Ill-posedness of the shallow-ice approximation when modelling thermoviscous instabilities

A recent paper by Reference CalovCalov and others (2010) presents an intercomparison of several numerical ice-sheet models where the development of large-scale thermo-viscous instabilities is compared. In all but one of the models, the mechanics are approximated using the shallow-ice approximation (SIA). My purpose in writing this letter is to point out the dangers of using this approximation in this kind of analysis. [...]

Details