Ice-thickness measurements of Taku Glacier, Alaska, U.S.A., and their relevance to its recent behavior

Abstract

Using radio-echo soundings and seismic reflections, we measured cross-sections of Taku Glacier, near Juneau, Alaska, to resolve inconsistencies in previous measurements and to understand better the glacier’s dynamics. The maximum thickness is about 1477 m and the minimum bed elevation is about 600 m below sea level, which establishes Taku Glacier as the thickest and deepest temperate glacier yet measured. Our data indicate that, during the 19th century, the terminus of Taku Glacier may have begun its rapid advance at a position where the ice bed was greater than 300 m below sea level and more than 25 km from the inland end of its submarine trough; this behavior is uncharacteristic of temperate tide-water glaciers. The glacier, which no longer calves, has eroded a sediment layer 100 m thick since 1890 at an average rate of about 3 m a−1 since 1948; this high erosion rate retards advance by entrenching the glacier into the terminal moraine. Calculations based on ice-deformation theory indicate significant basal ice motion near the terminus and high basal shear stress (140–220kPa) along much of its length. Estimated differences between ice flux and balance flux are consistent with observed thickening and positive net mass balance; these data indicate that ice volume is increasing and that further advance is likely.

The equilibrium flow and mass balance of the Taku Glacier, Alaska 1950–2006

“…The centerline depth of the glacier is greater than 1400 m at Profile IV (Fig. 9) The results on Profile IV match closely the results of Nolan et al (1995), with a maximum depth of 1450 m in this study versus 1400 m, certainly equivalent within the error limits.…”

“…Taku Glacier, however, has exceptionally thick ice, and a low basal gradient. The flow law for internal deformation suggests that negligible basal sliding is taking place in the accumulation zone (Nolan et al, 1995). The lack of seasonal velocity changes noted in this study and the remarkable uniformity in velocity suggest that sliding is a minor part of the glacier velocity at Profile IV.…”

“…The greatest thickness of the Taku Glacier was noted to be 1477 m at Goat Ridge, 22 km above the terminus (Nolan et al, 1995). The centerline depth of the glacier is greater than 1400 m at Profile IV (Fig.…”

“…Seismic methods are required to determine ice depths on transverse profiles because of the thickness of the Taku Glacier (Nolan et al, 1995). The seismic program completed measurements of ice thickness along eight transects across the glacier, each following the same transects and using the same points used in the GPS movement and elevation surveys.…”

“…Taku Glacier is also noteworthy for its positive mass balance from 1946-1988(Pelto and Miller, 1990, during a period when alpine glacier mass balances have been dominantly negative (Dyugerov and Meier, 1997). Finally, it is unique as the thickest alpine glacier yet measured, with a fjord extending 38-48 km upglacier from its terminus (Nolan et al, 1995).…”