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Sea Ice Ridging and Rafting Structures: Is the Microstructural Controlled Transition from Ductile to Brittle Behavior on Earth Also Seen on Mars?
Abstract
From the similarity of sea ice pressure ridge between Mars and Earth, we infer that they first started from a ductile material to a single phase while deforming, resulting in brittle behavior near the end of the ridging process.
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.
Rafting and pressure ridging are important processes in the deformation of sea ice that occur when two ice sheets are pushed together. In this study a two-dimensional computer model of the rafting and ridging process is used to simulate a situation in which two identical ice sheets are pushed together at constant speed. Each model ice sheet is composed of two thicknesses of ice. The ratio of the thicknesses is varied to obtain degrees of inhomogeneity. The accuracy of the simulations is assessed by comparison with a series of similar physical experiments performed in a refrigerated basin. Following this comparison, the computer model is used to perform an extensive series of simulations to explore the effect of the thickness and the thickness inhomogeneity of the model ice sheets on the likelihood of occurrence of ridging and rafting. During the simulations the energy consumption and forces are explicitly calculated. The energy consumed during the simulations is used to demonstrate the smooth transition between ridging and rafting that occurs when the homogeneity of the sheets is varied.