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Addressing the challenges and knowledge gaps in reconstructing eruptive behaviour in volcanic island settings

Sebastian Watt , Mike Cassidy

Abstract

A major proportion of Earth's volcanoes lie in island settings: 43% of the global arc length comprises island volcanoes, alongside numerous rift and intraplate volcanic islands. Hazards posed by these volcanoes are modified by interactions with water, and the scale of their eruptions is diverse, with island sites likely responsible for many of the largest Holocene eruptions. Volcanic islands also present challenges for monitoring and hazard mitigation, given reduced scope for ground- and satellite-based observations, and often isolated communities or fragmented communication networks. Such settings thus warrant attention, yet our capacity to reconstruct past behaviour at island volcanoes -- information vital to more informed risk management strategies -- is directly hindered by their geographic environment. Subaerial exposures are limited, and submarine archives of past activity, which may be more complete than in many continental environments, are challenging to access. This has led to a significant information gap: in many parts of the western and southern Pacific, knowledge of Holocene eruptions is over two orders of magnitude lower than that in well-studied continental areas, on a regional scale, and effectively absent for many areas. Here, we explore these challenges using a variety of case studies, with a particular focus on Indonesia and the SW Pacific. The complexity of eruptive behaviour, and the potential for cascading hazards, is connected to island size. In turn, this presents difficulties for reconstructing past activity and for sampling and interpreting deposits, calling for new strategies to evaluate past activity and address broader knowledge gaps.