Source: Geochemistry, Geophysics, Geosystems
In a new study, Yip et al.  compile observations of all subaerial basaltic eruptions since 2005, a period when satellite coverage has been sufficient to test whether each eruption exhibited degassing of magmatic SO2 (a readily-observed proxy for the more abundant magmatic gases H2O and CO2) and whether each eruption was associated with deformation (inflation or deflation) of the ground surface. They find that volatile-rich eruptions, which tend to occur at arc volcanoes, are (surprisingly) much less likely to be accompanied by ground deformation. By contrast, relatively volatile-poor eruptions at ocean island volcanoes are much more likely to show ground deformation.
The authors develop a thermodynamic model of magma degassing and physical properties that emphasizes the role of bubbles in increasing the compressibility of the magma plumbing system, which leads to a surprising new theory and prediction for whether ground deformation will occur. Bubble-rich plumbing systems, they find, are more compressible, and this has the effect of strongly suppressing the stresses that leads to ground deformation.
Citation: Yip, S. T. H., Biggs, J., Edmonds, M., Liggins, P., & Shorttle, O. (2022). Contrasting volcanic deformation in arc and ocean island settings due to exsolution of magmatic water. Geochemistry, Geophysics, Geosystems, 23, e2022GC010387. https://doi.org/10.1029/2022GC010387
—Paul Asimow, Editor, Geochemistry, Geophysics, Geosystems