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First geochemical characterisation of shallow pre-eruptive magma degassing at Marapi volcano, Sumatra

Charlotte Barrington 1, Hilma Alfianti2, Ugan Boyson Saing2, Patrick Allard1,3, Philipson Bani4, Fidel Costa1,3,5, Benoit Taisne1,5

  • Affiliations: 1Earth Observatory of Singapore, Nanyang Technological University, Singapore, Singapore; 2Center for Volcanology and Geological Hazard Mitigation, Geological Agency, Ministry of Energy and Mineral Resources, Bandung, Indonesia; 3Institut de Physique du Globe de Paris, Université Paris Cité, Paris, France; 4Institut de Recherche pour le Developpement, l\'Université Clermont Auvergne, Clermont-Ferrand, France; 5Asian School of the Environment, Nanyang Technological University of Singapore, Singapore 

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 246

  • Programme No: 3.17.25

  • Theme 3 > Session 17

Abstract

Marapi volcano, the most active in Sumatra, is characterised by recurrent short-lived explosions and occasional sustained, month-long eruptions, often preceded by limited geophysical precursors. Despite extensive monitoring efforts, our understanding of the processes and triggering mechanisms behind eruptions at Marapi remains limited, particularly due to insufficient knowledge of its gas fluxes and compositions, and how they change over time. To address this problem, we conducted several measurements of Marapi's volcanic gases, which also represent the first documented CO₂/SO₂ ratio for a Sumatran volcano and provide evidence of low sulfur content in volcanic emissions along the Sunda Arc. We used a Multicomponent Gas Analyser System (Multi-GAS) to measure the gases at the active Verbeek crater during two field campaigns between eruptions in 2014 and 2018. Both data sets reveal intermittent pulse-like degassing with a composition typical of gases from arc magma. Notably, the dataset collected just one month before the explosive eruptions on 27 April and 2 May 2018 shows a SO₂/H₂S molar ratio similar to 2014, but a CO₂/SO₂ ratio that is three times lower. This chemical shift is due to an increase in total sulfur relative to CO₂, and suggests shallower magma degassing in the weeks leading up to the two explosive eruptions. Our findings underscore the necessity for routine---and ideally permanent---gas monitoring at Marapi volcano to enhance our understanding of the magmatic processes driving its eruptions.