The goal of each summer season is to take measurements in early spring (Oct/Nov) and late summer (late January). This provides a measure of seasonal winter/summer changes of glacier mass.
The methods of data collection are described in the glacier stake heights, snow depths and glacier snow density metadata files. To convert the data to mass values, the total change in ice height (usually negative) and snow height (depth for snow covered ice) at each stake are multiplied by their respective densities. The density for ice is 0.9 g/cm3 and the density for snow is measured in nearby snowpits. The final error of the mass balance measurement is based on the errors in the stake heights and snow depths found by replicated measurements. The errors were carried through the calculations based on Baird, D.C., 1962. Experimentation: An Introduction to Measurement Theory and Experiment Design. Prentice Hall, Englewood. We assume no error in the snow density measurements. A Note about Stake names A stake with an H or V indicates a stake along the ice cliff that forms the boundary of the glacier terminus. An H is a horizontal stake placed into the vertical wall of the glacier terminus, and V is a stake placed into the ice apron at the base of the ice cliff. The vertical stakes were installed to support the horizontal stakes and provide a nearby measure of ablation for a surface with a much different slope. A Note about the Zone variable: The accumulation zone is the region on the glacier where snow accumulation exceeds ablation, therefore the region is always snow covered, and typically restricted to the higher altitudes of the glacier. The ablation zone is the region where ablation exceeds snow accumulation and the surface is ice, although occasionally covered with seasonal snow. This is important for evaluating the other variables. In the accumulation zone, for example, there will be no height to ice. A Note about Ice WEQ Change: The density used can be calculated from snow height change, or directly examined in the glacier snow density file. A Note about Standard Deviation Calculations: During the early years only one or two measurements of surface height were taken at each stake. If two measurements were taken, the average was used and the range expressed as the error; note of this was made in "comments" field. If greater than 2 measurements of surface height and snow depth were taken, standard deviation of Total WEQ Change was based on a calculation of errors.