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Unravelling the effects of volatile resorption on eruption onset in large silicic systems

Franziska Keller1, Meredith Townsend1, Juliana Troch2, Chris Huber3

  • Affiliations: 1Department of Earth Sciences and Environmental Sciences, Lehigh University, USA, 2Division of Geosciences and Geography, RWTH Aachen University, Germany, 3Department of Earth, Environmental, and Planetary Sciences, Brown University, USA

  • Presentation type: Talk

  • Presentation time: Tuesday 16:00 - 16:15, Room S150

  • Programme No: 3.2.10

  • Theme 3 > Session 2

Abstract

Silicic caldera-forming eruptions are inherently difficult to trigger, as prolonged magma storage heats the crust and buffers the buildup of overpressure. One proposed triggering mechanism involves the exsolution of volatiles that pressurize magma chambers via volume expansion. However, exsolved volatiles also increase magma compressibility, hindering recharge-driven pressurization. Therefore, the role of exsolved volatiles in the growth and stability of large silicic reservoirs remains poorly understood. To address this gap, a study of the Aso caldera (Japan) used volatile partitioning in apatite to track water-saturation levels prior to caldera eruptions, revealing the (partial) loss of exsolved volatiles shortly before the cataclysmic Aso-4 eruption. Using a thermo-mechanical box model, we investigate how recharge-induced pressurization, crystal melting and magma mixing influence water saturation and its subsequent impact on chamber pressurization and eruption timing. Our results show that volatile resorption can occur in silicic systems that are subjected to high magma recharge rates involving drier and hotter magmas. Under these conditions, recharge increases the melt volume fraction of the resident magma through crystal melting and the addition of anhydrous melt, driving the diffusion of exsolved H2O back into the melt to maintain chemical equilibrium. If the host magma chamber loses all its exsolved volatiles, continuous recharge leads to a faster rate of chamber pressurization due to decreased magma compressibility. This rapid pressurization can trigger an eruption up to 100 years earlier than expected under similar conditions but with a residual exsolved volatile phase, posing significant challenges for assessing eruption risk at such hazardous systems.