thomas + Show 2 more

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https://doi.org/10.1016/j.jvolgeores.2018.06.017

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Abstract

Lava dome collapses can lead to explosive activity and pyroclastic flow generation which makes them one of the most deadly consequences of volcanic activity. The mechanisms linked to a collapse are however still poorly understood and very few numerical models exist that investigate the actual collapse of a lava dome after emplacement. We use a discrete element method implemented in the modelling software Particle Flow Code to investigate lava dome growth, but also go further to test the stability of the dome under the following conditions: increased internal pressure; switch in extrusion direction caused by partial cooling of the dome; and extrusion of lava onto variable underlying topography. We initially show the morphology development of a growing lava dome, and how the rheological boundary between core and talus evolves throughout the lifetime of a dome and with varied solidus pressures. Through visualisation of strain accumulation within the lava dome we show superficial rockfall development due to interaction with topography, whereas large deep-seated failures occur when the dome is exposed to internal overpressures. We find that a switch in extrusion direction promotes a transition from endogenous to exogenous dome growth and leads to lava lobe formation. We demonstrate that lava dome collapse exhibits many features similar to common landslides and by investigating strain patterns within the dome, we can use numerical modelling to understand features that elude field observations.

Highlights

Lava domes form when magma extrudes from a vent and piles up due to its high viscosity
The stability of a lava dome is affected by multiple factors including but not limited to: gravitational collapse due to over-steepening (Swanson et al, 1987); internal gas overpressures (Elsworth and Voight, 2001; Sparks, 1997; Voight and Elsworth, 2000); interaction with intense rainfall (Carn et al, 2004; Elsworth et al, 2004; Matthews et al, 2002; Taron et al, 2007); a switch in extrusion direction (Loughlin et al, 2010); topography underlying the dome (Voight et al, 2002); hydrothermal alteration (Ball et al, 2015); and the fracture state of the dome, both small-scale due to dynamic and explosive dome growth (e.g. Darmawan et al, 2018) and large scale from local tectonic faulting (e.g. Walter et al, 2015)
We find that despite the complex conditions that exist during active lava dome growth, lava domes appear to behave in many ways to traditional landslides – events that are commonly easier to observe than lava dome collapses

Summary

Introduction

Lava domes form when magma extrudes from a vent and piles up due to its high viscosity. Collapse of a lava dome can generate rockfalls, debris avalanches, and pyroclastic flows. Despite this significant hazard, relationships between active dome extrusion and collapse processes are still not entirely understood (Calder et al, 2002; Voight, 2000). Blake, 1990; Watts et al, 2002), ranging from "pancake" domes, coulées, and lava lobes (generally wide and low in height) to Peleean or blocky domes, which have a more extensive talus apron and are taller for a given radius (Blake, 1990). The domes modelled in this paper are analogous to blockier domes, rather than “pancake” domes or coulées

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