Intra-annual and intra-seasonal flow dynamics of a High Arctic polythermal valley glacier

Measurements of surface dynamics on polythermal John Evans Glacier, Nunavut, Canada, over two winter periods and every 7-10 days throughout two melt seasons (June-July 2000, 2001) provide new insight into spatio-temporal patterns of High Arctic glacier dynamics. In the lower ablation zone, mean annual surface velocities are 10-21m a-1, but peak velocities up to 50% higher are attained during late June/early July. In the upper ablation zone and lower accumulation zone, mean annual surface velocities are typically 10-18 m a-1, and peak velocities up to 40% higher occur during late July. In the upper accumulation zone, mean annual surface velocities are 2-9 m a-1, and motion in mid- to late July exceeds this by up to 10%. Rapid drainage of ponded supraglacial water in the upper ablation zone to an initially distributed subglacial drainage system in mid-June may force excess surface motion in the warm-based lower glacier. The data indicate that the duration of the velocity response may be related to the rate of channelization of the basal drainage, and the velocity response may be transmitted up-glacier by longitudinal coupling. An increase in surface velocities in the middle glacier in late July occurs in conjunction with the opening of two further moulins in the accumulation zone.