Managing ash fall hazards from large silicic eruptions -- lessons from Patagonia

WILSON, THOMAS; STEWART, CAROL; BICKERTON, HEARTHER; LEONARD, GRAHAM S; VILLAROSA, GUSTAVO

Colima

Congreso; Cities on Volcanoes 7; 2012

Cities on Volcanoes Commission - IAVCEI

Pyroclastic fall from large silicic eruptions is one of the most significant volcanic hazards to society. The 1991 Hudson, 2008 Chaiten and 2011 Puyehue Cordón-Caulle eruptions have affected significant areas of Patagonian South America. A sustained programme of post-event impact assessment has attempted to identify common impacts and tolerances, effectiveness of mitigation actions, lessons learned and adaptive behaviours. Trips have been undertaken at varying time intervals after the eruptions. This paper presents a summary of a) societal impacts from these three eruptions, with a focus on critical infrastructure and farming and b) scientific and emergency management lessons.Impact assessment and provision of scientifically robust information and mitigation advice has been challenging in all three eruptions. It is clear that physical impacts of ash to animals, vegetation and soils are significantly more damaging than any recorded chemical toxicity; yet fears of chemical poisoning due to ash are a common and powerful anxiety and so require robust scientific analysis and communication. Remobilisation of pyroclastic material by wind and water processes create on-going impacts which require management.Lack of preparedness for ash fall hazards has exacerbated infrastructure vulnerability in many instances, however strong adaptive capacities in the aftermath of an ashfall have been commonly exhibited. The loss of critical infrastructure service due to ash fall impacts has strongly contributed to the evacuation of several towns and regions.Case studies from all three eruptions highlight the importance of coordinated and robust scientific information collection, coordination and, importantly, communication. In addition to the complexities of dealing with the volcanic eruptions, widespread distribution of ash fall creates transnational and trans-provincial emergency management issues which have required careful management. At a more general level, standardised physical and chemical ash analysis, timely and consistent assessment for impact assessment and recovery strategy recommendations, and on-going ashfall preparedness actions for all sectors are strong lessons for future Patagonian eruptions and beyond