Glacier dynamics in the Susitna River basin, Alaska, U.S.A.

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Abstract
The dynamics of the glaciers which form the headwaters of the Susitna River in central Alaska exhibit several interesting features, including a spectrum of surge-type behavior. A difference between balance flux and actual down-glacier transport, which is taken to be an indicator of surge behavior, shows West Fork Glacier and two tributaries of Susitna Glacier to be surge-type of varying strengths, while East Fork Glacier and one tributary of Susitna Glacier to be non-surge-type. The main trunk of Susitna Glacier and its two unstable tributaries surge simultaneously with a period estimated to be 50–60 years. Having last surged in 1951–52, its next surge should be expected sometime in the first decade of the next century. West Fork Glacier last surged in about 1935 and again in 1987–88, indicating a similar surge period of about 50 years. Significant seasonal velocity variations were observed during the glacier’s quiescent phases, with increases of 30–100% over background occurring early in the melt season. In some cases, the annual minimum occurred during late summer, implying that basal motion contributes measurably to winter velocity on at least some glaciers in the area. Events of rapid motion lasting a day or so also occur occasionally during the melt season and may account for brief velocity increases of up to 300%.