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Grad student talk - Contributions of sub-debris melt and ice face retreat to the rapid deflation...

Thursday, October 27, 2011, 4:30AM - 5:30AM


Leif Anderson



RL-1 269

Full title of talk: "Contributions of sub-debris melt and ice face retreat to the rapid deflation of the debris-covered Kennicott Glacier Terminus, Wrangell Mountains, Alaska."

Debris covered glaciers are common in tectonically active or highly erodible ranges such as the Himalaya, Tien Shan, Alps, Southern Alps, and the Wrangell Mountains. Debris cover has a variable effect on the mass balance profile depending on its thermal conductivity, albedo, and thickness. Although debris cover generally reduces melt, melt within debris covered zones is complicated by the presence of bare ice faces which retreat at high rates relative to melt beneath debris. As the need to extrapolate individual glacier mass balance into regional trends grows under a changing climate and rising sea level, it is imperative that we develop a full understanding of the factors that alter glacier mass balance, in this case: debris-cover and ice face retreat.

In order to understand the influence of debris-cover on the retreat and deflation of glaciers, we completed a field campaign on the 43km long Kennicott Glacier in south-central Alaska from June to mid-August 2011. This valley glacier supports a 26kmsup2/sup debris-covered terminus with a high concentration of exposed ice faces relative to other debris covered glaciers. The debris covered zone exhibits extensive thermokarst and the distribution of ice cliffs is influenced by the presence of large sinuous supraglacial streams. Previous laser altimetry research on Kennicott glacier reveals that surface elevations have decreased in the debris-covered terminus at a rate of 0.34m/yr (1957-2000), and Precipitation-Temperature Area Altitude modeling shows monotonic ice loss from 1957-2008. Rapid deflation in the debris-covered terminus is likely the result of reduced ice advection from up glacier or increased melt in the debris-covered portion of the glacier over the last half century.

As a first step to understanding this rapid surface elevation reduction, we document melt beneath debris of variable thickness at 60 locations using ablation stakes, the horizontal retreat of 62 ice faces, and debris depth and surface temperature at 200 sites in the debris covered zone. We collected air temperature at three locations and temperature profiles through the debris at eight locations. We will document the orientation and concentration of ice faces using IKONOS imagery and then use a positive degree melt method with these temperature measurements to determine the contributions of melt beneath debris and ice face retreat to the total melt at the terminus.

Debris surface temperature data will be used to validate 30m resolution Landsat infrared data for the Kennicott Glacier and provide a necessary check on the infrared imagery often used in debris-covered glacier research. Thermal conductivity, derived from our profiles of temperature through the debris, in conjunction with our debris thickness data will be used to model the melt produced under the debris covered terminus of the glacier and be compared to our empirical results.

In further research, we will employ the feature tracking method to reveal spatial and temporal changes in advection and its effect on the elevation and extent of the debris-covered terminus of the Kennicott Glacier.