Probabilistic hazard analyses for a small island: methods for quantifying tephra fall hazard and appraising possible impacts on Ascension Island

Osman, Sara; Crummy, Julia; Thomas, Mark; Carver, Stephen. 2024 Probabilistic hazard analyses for a small island: methods for quantifying tephra fall hazard and appraising possible impacts on Ascension Island. Bulletin of Volcanology, 86 (10), 82. https://doi.org/10.1007/s00445-024-01771-3

Before downloading, please read NORA policies.

Preview

Text (Open Access Paper) s00445-024-01771-3.pdf - Published Version Available under License Creative Commons Attribution 4.0. Download (8MB) | Preview

Abstract/Summary

Proximal to the source, tephra fall can cause severe disruption, and populations of small volcanically active islands can be particularly susceptible. Volcanic hazard assessments draw on data from past events generated from historical observations and the geological record. However, on small volcanic islands, many eruptive deposits are under-represented or missing due to the bulk of tephra being deposited offshore and high erosion rates from weather and landslides. Ascension Island is such an island located in the South Atlantic, with geological evidence of mafic and felsic explosive volcanism. Limited tephra preservation makes it difficult to correlate explosive eruption deposits and constrains the frequency or magnitude of past eruptions. We therefore combined knowledge from the geological record together with eruptions from the analogous São Miguel island, Azores, to probabilistically model a range of possible future explosive eruption scenarios. We simulated felsic events from a single vent in the east of the island, and, as mafic volcanism has largely occurred from monogenetic vents, we accounted for uncertainty in future vent location by using a grid of equally probable source locations within the areas of most recent eruptive activity. We investigated the hazards and some potential impacts of short-lived explosive events where tephra fall deposits could cause significant damage and our results provide probabilities of tephra fall loads from modelled events exceeding threshold values for potential damage. For basaltic events with 6–10 km plume heights, we found a 50% probability that tephra fallout across the west side of the island would impact roads and the airport during a single explosive event, and if roofs cannot be cleared, three modelled explosive phases produced tephra loads that may be sufficient to cause roof collapse (≥ 100 kg m−2). For trachytic events, our results show a 50% probability of loads of 2–12 kg m−2 for a plume height of 6 km increasing to 898–3167 kg m−2 for a plume height of 19 km. Our results can assist in raising awareness of the potential impacts of tephra fall from short-lived explosive events on small islands.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1007/s00445-024-01771-3
ISSN:	1432-0819
Date made live:	21 Nov 2024 17:15 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/538416

Actions (login required)

View Item

Document Downloads

More statistics for this item...