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The open-system degassing of magma controls the bifurcation of explosive and non-explosive volcanism. Permeable gas flow through connected bubbles is a potentially important mechanism of open-system degassing from viscous silicic magma. However, recent experimental study revealed that the permeability of isotropically vesiculated magma is low; this suggests that effective degassing for causing effusive eruptions requires some other mechanisms that increase the magma permeability. In this study, we experimentally demonstrate that magma deformation results in an increase in the permeability of vesiculated magma. Torsional deformation experiments of vesiculated rhyolitic melts were performed at shear strain rate of <0.029 s⁻¹ up to a total strain of 34.6; then, the permeability of the run products was measured to quantify the degassing rate. The experimental results show that shear deformation …