Deformation, strength and tectonic evolution of basal ice in Taylor
Glacier, Antarctica
Abstract
Observation and measurements of ice structure and deformation made in
tunnels excavated into the margin of Taylor Glacier reveal a complex,
rapidly deforming basal ice sequence. Displacement measurements in the
basal ice, which is at a temperature of -18°C, together with the
occurrence of cavities and slickenslides, suggests that sliding occurs
at structural discontinuities within the basal zone although we cannot
rule out the possibility of rapid deformation in thin zones of high
shear. Strain measurements show that the highest strain rates occur in
ice with average debris concentrations of 26% followed by ice with
debris concentrations of around 12%. The lowest strain rates occur in
clean ice that has very low debris concentrations (<0.02%).
Deformation within the basal ice sequence is dominated by simple shear
but disrupted by folding which results in shortening of the
debris-bearing ice followed by attenuation of the folds due to
progressive simple shear which generates predominantly laminar basal ice
structures. About 60% of glacier surface velocity can be attributed to
deformation within the 4.5 m thick sequence of basal ice that was
monitored for this study, and 15% of motion can be attributed to
sliding. The combination of high debris concentrations and high strain
rates in the debris-bearing ice means that material transported in the
basal ice is exposed to a high rates of abrasion which produces heavily
striated and facetted clasts typical of temperate glaciers even though
the basal ice is at a temperature of -18°C.