Date of Award
Doctor of Philosophy (PhD)
This thesis explains the annual ice velocity cycle of the Sermeq (Glacier) Avannarleq flowline, in West Greenland, using a longitudinally coupled 2D (vertical cross-section) ice flow model coupled to a 1D (depth-integrated) hydrology model via a novel basal sliding rule. Within a reasonable parameter space, the coupled model produces mean annual solutions of both the ice geometry and velocity that are validated by both in situ and remotely sensed observations. The modeled annual velocity cycle reproduces the broad features of the annual basal sliding cycle observed along this flowline, namely a summer speedup event followed by a fall slowdown. The summer speedup event corresponds to conditions of increasing hydraulic head during inefficient subglacial drainage, while the fall slowdown event corresponds to conditions of decreasing hydraulic head during efficient subglacial drainage. Calculated coupling stresses diminish to less than 10 % of total driving stress within 6 km upstream of the Sermeq Avannarleq terminus. This suggests that the annual ice velocity cycle observed at CU/ETH ("Swiss") Camp (46 km upstream) is unlikely to be the result of velocity perturbations being propagated upstream via longitudinal coupling, but instead reflects local surface meltwater induced ice acceleration. This thesis also compares high-resolution 1985 and 2009 imagery of the Sermeq Avannarleq ablation zone to assess changes in crevasse extent and supraglacial hydrology. The area occupied by crevasses > 2 m wide significantly increased (13 ± 4 %) over the 24-year period. This increase consists of an expansion of existing crevasse fields, and is accompanied by widespread changes in crevasse orientation (up to 45°). The increase in crevasse extent is likely due to a combination of ice sheet thinning and changes in flow direction, both stemming from the recent acceleration of nearby Jakobshavn Isbrae. A first-order demonstration that moulin-type drainage is more efficient than crevasse-type drainage in transferring meltwater fluctuations to the subglacial system suggests that this transition may dampen the basal sliding sensitivity of portions of the ice sheet that are not presently crevassed. An increase in crevasse extent may also enhance mass loss through increased surface ablation and increased deformational ice velocities due to facilitated cryo-hydrologic warming.
Colgan, William T., "Investigating the influence of surface meltwater on the ice dynamics of the Greenland Ice Sheet" (2011). Geography Graduate Theses & Dissertations. 19.