GLACIER CHANGE ON MOUNT RAINIER IN THE CONTEXT OF OTHER VOLCANOES IN THE CASCADE RANGE OF THE PACIFIC NORTHWEST

Glaciers in the Rocky Mountain West, are concentrated on the stratovolcanoes of the Cascade Range, which extend from California to the Canadian border. The volcanoes are much higher than the surrounding terrain and provide cooler and typically snowy conditions favoring the growth of large glaciers. Indeed, the largest glaciers in each state intersecting the Cascade Range (California, Oregon, and Washington) are found on a volcano. Understanding these glaciers are important for estimating water flow in late summer when the seasonal snow has largely disappeared and for assessing hazard potential because they generate outburst floods that may trigger debris flows.

Mount Rainier is an iconic glacier-clad volcano with glaciers (some debris-covered) mantling all sides of the mountain and different from the surrounding alpine landscape where they face north to east. Despite Rainier’s high elevation (> 4300 m) its glaciers may be more sensitive than expected from typical alpine glaciers because they, like glaciers on all volcanoes, narrow with elevation rather than expand. Taken together, Mount Rainier provides a unique opportunity to examine the combined effects of elevation, aspect, and debris cover on glacier change. By comparing volcanoes in the region, we can clarify glacier activity unique to Mt. Rainier and common to all the volcanoes.

We examine the area and volume changes of glaciers on Mount Rainier relative to glaciers on Mt. Baker, WA; Glacier Peak, WA; Mt. Adams, WA; Mt Hood, OR; Three Sisters, OR; and Mt. Shasta, CA. These volcanoes span about 7.5^o in latitude and vary in maximum elevation from 3200 to more than 4300 m. Changes in glacier area are derived from historic USGS maps and aerial or satellite imagery over a time period of about 50 years. Preliminary results show that total area change on each volcano varied from -5% to -26% (Mt. Rainier, -8%). Volume change, over the same period, was based on elevation differences calculated from the same historic maps and recent aerial lidar surveys. Average specific volume change (volume change divided by glacier area) for each volcano varied from about -6 m (Rainier) to -20m. Total area change for all volcanoes is -25.6 ± 2.2 km² and total volume change is -1.84 ± 0.36 km³. Differences between volcanoes, aspects, and elevations will be discussed.