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Bringing Together Scientific and Community Knowledge to Improve Assessment of Lahar Impacts in St. Vincent

Rachel Clark1 , Jeremy Phillips1, Jenni Barclay1, Richard Robertson2.

  • Affiliations: 1School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, UK. 2The University of the West Indies, Seismic Research Centre, St Augustine, Trinidad and Tobago, West Indies.

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 57

  • Programme No: 6.3.16

  • Theme 6 > Session 3

Abstract

The 2020 -- 21 eruption of La Soufrière, St. Vincent expelled substantial volcanic debris on its flanks. During heavy rainfall events, these are remobilised as lahars, posing serious threat to infrastructure and communities. While patterns of occurrence have changed since the eruption, lahars remain a significant hazard, so up-to-date hazard maps on lahar model predictions are crucial. Using the dynamic model LaharFlow (www.laharflow.bris.ac.uk/), we present new predictions of damage to roads and bridges, as well as to offshore communication cables by estimating fluxes of sediment and water transported to the ocean during lahar events. We also assess the consequences of engineered mitigation strategies, such as recent boulder-lining of certain northeastern river channels. Through rainfall analysis, combined with simplified catchment hydrology, and lahar observations, we present a new approach for scenario selection for lahar hazard mapping, and new model estimates of lahar arrival times. Simulated lahar depths and speeds align well with flow observations on the coastal areas of St. Vincent. Most of the lahar observations were provided by the 'Changing Landscapes' project, which supported communities in the northeast of St. Vincent to document changes after the 2021 eruption. These observations are critical for understanding how lahars have changed since the 2021 eruption. Initial meetings with the National Emergency Management Organisation (NEMO) and National Met Services have identified a pathway for using these community observations and model results in national hazard mapping, and we discuss the benefits to both communities and government agencies of bringing this knowledge together.