Proposal for a constitutive equation of temperate firn

From deformation measurements at a 20 m deep firn pit, a constitutive equation for temperate firn under natural stress has been derived. The analytical and numerical formulation passes over into Glen's flow law for ice at the transition of firm to ice. Basis of the analysis is the determination of the shear strain rate from the tilt rate of the pit axis, under consideration of the longitudinal and vertical strain rates, the compressibility of the firn, as well as the triaxial pit deformation.