UBC Theses and Dissertations
Inverse modelling of subglacial hydraulic processes Racz, Gabriela Clara
Numerous studies have documented that water at the ice-bed interface can affect the ice flow dynamics of both mountain glaciers and ice sheets. Water at the bed is routed through a complex network of conduits that form a subglacial drainage system, which evolves over the melt season in response to the changes in the meltwater supply. Despite its significance, our understanding of the subglacial hydraulic processes remains limited due to the inaccessibility of the glacier bed. This thesis aims to address this knowledge gap by using a dense record of basal pressure time series from a mountain glacier in the St. Elias Mountains, Yukon Territory called South Glacier and answering: (i) what insights can we gain by using inverse modelling to reconstruct the seasonal evolution of the subglacial drainage system, and (ii) whether we can identify and improve our understanding of physical processes that are driving abrupt changes in the behaviour of a pair of basal pressure time series, that we refer to as `switching events'. We developed an inverse model for estimating the permeability of the subglacial drainage and its changes over the melt season. Our results indicate that the inverse model can effectively reconstruct the permeability field and its seasonal changes, and, therefore, provide valuable information about the evolution of the subglacial drainage system under the South Glacier. More importantly, this method can be applied to other glaciers with sufficiently dense borehole data. It is worth pointing out, that a thorough sensitivity study on synthetic data highlighted the importance of considering factors such as heterogeneous englacial water storage, offsets in hydraulic potential measurements, and the delays in the estimates of meltwater supply to the glacier bed when interpreting the inversion results. In the second part of this thesis, we thoroughly examined two potential mechanisms that could be driving switching events, and found that they were unable to explain the behaviour in observed data. However, the created catalogue of switching events has proven to be a valuable resource in evaluating the validity of hypotheses related to the underlying physical processes behind the switching events.
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