In Elmer/Ice, the dynamics of the grounding line is treated as a contact problem between the bedrock and the ice. We didn't use the floating hypothesis to determinate the GL position, neither we impose a Schoof type condition at the GL.

Many solvers and user functions are required to solve this complex problem. Here is a flowchart of the SIF file required to solve for the GL dynamics.

• 1/ GroundedSolverInit: initialise the GroundedMask variable (+ 1 if grounded, - 1 if floating, 0 if on the grounding line (also grounded but allow to localise the GL))
• 2/ Compute the Normal vector only where the ice is grounded. This is done by setting Compute Normal to False for all boundaries, excepted at the bedrock where: (TODO : VERIFY THIS CONDITION)

ComputeNormal Condition = Variable GroundedMask
    Real MATC "tx + 0.5"

• 3/ Compute the nodal force induced by the water pressure at the base of the ice-shelf using GetHydrostaticLoads (executed only on the bedrock bc).
• 4/ Execute the Stokes solver. The contact is tested and updated during the non-linear iteration loop from the USF_Contact user function in the bedrock bc:

Slip Coefficient 2 = Variable Coordinate 1
    Real Procedure "./USF_Contact" "SlidCoef_Contact"

• 5/ Solve for the upper free surface evolution using the FreeSurfaceSolver (See information here, and you will also need the USF_Zs user function).
• 6/

Favier L., O. Gagliardini, G. Durand and T. Zwinger, 2012. A three-dimensional full Stokes model of the grounding line dynamics: effect of a pinning point beneath the ice shelf. The Cryosphere, 6, 101-112, doi:10.5194/tc-6-101-2012.

Durand G., O. Gagliardini, B. de Fleurian, T. Zwinger and E. Le Meur. 2009. Marine Ice-Sheet Dynamics: Hysteresis and Neutral Equilibrium, J. of Geophys. Res., Earth Surface, 114, F03009, doi:10.1029/2008JF001170. [pdf]

Durand G., O. Gagliardini, T. Zwinger, E. Le Meur and R.C.A. Hindmarsh, 2009. Full-Stokes modeling of marine ice-sheets: influence of the grid size., Annals of Glaciology, 50(52), p. 109-114.