A volcano alert level system (VALS) forms a key component of a volcano early warning system, which is used to communicate warning information from scientists to civil authorities managing volcanic hazards. In 2006, the United States Geological Survey (USGS) standardised its VALS, replacing all locally developed systems with a common standard. The emergence of this standardisation, and resulting implications, are charted here, in the context of managing the scientific complexities and diverse agencies involved in volcanic crises. The VALS concept embodies a linear reductionist approach to decision-making, designed around warning levels that correspond to levels of volcanic activity. Yet, complexities emerge as a consequence of the uncertain nature of the physical hazard, the contingencies of local institutional dynamics, and the plural social contexts within which each VALS is embedded, challenging its responsiveness to local knowledge and context. Research conducted at five USGS managed volcano observatories in Alaska, Cascades, Hawaii, Long Valley, and Yellowstone explores the benefits and limitations standardisation brings to each observatory. It concludes that standardisation is difficult to implement for three reasons. Firstly, conceptually, natural hazard warning systems are complex and non-linear, and the VALS intervenes in an overall system characterised by emergent properties and the interaction of many agents, for which forecasting and prediction are difficult. Secondly, pragmatically, the decision to move between alert levels is based upon more than volcanic activity and scientific information, with broader social and environmental risks playing a key role in changing alert levels. Thirdly, empirically, the geographical, social and political context to each volcano observatory results in the standardised VALS being applied in non-standard ways. It is recommended that, rather than further defining a standardised linear product, VALS should focus on developing systems based upon processes and best practice designed to facilitate communication and interaction between scientists and users in context
