Velocity variability of Devon Ice Cap tidewater glaciers

  • Author / Creator
    Danielson, Bradley D
  • Tidewater outlet glaciers drain approximately 47% of the ~105,000 km^2 covered by ice caps in the Queen Elizabeth Islands of Nunavut, Canada, suggesting that iceberg discharge may be an important process in the mass balance of these ice caps. Seasonal and inter-annual velocity changes of tidewater glaciers may result in the misestimation of annual or multi-year iceberg calving fluxes, if these are estimated on the basis of short-term ice velocity measurements derived from repeat satellite imagery. The aim of this study is to observe and quantify the variability of tidewater glacier velocity at a range of time scales, and to examine the processes driving these variations, with a focus on the impact of temporal and spatial variations in the delivery of surface meltwater to the glacier bed. High-frequency ice surface velocity measurements were made at four tidewater outlet glaciers of the Devon Ice Cap. Observations over three summers on Belcher Glacier revealed an annually consistent pattern of ice velocities higher than the annual mean during the 50-60 day long melt season. During this fast-flow period, surface meltwater entered the glacier via moulins and the rapid drainage of supra-glacial melt ponds and water filled crevasses. Rapid drainage events coincided with short-duration ice velocity fluctuations. Inter-annual variations in the magnitude of the enhanced velocity in summer and the velocity variability during the fast-flow period were linked to factors which affect the rate and timing of meltwater delivery to the subglacial drainage system, such as variations in spring snowpack thickness and the degree of variability in late summer meltwater production. The effective contribution to the annual displacement resulting from enhanced velocities during the summer melt season was only ~5-8% at the glacier terminus, due to the relatively short duration of the fast-flow period. On the lower 5-8 km of the Belcher Glacier and North Croker Glacier, multi-year changes in annual mean velocity were observed that were not clearly linked to inter-annual variations in the amplitude and/or timing of the seasonal velocity cycle. Because of their flow mechanics, these glaciers may be poised to respond extremely sensitively to even minor long-term changes in driving stress. For such glaciers, it may be extremely difficult to identify any obvious external forcing for relatively large, long-term changes in velocity and rates of iceberg discharge. Overall, the results provide a demonstration of the seasonal bias that may be expected in different zones of the Devon Ice Cap if annual mean glacier velocities are estimated from velocity measurements made over periods less than a full annual cycle.

  • Subjects / Keywords
  • Graduation date
    Spring 2014
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.