EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Evolution of mechanical properties of lava dome rocks across the Soufrière Hills eruption, and application in discrete element models

Claire Harnett1, Jackie Kendrick2, Anthony Lamur2, Mark Thomas3, Adam Stinton4, Paul Wallace2, and Yan Lavallee2
Claire Harnett et al.
  • 1UCD School of Earth Sciences, University College Dublin, Dublin, Ireland.
  • 2Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool, UK.
  • 3School of Earth and Environment, University of Leeds, Leeds, UK.
  • 4Montserrat Volcano Observatory, Flemmings, Montserrat.

Lava dome collapses pose a hazard to surrounding populations, but equally represent important processes for deciphering the eruptive history of a volcano. Models examining lava dome instability rely on accurate physical and mechanical properties of volcanic rocks. Here we focus on determining the physical and mechanical properties of a suite of temporally-constrained rocks from different phases of the 1995–2010 eruption at Soufrière Hills volcano in Montserrat. We determine the uniaxial compressive strength, tensile strength, density, porosity, permeability, and Young’s modulus using laboratory measurements, complemented by Schmidt hammer testing in the field.

By viewing a snapshot of each phase, we find the highest tensile and compressive strengths in the samples attributed to Phase 4, corresponding to a lower permeability and an increasing proportion of isolated porosity. Samples from Phase 5 show lower compressive and tensile strengths, corresponding to the highest permeability and porosity of the tested materials. Overall, this demonstrates a reliance of mechanical properties primarily on porosity, however, a shift toward increasing prevalence of pore connectivity in weaker samples identified by microtextural analysis demonstrates that here pore connectivity also contributes to the strength and Young’s Modulus, as well as controlling permeability. The range in UCS strengths are supported using Schmidt hammer field testing. We determine a narrow range in mineralogy across the sample suite, but identify a correlation between increasing crystallinity and increasing strength. We correlate these changes to residency-time in the growing lava dome during the eruption, where stronger rocks have undergone more crystallization. In addition, subsequent recrystallization of silica polymorphs from the glass phase may further strengthen the material.

We incorporate the variation in physical and mechanical rock properties shown within the Soufrière Hills eruptive into structural stability models of the remaining over-steepened dome on Montserrat, considering also the possible effect of upscaling on the edifice-scale rock properties, and the resultant dome stability.

How to cite: Harnett, C., Kendrick, J., Lamur, A., Thomas, M., Stinton, A., Wallace, P., and Lavallee, Y.: Evolution of mechanical properties of lava dome rocks across the Soufrière Hills eruption, and application in discrete element models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14016,, 2020


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