Hydrothermally altered rocks of La Fossa, Vulcano island (Italy): Implications for flank instability from coupled drone photogrammetry and rock mechanical measurements

Hydrothermal alteration is well recognized to change the physical and mechanical properties of volcanic rocks and promote instability and flank collapse. Here, we investigate La Fossa of Vulcano Island (Italy), the southernmost exposure of the Aeolian volcanic archipelago, and its associated regions of hydrothermal alteration. La Fossa’s accessibility, altered flanks, history of mass wasting events, and periods of escalating fumarole activity set an ideal environment for a natural laboratory. We used drone remote sensing methods coupled with field and ongoing laboratory rock property measurements to classify regions of hydrothermal alteration and assess their associated rock properties. Our results have (1) identified a heterogenous distribution of alteration intensity and alteration types, (2) distinguished a relationship between decreasing rock strength and increasing alteration, and (3) correlated regions with the weakest rock strength with hydrothermally altered flanks. This combined approach allows us to explore the relationships between hydrothermal alteration, rock strength, and flank instability of La Fossa.