A CONTINUUM MIXTURE MODEL OF ICE STREAM THERMOMECHANICS IN THE LAURENTIDE ICE-SHEET .1. THEORY

We employ a continuum mixture framework to incorporate ice streams in a three-dimensional thermomechanical model of the Laurentide Ice Sheet . The ice mass is composed of a binary mixture of sheet ice, which def orms by viscous creep, and stream ice, which flows by sliding and/or s ediment deformation at the bed. Dynamic and thermal evolutions are sol ved for each component in the mixture, with coupling rules to govern t ransfer between flow regimes. We describe two different transfer mecha nisms: (1) creep exchange, the nourishment of ice streams by viscous c reep inflow from the surrounding ice sheet, and (2) bed exchange, the activation, growth, and deactivation of ice streams, perpetrated by tr ansfers of bed area between flow constituents. This paper develops the underlying mixture theory. We express the governing equations for mas s, momentum, and energy balance in a form suitable for direct incorpor ation in existing numerical models of ice thermomechanics. A companion paper in this issue explores mixture and ice stream behavior in appli cations with the Laurentide Ice Sheet.