A note on gas segregation in dykes and sills at high volumetric gas fractions

The model of gas segregation in volcanic systems developed by Menand and Phillips [Menand, T., Phillips, J.C., 2007. Gas segregation in dykes and sills. J. Volcanol. Geotherm. Res. 159, 393–408] show that non-vertical elements of the plumbing systems, such as dykes and sills, act as strong gas segregators and can explain the persistent degassing displayed by many basaltic volcanoes as well as their associated eruptive characteristics. However, this model is based on laboratory experiments carried out at low volumetric gas fractions < 10%. We present additional laboratory experiments which show that the processes governing gas segregation at high volumetric gas fractions are identical to those occurring at low gas fractions, except that higher gas fractions lead to an increase of the viscosity of the bubbly fluid and thus increase the time scales associated with gas segregation. We show that the theory developed by Menand and Phillips [Menand, T., Phillips, J.C., 2007. Gas segregation in dykes and sills. J. Volcanol. Geotherm. Res. 159, 393–408], originally valid at low volumetric gas fractions, can be extended to high gas fractions, at least as high as 40% by volume.