The Creep of Ice, Geothermal Heat Flow, and Roosevelt Island, Antarctica

Measurements of ice velocity, thickness, and surface topography on the large ice rise known as Roosevelt Island are consistent with Glen’s flow law, , for values of τ between 5 × 10 4 N m –2 and 1.4 × 10 5 N m –2 , and there is no indication of a reduction in n at low stresses. If n = 3 there must be progressive softening of the ice towards the edge of the ice rise, and this probably represents the combined effects of warming and recrystallization leading to a fabric favoring shear. Assuming that near the centre of the ice rise, where the effects of recrystallization are probably negligible, the ice behaves in the same way as randomly-oriented polycrystalline ice, then the geothermal flux G in this area is approximately 0.06 W m –2 . In the absence of measurements of deep-ice temperatures, the distribution of G across the ice rise cannot be determined. However, the simplest interpretation of the movement data requires: (1) a linear increase in G from 0.05 W m –2 on the north-east side of Roosevelt Island to 0.07 W m –2 in the south-west, and (2) strain-rate enhancement, due to recrystallization, that increases outward from the centre of the ice rise to reach a maximum value of approximately two near the edges. The calculated values of G are larger than the world average, but this is consistent with the probably granitic core beneath Roosevelt Island. An increase in G of 0.02 W m –2 in a distance of 60 km would require an increase in granite thickness of about 5 km.