Volcanoes are heterogeneous and unstable structures prone to collapse and, as such, they present a physical and economic risk to the population living in their proximity. Hydrothermal alteration, common to many volcanoes, changes rock strength and is thought to be involved in the process of stability decrease. To understand the stability of volcanoes, large-scale numerical models incorporate petrophysical and mechanical parameters that have been measured in the laboratory. Point load testing, on the other hand, is a field technique that can quickly measure a large sample suite, which removes the challenges associated with rock transportation or selecting appropriate samples that accurately reflect the heterogeneity of the volcanic structure. Therefore, we tested almost 550 rocks from seven different locations on La Soufrière de Guadeloupe, an active andesitic stratovolcano in the Eastern Caribbean. We chose to collect irregular-shaped rocks, from 35 to 85 millimetres in height. We sampled four landslides on the flanks of the dome that exhibited different alteration intensities, two fumaroles at the summit of the dome, and a large fault on the side of the volcano. The rocks were assigned an alteration grade value depending on the visible intensity of the alteration, using parameters such as colour and rock texture. After measuring the bulk rock density of each rock using the Archimedes density method, they were broken in a point load tester. We observed that strength increases with the increase in bulk rock density. We also observed a large range in strength for a given density, highlighting the heterogeneity of the sample suite. For example, at a bulk density of around 2000 kg/m3, we noticed that the breaking force can vary between 0,43 and 9,66 kN. Also, rocks that were assigned with higher alteration grades were found to be less dense and weaker. Point load testing can provide a deeper understanding of the heterogeneity of the volcano and spatial strength distributions to improve large-scale volcano stability modelling, hence helping monitor volcanic unrest and mitigate future risks.
