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This workshop served to assess the main advantages and shortcomings of existing eruption classification schemes and to identify open questions and research priorities that could help improve our understanding of volcanic explosive eruptions. We identified the main parameters and processes characterizing volcanic eruptions that include initial conditions, conduit related magma dynamics, eruptive processes and parameters, external factors. We reviewed most existing "general" classification schemes (i.e., those that are not based on specific volcanoes) in order to identify major shortcomings and most widely used terminology. We found that all existing classification schemes fail to collate all volcanic eruptions in one simple diagrammatic form, and do not account for all volcanic behaviours and products.
We concluded that: i) classification schemes need to be objective focused and driven (e.g. scientific understanding, hazard/risk assessment, communication with public, civil defence institutions and scientific community) and simple enough to promote transfer of knowledge and scientific exchange; ii) classification should be based on clearly defined observables, and aimed at identifying the main processes. We found that most existing classification schemes are based on processes (e.g. Walker 1973, 1980; Pyle 1989; Bonadonna and Costa 2013) but the parameters do not capture all volcanic phenomena and are too broad to distinguish between transient versus sustained eruptions or steady versus unsteady behaviours; iii) classification schemes should be comprehensive and encompass a variety of eruptive styles and volcanic products, including for example, lava flows, PDCs, gas emissions and cinder cone or caldera formation; iv) currently we do not have a system that can be used for all eruptions. It might be possible in the future to have a more comprehensive classification scheme, but it is more likely that it will be associated with a different way of measuring eruptions (e.g. energy balance) instead of evolving from existing schemes; v) none of the existing schemes consider the distinction between steady and unsteady processes. We identified that unsteadiness is, in fact, a key factor for describing volcanic eruptions, but also concluded that we do not yet have effective means of classifying unsteadiness itself. Future eruption classification schemes should incorporate the concept of unsteadiness; vi) open questions, processes and parameters that need to be addressed and better characterised in order to develop more comprehensive classification schemes and to progress in our understanding of volcanic eruptions include: abrupt transitions in eruption regime, conduit processes and dynamics, unsteadiness, eruption energy, and energy balance.
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