This project has three parts: glacier facies, analysis of accumulation on the Greenland Ice Sheet, and snow pit and core data from the summit caldera of Mt. Wrangell, Alaska.

Glacier Facies

Glaciers, especially large ones such as the Greenland and Antarctic ice sheets, span several environments which give rise to different physical characteristics in the upper layers of snow and firn. A scheme of glacier facies was established in 1960 to define the differences in terms of physical measurements that penetrate several annual stratigraphic units of accumulation. The original definition of glacier facies was based on research in Greenland, and it included the full range of glacier facies. Some parts of the Antarctic ice sheet have only the upper end of the glacier facies spectrum, and many glaciers have only the lower end of the spectrum. For example, McCall Glacier in the Brooks Range of arctic Alaska does not extend to the upper limit of the wet snow facies. Modifications to the original definitions have been in the lower end of the spectrum, where complications due to melting are greatest.

One goal of this project is to determine the extent to which glacier facies can be identified from satellite imagery. The facies boundaries we can expect to define on Landsat images are restricted to those that are visible at the surface. The potential of SAR imagery to see below the surface was discussed at the 4th Workshop on Mass Balance and Related Topics (see references) and Fahnestock and others have now shown that the dry-snow and wet-snow lines may be mapped by SAR imagery (Science, Vol. 262, p. 1530-1534, 1993).

Analysis of accumulation on the Greenland Ice Sheet

We are redrawing a contour map of annual accumulation for the ice sheet by using the existing glaciological pit and core data from Greenland, combined with data from coastal meteorological stations, and a model for orographic precipitation.

Snow pit and core data from the summit caldera of Mt. Wrangell, Alaska

Snow stratigraphy from the years 1950-1982 are being analyzed by using pit and core data which includes detailed density determinations together with microparticle analysis and data on the stable isotopes of Hydrogen and Oxygen. The interpretation is made easier because the summit region lies in the dry-snow facies, so it experiences negligible melt.

NSF Grant DPP 90-02345: Scientific personnel—; C. S. Benson.