Viscosity of silicate melts as a function of their total H
O content and temperature. (A) Hydrous andesite melt viscosity from Richet et al. (1996) recorded at ambient pressure by using a sample synthesized at 400 MPa and 1400˚C before viscosity measurement at ambient pressure and temperatures indicated. (B) Temperature-dependence of melt viscosity of granite composition with (8 wt%) and without H2O as indicated on curves from Hess and Dingwell (1996).