Morpho-structural criteria for the identification of spreading-induced deformation processes potentially compromising stratovolcano stability

Abstract

Characterisation of surface deformation at stratovolcanoes is essential for a better understanding of the processes that can compromise edifce structural stability and potential for fank collapse. Spreading produced by the presence of a hydrothermal system or intrusion of a viscous magma body can produce similar deformation signatures, and both processes have implications for fank instability. In this work, we perform analogue models and consider examples from real volcanoes (Damavand, Ubinas, Semeru and Casita) so as to characterise and recognise surface deformation patterns produced by spreading due to the presence of a hydrothermal system and in response to magma intrusion. The experiments show that there are diferences in the resulting surface deformation associated with each process. Magma intrusion results in a sharp transition between areas of subsidence and uplift, and is associated with faults with oblique strikes in the upper part of the edifce. Instead, asymmetric fank spreading is associated with hydrothermal system and results in fank bulging close to the base of the edifce. Although laboratory analogue models show diferent deformation responses that could be diagnostic of the associated processes, application in the feld is difcult as often these diagnostic features are not preserved during evolution. However, basal bulging represents a potential diagnostic for the identifcation of asymmetric volcano fank spreading associated with hydrothermal activity, and the potential for instability. Remote sensing techniques can allow identifcation of such surface deformation features, providing a useful tool for hazard assessment and design of monitoring strategies at potentially unstable volcanoes.