McCall Glacier is located in the northeast Brooks Range of Arctic Alaska. This glacier was studied during the IGY in 1957 and in the early 1970s. During 1993 and 1994 we returned to the glacier in order to investigate how it has changed over the last 36 years. The ice surface and the outline of the terminus were surveyed using optical and GPS methods, and ice thickness was determined by radio echo sounding methods. Continuous measurements of temperature, precipitation, short-wave radiation and snow depth have been made since June 1993. In addition, the surface elevation and terminus of five other glaciers of different size and aspect within 20 km of McCall Glacier were also surveyed.

A contour map of the bed of McCall Glacier was made from the ice depth measurements. The present velocity field, the elevation and volume change from 1972 to 1993, and the average mass balance during this period were determined from the surveys. Annual velocities 1993/94 were similar to those measured in the 1970s. However, in the ablation area, 1993 summer velocities were about 30% higher than the annual velocities there, indicating that McCall Glacier slides in summer. This may imply that McCall Glacier is not a 'cold' glacier in the strict sense. Surveys show that the glacier surface has dropped everywhere - from a few m high in the accumulation zone to more than 40 m near the terminus. A map of this elevation change (Figure 1) shows that the total volume change was -5.5x107 m3 of ice, and that the long term mass balance was -0.33 ma-1. These results indicate that McCall Glacier is not healthy, especially considering its low mass exchange rate (typical winter balance is only 0.2ma-1). From 1958 to 1971 a mass balance of -0.13 ma-1 was found in an earlier study; indicating that the mass wastage has increased. Repeated surveys of detailed profiles across the lower ablation area from 1969 to 1994 show that a threefold increase in the rate of surface lowering occurred after 1975. Studies are under way to relate these negative mass balances to changes in the climate of the Arctic.

NSF Grant DPP 92-14954: Scientific personnel; B. Rabus, K. A. Echelmeyer, C. S. Benson and D. Trabant (USGS).