SURFACE MEASUREMENTS OF RETAINED WATER EQUIVALENCE ON THE TAKU GLACIER, JUNEAU ICEFIELD, AK

As the largest, maritime, temperate glacier fed by the Juneau Icefield, the Taku Glacier has been the subject of mass balance studies for decades. Past measurements have typically yielded positive overall volume gains, which is consistent with a general regime of advancement. Since 1890, the termini of the Taku, and the Hole-in-the-Wall Glacier fed from the Taku trunk, have advanced 7 km and 3.2 km, respectively. During July/August, 2001, nine test pits, extending from 4.7-8.0 m in depth, were dug above the ELA through a range of elevations from 940-1760 m on the main Taku trunk and several tributaries. Each pit was sampled for density through a vertical column of 2000-2001 snow/ice, and the presence of ice structures was noted. Field data were grouped according to pit elevation. Through this method five elevation ranges were established, each encompassing 250 m increments from 750-2000 m of elevation. Ablation occurring after field data were obtained, and prior to the seasons first snowfall, is not factored into the following calculations. The lowest elevation range, 750-1000 m, had a retained water equivalent of 99.60 m³. Subsequent ranges, 1000-1250 m, 1250-1500 m, 1500-1750 m, and 1750-2000 m had values of 505.18 m³, 1434.66 m³, 569.78 m³, and 212.99 m³, respectively. Surface measurements show that 2822.22 m³ of water equivalence was retained over an area of 712 km² above the ELA, thus contributing to the long-term positive budget. The termini of the Taku and the Hole-in-the-Wall Glaciers continue to advance, while adjacent glaciers retreat, is probably the result of such a large accumulation area above the ELA.