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From Cause to Hazard: Assessing Alteration-Induced Instability in Volcanic Domes

Kendra Ní Nualláin1, Claire E. Harnett1, Alexis Hyrsiewicz1, Michael J. Heap2, Thomas R. Walter3

  • Affiliations: 1UCD School of Earth Sciences, University College Dublin, Dublin, Ireland 2Université de Strasbourg, CNRS, Institut Terre et Environnement de Strasbourg Strasbourg, France 3GFZ German Research Centre for Geosciences, Potsdam, Germany 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 37

  • Programme No: 3.8.21

  • Theme 3 > Session 8

Abstract

Volcanic domes are unstable structures due to their incremental growth, varying extrusion rates, and diverse material properties. Domes frequently collapse due to factors such as hydrothermal alteration. Hydrothermal fluids interact with volcanic rocks, altering their physical and chemical properties and often results in mechanical weakening. Thus, domes commonly collapse and generate turbulent avalanches of material, threatening communities and influencing the volcano's eruptive dynamics. The internal structure of the La Soufrière de Guadeloupe dome has been mapped using geophysical methods to obtain rock density variation within the dome. Density contrasts were correlated with mechanical parameters to obtain a 3D strength map of the volcano. We input this data into large-scale 3D models that employ the Discrete Element Method. Scenario testing evaluates how changes in the location, intensity, and extent of alteration affect dome stability. We calculate alteration-induced displacement and strain, and therefore suggest the potential for large-scale collapse given varied alteration scenarios. More pervasive alteration (weakening rock to 10% of its original strength) and broader spatial extent (150 m thick zone over the southern flank) leads to larger collapse volumes. We compare these results with alteration scenario testing for a homogeneous model, i.e. if geophysical data were unavailable. Models with material heterogeneity result in displacements an average of 53 times their homogeneous counterpart. at a 10 cm threshold, and further compromise dome stability. We input our results into 'VolcFlow' to estimate collapse runout distances and discuss the severity of alteration-induced collapse hazard for the island of Guadeloupe to mitigate future risk.