S1.17: Advances in understanding volcanic debris avalanche processes and hazards - from field studies to experimental and numerical modelling applications
The formation of volcanic debris avalanches (VDA) resulting from the failure of an unstable edifice represents the largest-magnitude hazard from active, dormant and even extinct stratovolcanoes. While these events are much less frequent than other volcanic hazards, they represent by far the most destructive scenario, involving large volumes of debris and potential travel distances of more than 100 km. The 18 May 1980 Mount St. Helens eruption, 40 years ago this month, presented the first opportunity to observe and document the generation and emplacement of a large VDA. These observations integrated with studies of the produced deposits provided a ground-breaking model for the interpretation of similar deposits elsewhere. Consequently, VDA deposits have been recorded at many volcanoes worldwide and their generation through catastrophic edifice failure is now recognised as a common, often recurring phenomenon in the life cycle of long-lived composite volcanoes. While research since the 1980 event has significantly improved our knowledge of the factors leading to volcano collapse as well as VDA transport and emplacement processes, their complex flow dynamics are still not fully understood. In particular the observed excess run out and transformation into cohesive debris flows pose challenges for accurate numerical modelling and similarly, more precise input parameters are required for the development of realistic hazard models. We invite contributions from field, experimental and modelling approaches focused on advances in understanding volcanic instability, trigger mechanisms of catastrophic edifice failure, VDA transport and emplacement processes and sedimentary characteristics of the resulting deposits.Core connection between the proposed session and societal risk mitigation: While volcanic debris avalanches are typically of low frequency, they are a common process at active, dormant and even extinct composite volcanoes worldwide.Their extreme mobility and large volume make them a high-magnitude hazard with widespread, devastating impacts on communities and infrastructure in the surroundings of unstable volcanoes. Such events often occur with little warning, thus in order to mitigate future risk from debris-avalanche generating volcanic edifice failures, it is important to understand their probability and likely scale. Modelling approaches can help test various scenarios and identify areas most at risk of these catastrophic mass flows. As they rely on a range of input parameters such as the nature of past events, present-day geomorphology and up-to-date knowledge of flow dynamics, it is crucial to continue improving our multi-disciplinary understanding of debris avalanche processes.