LAUSR

Abstract Hydrothermal eruptions are explosive events driven by the sudden and violent vaporization of the water present in many hot water geothermal fields worldwide. Over recent years, thermodynamical conditions of fluids and petrophisical-geomechanical features of host-rocks were mentioned as responsible of the wide range of eruptive styles and deposits of hydrothermal eruptions. Nevertheless, geological and historical records show that PDC and fallout processes are underestimated as common processes linked to hydrothermal eruptions. This paper analyzes from a multi-disciplinary approach —virtual outcrops modeling, sedimentology, petrographic and XDR studies, facies modeling, eye-witness source analysis, and stratigraphy— the pristine Holocene–historic hydrothermal eruptive record of El Humazo manifestation (Domuyo Geothermal Field, Patagonia, Argentina). Different eruptive scenarios are characterized by ballistic ejection, PDC and/or fallout mechanisms with discernible tefra-composition and granulometry, associated with both excavational and/or aggradational landforms. We show how diverse eruptive dynamics are controlled by pre-eruptive internal and external factors, such as reservoir energy, depth of the explosion/fragmentation levels, physical properties and structural anisotropy of the host-rocks and eruptive center migrations. We consider that this case study may be useful not only for the application in the assessment of the volcanic hazard associated with the Domuyo geothermal field, but also contributes to the knowledge of the eruptive dynamics in other geothermal systems with similar characteristics.