Water is typically the major volatile component in magmas and can reach concentrations up to ~6–7 wt. % in silicic magma chambers (e.g., see Blake
1984; Clemens
1984). When magmas migrate from their source up towards the Earth surface,
water exsolution can result in large (up to several orders of magnitude) increases in magma viscosity because of the strong effect of water on the viscosity of silicate melts (Leonteva
1940; Saucier
1952; Friedman et al.
1963; Shaw
1963; Dingwell et al.
1996; Richet et al.
1996).
Water exsolution is also accompanied by the formation of vapor bubbles that participate in decreasing the bulk density of the magma, reinforcing, in this way, the buoyant force that pushes the magma out of the Earth crust.