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Abstract Water and carbon dioxide are the most abundant volatile components in terrestrial magmas. As they exsolve into magmatic vapour, they promote magma buoyancy, accelerating ascent and modulating eruptive dynamics. It is commonly thought that an increase in pre-eruptive volatile content produces an increase in eruption intensity. Using a conduit model for basaltic eruptions, covering the upper 6 km of conduit, we show that for the same chamber conditions mass eruption rate is not affected by CO2content, whereas an increase in H2O up to 10 wt.% produces an increase in eruption rate of an order of magnitude. It is only when CO2is injected in the magma reservoir from an external source that the resulting pressurisation will generate a strong increase in eruption rate. Results also show that ascent velocity and fragmentation depth are strongly affected by pre-eruptive volatile contents demonstrating a link between volatile content and eruptive style.
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Investigating the Impact of an Exsolved H 2 O‐CO 2 Phase on Magma Chamber Growth and Longevity: A Thermomechanical Model
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.
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- Award ID(s):
- 2444709
- PAR ID:
- 10480434
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 24
- Issue:
- 12
- ISSN:
- 1525-2027
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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