Crystal Fabric Studies on Emmons Glacier Mount Rainier, Washington

Abstract

Optical orientations of 1,725 ice crystals were determined at eleven locations on the Emmons Glacier by means of a 6-inch universal stage mounted between crossed polaroid sheets. The crystals were 0.2–6 inches across and from three to forty were included in each 4½ × 6-inch thin-section. Down-valley glacier movements of 3.4–9.2 inches per day were recorded at four of the higher locations, and another three were in ice believed to be essentially stagnant. The optic axes at most locations, when plotted on a Schmidt equal-area projection, form consistent patterns featuring four strong maxima at the corners of diamond-shaped quadrangles. Concentrations as high as 26 per cent in 1 per cent of the area were recorded. The angular separation of opposite corners of the diamond-shaped quadrangles average 84° and 52°, respectively. The pattern in stagnant ice is the same and as strong as the pattern in moving ice. Poles to shear planes and clear ice bands in the glacier at the locations studied fall near the centers of the diamonds. If this pattern is controlled by gliding within the ice crystals, it suggests the possibility of glide planes in ice crystals other than the well-known basal glide plane.