Terminus Advance, Kinematics and Mass Redistribution During Eight Surges of Donjek Glacier, St. Elias Range, Canada, 1935 to 2016

Donjek Glacier has an unusually short and regular surge cycle, with eight surges identified since 1935 from aerial photographs and satellite imagery with a ∼12 year repeat interval and ∼2 year active phase. Recent surges occurred during a period of long-term negative mass balance and cumulative terminus retreat of 2.5 km since 1874. In contrast to previous work, we find that the constriction where the valley narrows and bedrock lithology changes, 21 km from the terminus, represents the upper limit of surging, with negligible surface speed or elevation change up-glacier from this location. This positions the entire surge-type portion of the glacier in the ablation zone. The constriction geometry does not act as the dynamic balance line, which we consistently find at 8 km from the glacier terminus. During the 2012–2014 surge event, the average lowering rate in the lowest 21 km of the glacier was 9.6 m a−1 , while during quiescence it was 1.0 m a−1 . Due to reservoir zone refilling, the ablation zone has a positive geodetic balance in years immediately following a surge event. An active surge phase can result in a strongly negative geodetic mass balance over the surge-type portion of the glacier