Centreline surface elevation longitudinal profiles have been completed for three different points in time from historic photographs (∼1900), US Geological Survey maps (1964 and 1985), and field measurements (annually between 1984 and the present) for three North Cascade glaciers. Comparison of thinning and terminus behaviour over this time period indicates substantial overall volume loss during this century for each glacier.
Mean thickness changes along the longitudinal profile of Easton Glacier are losses of 46 m (0·68 m year−1) of ice thickness between 1916 and 1984 and 13 m (0·72 m year−1) between 1984 and 2002. Its terminus has retreated a net distance of 2123 m. Lower Curtis Glacier lost an average of 45 m (0·60 m year−1) thickness from 1908 to 1984 and 6 m (0·33 m year−1) from 1984 to 2002, with a net terminus retreat of 522 m. On Columbia Glacier, ice thickness loss was 57 m (0·78 m year−1) from 1911 to 1984 and 8 m (0·44 m year−1) from 1984 to 2002. The net terminus retreat for Columbia was 640 m. Thickness changes are approximately equal in the accumulation zone of the Columbia and Lower Curtis Glacier during the 20th century and from 1984 to 2002. This suggests that there is no position to which the glacier can retreat and achieve equilibrium.
The changes on each glacier, which today average less than 75 m in thickness, represent the loss of 35–50% in their volume since the turn of the century, and 10–15% of this volume since 1984. Their ongoing thinning indicates that these three glaciers will continue to retreat in the foreseeable future, the Columbia Glacier likely disappearing. Long-term monitoring of these glaciers should continue in order to assess the impact on downstream flow, which is utilized for hydropower on Easton and Lower Curtis Glaciers and a salmon hatchery on Columbia Glacier. Copyright © 2004 John Wiley & Sons, Ltd.