Presentation by Leo van der Laat.
Crater-Lake Control on Phreatic Eruptions at Poás Volcano Revealed by Seismo-Acoustic and Multidisciplinary Monitoring
Phreatic eruptions at crater-lake volcanoes are among the most hazardous and least predictable volcanic phenomena because they originate within shallow, rapidly evolving hydrothermal systems. Poás Volcano provides an exceptional natural laboratory to investigate these processes. The volcano hosts a hyperacid crater lake and is monitored by a dense network developed through collaboration between local observatories (OVSICORI–UNA and RSN–UCR) and international partners, including VDAP and the AVERT project. Broadband seismic monitoring has expanded since 2012, producing a 14-year record of activity, while infrasound monitoring began in 2019 and was strengthened in 2024 with the installation of an infrasound array through international collaboration during the 2024 AVERT workshop. In this seminar I focus on the run-up and evolution of the 2023-–2024 phreatic eruptive period using a five-year multiparametric dataset integrating crater-lake volume, gas emissions, seismic tremor, ground deformation, and infrasound observations. Trends between 2020 and 2022 indicate progressive sealing of the shallow hydrothermal system, followed by a reversal in 2022 that preceded renewed activity. During the 2023–2024 eruption, eruptive style evolved systematically as lake level decreased, producing distinct eruption types and systematic changes in infrasound signals consistent with decreasing water-column height. These observations provide new insights into how crater lakes modulate phreatic activity and illustrate how integrated monitoring can improve interpretation of hydrothermal unrest and volcanic hazard assessment.
