Advance of Hubbard Glacier and 1986 Outburst of Russell Fiord, Alaska, U.S.A.

Abstract

Hubbard Glacier, the largest tide-water glacier in North America, has advanced since it was first mapped in 1895 by moving a protective submarine moraine into the entrance of Russell Fiord. In May 1986, a weak surge of the Valerie tributary of Hubbard Glacier caused the glacier to block the fiord entrance, converting the body of water into a large glacier-dammed lake. This lake filled to a height of 25.5 m and stored 5.4 km3 of water before it burst out on 8 October 1986, producing a peak flow of 105 000 m3 s−1 averaged for 1 h. Hubbard Glacier is expected to continue advancing because its accumulation area ratio (AAR) is 0.95, which is unusually large. Such an advance would undoubtedly block Russell Fiord again. If this happens, it is predicted that the lake will fill to a height of 39 m over a period of 1.1–1.5 years and then overflow into the Situk River near Yakutat. This, in turn, would increase the average flow of that small stream from ils present rate of between 10 and 15 ms−1 to an estimated annual average discharge of 230 m s−1. Such an increase in flow would be expected to flood and erode forest lands, fish habitats, subsistence fishing camps, archaeological sites, and roads. At the same time, the increased water depth in Russell Fiord could be expected to increase the calving rate of Hubbard Glacier, potentially threatening the stability of its calving terminus.