Elicitation of potential future explosive silicic eruption scenarios at Corbetti and Aluto volcanoes, Ethiopia

This report describes an expert elicitation on the recurrence rates of potential future explosive silicic eruptions at Corbetti and Aluto volcanoes in the Main Ethiopian Rift (MER) and their uncertainties. This work represents BGS national capability support for research the BGS Volcanology team is leading in the RiftVolc project on future volcanic hazards in the MER.
Field campaigns have contributed to a step-change in knowledge from 2015 when the Global Assessment of Risk report (GAR15) highlighted the lack of data on volcanoes in Ethiopia (Brown et al., 2015). New data acquired through the RiftVolc project have increased our understanding of past volcanism and magmatism, particularly at Aluto and Corbetti central volcanoes in the MER. However, the data and knowledge are still limited, constrained by a lack of dateable material and resources to map and correlate volcanic deposits at these complex volcanoes.
In RiftVolc, we are developing several approaches to better understand hazards and the associated uncertainties. A key part of our planned tephra fall hazard assessment requires a judgement of the likely characteristics and recurrence intervals of future explosive silicic eruptions. Such inferences are at least partly reliant on eruption histories derived from the recent RiftVolc geological and geochronological fieldwork (e.g. Fontijn et al., 2018; McNamara et al., 2018; Siegburg et al., 2018). In addition, to support the development of event trees for probabilistic hazard assessment, we need to explore the probabilities of occurrence of particular eruptive scenarios. In order to meet both of these objectives, we have elicited the judgement of a group of five experts, using the SHeffield ELicitation Framework (SHELF; Oakley and O’Hagan, 2010) method, on the recurrence rate of future explosive silicic eruptions at Aluto and Corbetti volcanoes.
The first part of the report introduces the RiftVolc project and describes the expert elicitation procedure. This includes a description of the questions to be elicited. Section 2 of the report presents the elicited distributions of individuals and the group consensus for each question, as well as a summary of discussions held by the experts, which enabled them to agree on a final distribution. The recurrence rates for potential future eruptions at Corbetti and Aluto volcanoes derived from the group distributions are provided in Section 3. Sections 4 and 5 summarise the key points raised during discussions and highlight lessons learnt which should be taken into consideration in future expert elicitations of volcanic activity. Finally, a summary and conclusions are provided in Section 6.