POST-SURGE FIELD MEASUREMENTS OF ABLATION AND RETREAT, EASTERN SECTOR, BERING GLACIER, ALASKA

Significant loss of surface ice mass from the eastern piedmont lobe of the Bering Glacier has been measured using several methods from 1998 to 2005. Direct measurements of thinning and retreat, complemented by annual aerial and ground photography along a 20 km ice front, were accomplished using conventional and newly designed techniques. Data from June 2005 are consistent with the previous seven years of observation. Conventional surveys of ice surface gradient extending 1 km upglacier from two ice front sites to elevations below 100 m indicate that the post-surge loss of ice mass remains near the 10 m/year values noted since 1998. A calibrated cable placed 9.8 m in a steam drilled hole in June 2005 at the apex of the piedmont lobe will yield annual ablation at approximately 400 m above MSL for 2005-2006. Surface downwasting measured by progressive exposure of meter long, white PVC pipe placed in auger holes 90 cm deep at 3 sites during June 2005 yielded results of 5.7, 8.0, and 8.5 cm/day. These are well within the previously observed range of 4.4 to 10.9 cm/day. The significance of variable factors tested in 2005 that might influence these rates are ice crystal texture, foliation scale and orientation, per cent of debris cover, weather conditions, slope inclination and aspect, and elevation. Annual retreat of the ice front on land in the Tsivat Basin southward to Arrowhead Island in Vitus Lake was measured using differential GPS surveys accurate to +/- 2m. The 2005 results were similar to previously measured rates of 50-75 m/year. Calving retreat in adjacent ice contact lakes varies significantly depending on water depth.