  Here we propose a simple modification of the parameterisation presented in
Costa (2005) [Viscosity of high crystal content melts: dependence on solid
fraction, Geophys. Res. Lett., 32, 2005] which improves all the main positive
features of it, yet at the same time, does not show a plateau region as the
solid fraction tends to 1, generally increases the performance of the model,
and exactly recovers the classical well established relationships valid for
small fractions.
