Glacier Change on the Three Sisters Volcanoes, Oregon: 1900--2010

A glacier responds to changes in climate by subsequent retreat and advance as a result of changes in snow inputs and outputs. Understanding these changes is important because shrinking glaciers limit and diminish local water resources. They contribute to alpine runoff in the late-summer months by delaying the maximum runoff until late in the melt season. A comprehensive glacier and perennial snowfield inventory has not been completed for the Three Sisters in Central Oregon. Using aerial photography, Digital Elevation Models (DEMs), previous studies, and historical ground based photographs these glacier and perennial snowfields were defined and their surface area change was quantified along with surface area and volume change for the 15 named glaciers for multiple years. The glaciers and perennial snowfields totaled 9.03 +/- 1.65 km 2 in 1949 and decreased to 7.1 +/- 1.16 km2 in 2003 giving a total loss of -1.914 +/- 0.974 km2 (-21%). The 15 named glaciers totaled 12.43 +/- 0.417 km 2 in ∼1900 and decreased to 5.65 +/- 0.135 km2 in 2003 giving a total loss of -6.70 +/- 0.439 km2 (54%) with more loss occurring in the early part of the century. It's estimated that the 15 named glaciers lost roughly 61% of volume from 1900 to 2010. From 1957 to 2010 their surface's dropped in elevation on average by -8.9m, losing an estimated 71.96 x 106 +/- 2.87 x 106 m3 (53%) in total volume, seen across accumulation and ablation zones, with more loss happening from 1957 to 1990. There was no relationship found between topography and area. A small correlation was found between slope and increased volume change. Debris cover on glacier surfaces has increased and showed a correlation between decreasing area loss (no correlation with volume changes).