Development of a volcanic hazard assessment methodology in low-data environments: Ascension Island, South Atlantic

Knowledge of the character, frequency, magnitude and impacts of previous eruptions from historical records and geological data is in many cases insufficient to enable comprehensive volcanic hazard and impact assessments. Volcanic islands often have only sparse geological data due to a combination of poor exposure, poor deposit preservation, remote location, small physical size of the island, or a lack of resources to carry out the required fieldwork. Inhabitants of small isolated islands, such as the UK Overseas Territories in the South Atlantic, are exposed to multiple natural hazards and the effects of climate change, leading to increasing risks. However, there are limited options for early warning or timely self-evacuation in the event of a crisis. We present the development of a volcanic hazard assessment methodology for low data environments using an analysis carried out for Ascension Island in the South Atlantic as a case study. Using a combined approach of the available geological data, co-development of scenarios with the Ascension Island Government, expert elicitation, consideration of uncertainties, and the application of an eruption analogue to parameterise hazard models, we have carried out probabilistic vent-opening and tephra fall hazard analyses, as well as lava flow modelling. The probabilistic hazard maps form the evidence base to enable discussions with stakeholders on potential future volcanic activity and impacts.