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Victoria University Antarctic Research Expedition Science and Logistics Reports 2003-04: VUWAE 48

Victoria Lower Glacier

Victoria Lower Glacier

Fig.2 Mass balance measurement device at Victoria Lower Glacier

Fig.2 Mass balance measurement device at Victoria Lower Glacier

During the 1999/2000 season three submergence velocity devices [Hamilton and Whillans, 2000] for mass balance measurements in the McMurdo Dry Valleys were installed (Fig.2). This method is used to determine mass balance by comparing vertical velocity of a marker in firn or ice with long-term, average snow accumulation rates. The movement of the marker is the result of three motions: firn compaction, gravitational glacial flow, and changes in mass balance. The device (Fig.2) consists of a non-stretchable, stainless steel wire attached to a metal anchor that is heated and placed into a drilling hole drilled in firn (or ice). The anchor melts the bottom ice and freezes in. A wire is stretched tight and guided by a stainless steel tube from the top of the drilling hole. A rod is held in place using plywood that has been buried ∼40cm into the snow to avoid melt around the darker wood surface. The top end of the wire has a loop and permanent marker, the tracking point. High precision GPS measurements are used to determine absolute position of the tracking point during subsequent years. Density measurements are made on the core recovered from the drilling. To calculate the surface slope in the direction of the glacier flow, the ice surface topography is surveyed using GPS in the vicinity the device. We revisited the three sites to measure current mass balance in continuation of the time series over the last 4 years. A GPS base station was deployed for the time of our visit at Staeffler Ridge. Our time series indicates a negative mass balance of about 12cm per year.