Study Area

Eliot Glacier is a small alpine glacier (~1.6 km2) located on the northeast side of Mount Hood, Oregon (Figure 1). The glacier descends from a steep headwall of geothermally altered rock, which is mechanically weak and prone to occasional rock avalanches (Lundstrom, 1992). In addition, the adjacent Cooper Spur is composed of block and ash flows and provides another debris source to the eastern portion of the glacier (Crandell, 1980). As a result, the lower portion of Eliot Glacier and much of the ablation zone, ~27% of the total area, is covered with rock debris. The debris thickens with decreasing elevation; “clean” ice at 2120 m and over 1.5 m thick debris at the terminus (Lundstrom, 1992). The debris cover reduces ablation significantly and is an important factor in glacier mass balance (Conway and Rasmussen, 2000; Kayastha and others, 2000). Debris is only found on two other Mount Hood glaciers: Coe (23% of the total area) and Ladd (41%).

Figure 1

Figure 1. Map of Eliot Glacier showing measurement locations and elevation profiles.

The Eliot Glacier was first photographed in 1901 (Reid, 1905) and these four photographs were used as a baseline for studies in the 1920s and 1930s (Marshall and others, 1925; Phillips, 1938). Detailed measurements of melt, surface elevation, and velocities began in 1940. Elevation measurements along two transverse profiles (A and B) showed the glacier thinned from 1940-1956 (Dodge, 1964). Dodge (1964) described an “ice wave” in 1958, which is a kinematic wave (Meier, 1962), and was a response to the positive mass balance (Dodge, 1971). From 1956 to 1982, when the upper profile was last surveyed, the glacier thickened by 50 m (Dodge, 1987). Surface velocities along the centerline decreased from 3.5 m yr-1 at the (B) profile (Figure 1) in the early 1940s to 1.4 m yr-1 prior to the wave, then accelerated to 6.9 m yr-1 in the late 1950s and the 1980s (Matthes and Phillips, 1943; Dodge, 1964; Lundstrom, 1992). Eliot Glacier retreated from 1901 to 1959, when the last measurements of terminus location were made. We remeasured the terminus location and measured the debris thickness, ice ablation rate, and glacier velocity for comparison against Lundstrom's (1992) measurements in the 1980s.