From alteration to avalanche: A 3D framework for exploring hydrothermal weakening of lava domes

Volcanic domes are inherently unstable structures that form when lava is too viscous to flow away from the vent. Dome collapse poses a hazard via volcanic landslides and debris avalanches that can threaten nearby communities. Dome collapse can be promoted by hydrothermal alteration, which can weaken volcanic rock and is commonly concentrated in regions with high fluid flow, such as fractures and areas of high permeability within the dome. Here, we focus on understanding how alteration affects dome stability, collapse volumes and runout distances, using the case study of La Soufrière de Guadeloupe, in the Eastern Caribbean. We present new 3D models that combine geophysical and mechanical data to investigate different post-emplacement dome stability scenarios that incorporate hydrothermal alteration. Our results demonstrate that increased alteration-induced weakening (i.e., to 50% or 10% of the original rock strength) leads to greater displacements and causes dome destabilisation. Additionally, we show displacement and finite shear strain as a result of varying the spatial extent (the thickness and location) of the alteration zones. We also show that incorporating mechanical heterogeneity is crucial for accurate hazard modelling. We introduce a novel method using the La Soufrière de Guadeloupe dome to offer a comprehensive understanding of the alteration process from initiation to deposit. Our results indicate that hydrothermal alteration significantly increases collapse volumes and thus, runout distances, which are critical for understanding the potential impact of dome collapse and a critical motivation for our 3D modelling approach. By capturing the full process from internal weakening to hazard potential, this method enhances our ability to anticipate future dome collapse events, and thus, mitigate their effects.