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Current Research
I am part of a team that writes computer models to explain how ice flows in the Greenland Ice Sheet. Our study area is just north of Jakobshavn Isbrae in Western Greenland. Although people tend to think of glaciers as very hard and solid objects, they actually behave as a fluid and flow like a very viscous river. In our models, we try to incorporate as many of the physical processes that influence ice flow as possible, from the slow viscous flow driven by gravity, to the effect of ice temperature on ice viscosity. We travel to Greenland to collect field data which is used to both calibrate and validate our models. For example, in situ meteorological observations are used to model surface mass balance (i.e. ablation and/or accumulation), while modeled ice velocities are compared against in situ GPS velocity measurements. Given the inaccessibility and vastness of our study area (~ 10,000 km2), remotely sensed datasets are very important. Remotely sensed datasets of ice surface elevation (by laser altimetry) and ice thickness (by ice penetrating radar) are used to model the ice dynamics (i.e. flow due to deformation) within the study area. Remotely sensed data is also useful in calibrating our ice flow models, as modeled ice flow velocities can be compared to those inferred by satellite.
Recently, basal sliding speed (the speed at which ice slides over the bedrock) has been observed to vary on relatively rapid time-scales (i.e. daily) within our study area. This has been attributed to pulses of surface meltwater reaching the ice-bed interface via moulins (vertical water conduits within the ice sheet). Due to climate change, warming air temperatures are expected to result in increased melt and runoff from the Greenland Ice Sheet over the next century. This increased melt is expected to make the ice-bedrock interface more slippery than it is today, and allow the ice sheet to flow into the ocean faster than it does today. One of the main uncertainties our modeling group hopes to assess is how the magnitude and/or spatial distribution of basal slide may evolve over the next century within our study area. We hypothesize that the magnitude and distribution of basal slide is closely related to the magnitude and distribution of moulins. To address this question, we are using commercially acquired WorldView-1 visible band imagery (~ 50 cm resolution) to quantify the spatial distribution of moulins within our study site.
It is necessary to understand how the ice flows in the Greenland Ice Sheet today in order to predict how the ice will flow in the future. It is important for society to know how much faster the Greenland Ice Sheet will flow in the future, because increased ice flow will result in increased iceberg calving and the raising of sea level. It is likely that the melting and increased iceberg calving of the Greenland Ice Sheet will contribute between 20 and 100 cm of sea level rise over the next 90 years.
Supervisory Committee
Illustrative Figures
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Ice surface topography within our studay area obtained from Advanced Very High Resolution Radiometer (AVHRR) satellite images (Scambos and Haran, 2002). The Dead Glacier flowline (black line) and in situ GPS / meteorology stations (stars) are also shown. |
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Log10 Ice surface velocity within our study area obtained from interferometric synthetic aperture radar (InSAR) satellite images (Rignot and Kanagaratnam, 2006). The Dead Glacier flowline (black line) and in situ GPS / meteorology stations (stars) are also shown.
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Modeled velocity cross-section along the flowline between the main elevation divide of the ice sheet and the terminus of Dead Glacier during the fall season. Cross-section surface and bed elevations are shown in black.
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Modeled velocity along the flowline between the main elevation divide of the ice sheet and the terminus of Dead Glacier over a 15 year period. The annual basal slide cycle is evident in the terminal 75 km of the flowline.
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Panchromatic WorldView-1 2009 imagery of a supraglacial lake near Swiss Camp, Greenland. The 1985 outline of the lake, georeferenced from a topographical map, has been overlaid in blue.
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Panchromatic WorldView-1 2009 imagery of a moulin and supraglacial river system just north of Jakobshavn Isbrae.
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