Operating the Aviation Color Code system at European Volcano Observatories: experiences and challenges

Volcano Observatories (VOs) around the world are required to maintain the surveillance of their volcanoes and inform timely civil protection and aviation authorities about impending eruptions. Often, they work through procedures which allow them to respond timely to volcanic crises and provide a service aimed at reducing the potential impact of an eruption. Within the International Airways Volcano Watch (IAVW) framework, VOs are asked to operate a system designed to inform the aviation community about the status of a volcano and the expected threat associated. Despite the IAVW documentation reports the definition of the different color coded levels, operating the Aviation Color Code (ACC) can be a difficult task and VOs might adopt different strategies on how, when and why to change it. Following the two European Volcano Observatories and VAACs meetings, in 2019 and 2021, the European VOs agreed to present an overview on how they work about ACC. This analysis reveals that not all VOs in Europe have the usage of ACC as part of their operations, mainly because of lack of eruptions in recent times. Moreover, those VOs which regularly adopt ACC, operate it differently depending on the frequency of the eruptions, the type of volcano, the historical eruptive activity, the monitoring level, but also the agreement with the local Air Transport Navigation providers. At the same time all VOs change ACC in a very dynamic way to reflect the variability in the volcanic activity, except during decreasing activity and waning phase. This study shows that despite the ACC system is designed to provide a standard, its usage strongly depends on the evaluation of those responding to volcano emergencies. Still the usage of ACC is of relevance for the aviation stakeholders, that encourage its practice in addition to a wider dialogue with the Volcano Observatories in Europe.