No abstract

No abstract

A kinematic model of pressure ridge formation is presented, in which the lateral and vertical motion of ice blocks is combined with a force balance and breaking stress calculation. A computer program encompassing several physical processes has been used to simulate ridge formation in ice with thicknesses from 20 cm to 2 meters. The resulting profiles are compared with measured profiles of other authors. A lower bound to the force required to form ridges is calculated from an energy balance and found to be of the order of the forces that may result from wind loading on the ice. When the ridge model proceeds through many steps, a limit cycle is established that provides a limiting height for ridges. This height depends on the thickness and strength of the ice. Limiting height calculations are made for ice sheets from 20 cm to 4 meters thick.

A mechanical model is developed to describe the rafting of ice sheets of equal thickness. Rafting is one of the important deformation mechanisms in thin ice. The model predicts the force required to initiate rafting. This force is an upper bound for the force in pack ice. The model is also used to calculate the bending stress developed by rafting. The stress increases in proportion to the square root of ice thickness. Thus for a given ice strength there is a maximum thickness of ice which can raft without fracturing. For typical young ice properties the calculated value of 17 cm is in good agreement with field observation.