This talk describes a First-order System Least-squares (FOSLS) formulation of the nonlinear Stokes flow used to model glaciers and ice sheets. We use a Nested Iteration (NI), Newton-FOSLS-AMG approach in which the majority of the work is done on coarse grids. This talk will describe a new FOSLS formulations that avoids the difficulty of infinite viscosity.
In current ice sheet codes, viscosity is modeled using a formula known as Glen's law. It becomes infinite as the gradient of velocity approaches zero, which can happen near the bed and along the top surface where ice is carried undeformed. In current ice sheet codes, this is mitigated by a small modification to Glen's law that bounds the maximum value of viscosity. Infinite viscosity has has been problematic for ice sheet codes.
In this talk, a new first-order system formulation will be presented that
overcomes the difficulty of infinite viscosity. The new formulation is
well posed and 
elliptic away from spatial locations where the
gradient of velocity is zero. Numerical tests are presented which
demonstrate good performance of the NI-Newton-FOSLS-AMG