Short-term (~daily) variations in glacier surface dynamics, induced by variations in subglacial water pressures, may critically affect glacier response to global warming, and the contribution of glacier runoff to global sea levels, by influencing the transfer of ice to lower altitudes where surface melting is increased. This may be especially significant at High Arctic glaciers, where recent climate models predict that global warming may be exacerbated relative to lower latitudes. Recent field studies have demonstrated that significant short-term velocity variations occur at High Arctic glaciers but it is not known whether these motion anomalies propagate spatially and/or temporally, nor whether they result from changes in the structure of the subglacial drainage system. This study reports on short-term variations in glacier surface motion during two melt-seasons (2000, 2001) across the lower ablation zone of John Evans Glacier, Ellesmere Island, Canada. Here, warm ice (hence subglacial drainage) exists only as a thin (~10 m) layer at the basal interface, and is not present at the margins and terminus. Horizontal and vertical velocities of 33 marker stakes distributed across the lower ablation zone were derived every two days between June and August 2000 and 2001. A simultaneous programme of dye-tracing experiments revealed a significant evolution in the structure of the subglacial drainage system occurred beneath the lower ablation zone each melt-season. The results reveal a 2-4 day 'spring event' of high horizontal and vertical velocities occurs over the lower ablation zone each melt-season 2-3 weeks after the onset of surface melting. This is induced by the sudden penetration of stored surface meltwaters through cold ice to a distributed subglacial drainage system via a crevasse field 5 km above the terminus, inducing high subglacial water pressures and rapid subglacial drainage evolution under the lower ablation zone. After the spring event, horizontal velocities fall (although typically remain higher than overwinter levels until the end of summer) and vertical velocities change sign. Further transient periods of high horizontal surface velocities are observed when high meltwater inputs resume after periods of cold weather, or when unusually high meltwater inputs exceed the capacity of the channelised subglacial drainage system.
|Translated title of the contribution||Short-term variations in glacier dynamics in the ablation zone of a High Arctic polythermal glacier: relation to seasonal changes in subglacial drainage system structure|
|Title of host publication||European Geophysical Society/American Geophysical Union/European Union of Geosciences Joint Assembly, Nice, France|
|Publication status||Published - 2003|