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While the effects of volcanism on Earth’s climate are well understood, the volcano-ice sheet system hosts a two-way feedback. Volcanic activity promotes ice melting, which in turn affects the internal dynamics of the magma chamber below. At present, accurate forecasts of sea-level rise hinge on the stability of the West Antarctic Ice Sheet, and thus require consideration of subglacial volcano-deglaciation feedbacks. The West Antarctic Ice Sheet, grounded below sea-level, is particularly vulnerable to collapse, yet its position atop an active volcanic rift is seldom considered. Ice unloading raises the geotherm and alters the crustal stress field, impacting dike propagation. However, the consequences on internal magma chamber dynamics and thus long-term eruption behavior remain elusive. Given potential for unloading-triggered volcanism in West Antarctica to accelerate ice retreat, we adapt the thermomechanical magma chamber model of Scholz et al. (2023) for West Antarctic Rift basalts, simulating a shrinking ice load through a prescribed decrease of lithostatic pressure. Examining different unloading scenarios, we investigate the impacts on volatile partitioning within the magma and eruptive trajectory across a wide range of initial magma chamber conditions. Pressurization of a magma chamber beyond a critical threshold results in eruption, delivering enthalpy to the ice. Considering the removal of km-thick ice sheets, we demonstrate the rate of unloading is dominant in influencing the cumulative mass erupted and consequently, heat released to the ice. These findings provide fundamental insights into the complex volcano-ice interactions in West Antarctica and other subglacial volcanic settings. 

Abstract Magmatic volatiles drive pressure, temperature, and compositional changes in upper crustal magma chambers and alter the physical properties of stored magmas. Previous studies suggest that magmatic H₂O content influences the growth and longevity of silicic chambers through regulating the size and frequency of eruptions and impacting the crystallinity‐temperature curve. However, there has been comparatively little exploration of how CO₂impacts the evolution of magma chambers despite the strong influence of CO₂on H₂O solubility and the high concentrations of CO₂often present in mafic systems. In this study, we integrate the thermodynamic effects of dissolved and exsolved H₂O and CO₂with the mechanics of open‐system magma chambers that interact thermally and mechanically with the crust. We applied this model to investigate how intrinsic variations in magmatic H₂O‐CO₂content influence the growth and longevity of silicic and mafic magma chambers. Our findings indicate that even with a tenfold increase in CO₂content (up to 10,000 ppm), CO₂plays a minimal role in long‐term chamber growth and longevity. While CO₂content affects the magma compressibility, the resulting changes in eruption mass are balanced out by a commensurate change in eruption frequency so that the time‐averaged eruptive flux and long‐term chamber behavior remain similar. In contrast, H₂O content strongly influences chamber growth and longevity. In silicic systems, high H₂O contents hinder magma chamber growth by increasing the total eruptive flux and steepening the slope of the crystallinity‐temperature curve. In mafic systems, high H₂O contents promote magma chamber growth by flattening the slope of the crystallinity‐temperature curve.