Water in volcanoes: evolution, storage and rapid release during landslides

Abstract

Volcanoes can store and drain water that is used as a valuable resource by populations living on their slopes. The water drainage and storage pattern depend on the volcano lithologies and structure, as well as the geological and hydrometric settings. The drainage and storage pattern will change according to the hydrometric conditions, the vegetation cover, the eruptive activity and the long- and short-term volcano deformation. Inspired by our field observations and based on geology and structure of volcanic edifices, on hydrogeological studies, and modelling of water flow in opening fractures, we develop a model of water storage and drainage linked with volcano evolution. This paper offers a first-order general model of water evolution in volcanoes. The volcano’s water plays an important role in volcano stability and instability. Nevertheless, the migration and storage of volcanic water prior and during landslide have not been extensively studied in regard to volcano evolution. We further explore this role and its impact on debris avalanche emplacement behaviour. Isolated water-saturated domains will favour ductile deformation, and unequal distribution of water within the debris avalanche partly explains the coeval occurrence of brittle and ductile deformation, indicating complex rheologies, and varied emplacement mechanisms. If the volcano prior to landslide is storing large amounts of water, this water will quickly flow in the landslide and will form a basal slurry upon which the avalanche will spread further.