Deformation within polar ice sheets: An analysis of the Byrd Station and Camp Century borehole-tilting measurements

Abstract

Analysis of the inclinometer surveys of the boreholes at Byrd Station, Antarctica, and Camp Century, Greenland, yields the following results. The measured strain rates at both stations, in ice deposited in the last (Wisconsin) glaciation, reduced to a standard temperature and shear stress, are only about one-third those in the Holocene ice, even though the Wisconsin ice has a strong single-maximum fabric. Variations in strain rate in the Wisconsin ice at Byrd Station are negatively correlated with the number of volcanic dust bands in the ice. It is inferred that the ice below 1800 m at Byrd Station, which has a multiple-maximum fabric, deforms much less readily than the remainder of the ice. A flow model of Nye, with index n = 3, provides a relation between shear strain rate and shear stress that fits the data from both stations satisfactorily, even though the assumption of plane strain is not strictly valid at Byrd Station. A value of flow parameter A fifteen to twenty times that given by recent data compilations and predicted by dislocation theory, has to be used for the Holocene ice. These data cover a stress range (20–45 kPa) lower than in any other field experiment.