Glacier Recession and Ecological Implications at Glacier National Park, Montana
Carl H. Key, Starr Johnson, and Daniel B. Fagre, USGS/Biological Resources Division
Richard K. Menicke, National Park Service
Glacier National Park contains 37 named glaciers that currently exist in various cirque, niche, ice apron, group and remnant forms. Thorough glacier surveys began with mapping the first USGS 30-minute quadrangles (1904-1914), and the work of Alden (1914). Only two glaciers, Sperry and Grinnell, have repeated assessment of surface profiles and movement to potentially reconstruct a history of mass balance (Johnson 1980). An additional nine glaciers have been mapped for terminus positions at varying intervals, extending back to the mid-1800's (Carrara and McGimsey 1981, 1988). Evidence for a general, regional recession is not new, but was recognized early this century (Dyson 1940). What is now known as the Little Ice Age (LIA) culminated here during the mid-19th century when Park glaciers were at their late-Neoglacial maxima (Carrara 1989). Since then, retreat has been consistent, with previous studies referencing conditions up to the late 1970's.
After nearly a 20-yr hiatus, we have begun to update the state of knowledge about glaciers of the region. Efforts to assemble and digitize historic maps and monitoring information proceed, adding new data to broaden spatial and temporal coverage. Work to digitize and assess 11 previously-mapped glaciers is complete, including delineation of 1993 perimeters on six of those. Recently digitized USGS 7.5-minute quadrangles exhibit about 83 ice and snow bodies larger than 10 ha (24.7 ac), at the time of aerial photography (1963-1966). This, the only comprehensive Park survey of perennial ice and snow to date, includes the named glaciers, separate pieces of former glaciers, and assorted patches (ice aprons, glacierets and snowfields) which may have not been true glaciers even during the LIA. The actual number of true glaciers (past and present), and the total extent of glacial recession since the LIA has yet to be determined empirically.
On six glaciers mapped from 1993 aerial photos, and two mapped through 1979, retreat from 1850 termini ranged from 818-1440 m and averaged 1244 m. Overall retreat rates varied between 6-17 m/yr. Those glaciers were reduced in area by 62-80%, for an average shrinkage to 27% of the estimated area in 1850. Retreat rates were not constant over time on any single glacier, but roughly correlated with warm-dry trends in climate. Agassiz and Jackson Glaciers, for example, lost between 3-117 m/yr through various periods from 1850-1979 (Carrara and McGimsey 1981). Pulses of recession occurred during the 1920's through the mid-1940's, and seem to be recurring now, as evidenced by change since 1979.
Of interest to ecosystem modeling and climate change research is how observed glacier changes might affect streams and surface characteristics across a mountain landscape. Using calculated retreat rates and the park-wide status of perennial ice and snow in 1966, regional conditions were projected for 1850 and 1993 on a drainage to drainage basis. Total area occupied by ice at the end of the LIA was estimated to be 99 km2. Of 84 basins completely within the Park, 25 contained 1% or more perennial ice cover, and 19 contained 3% or more. Estimated quantities were reduced by 1993 to 26 km2 total ice cover, 18 basins at 1% or more perennial ice, and only 4 basins with 3% or more. Decreased perennial ice within glacial basins, coupled with reduced number of glacial basins overall, likely reduced the moderating influence of glaciers on stream flow regimes throughout the year, and amplified biotically-stressful declines in run-off, particularly in late summer. On an ecosystem basis, such changes potentially represented significant alterations to lake and stream hydrology, and ultimately aquatic biota, in just the last 150 years.
Further work in the Glacier Park area is needed to complete regional assessment of glacial recession, and address climatological and ecological implications. Efforts continue to map the LIA maxima and the present status of glaciers throughout the park, and to build digital spatial models of recession. We hope to acquire new aerial photography in 1998. From guidelines for a comprehensive monitoring program (Fountain et al. 1997), a need exists for first-time, repeated mapping of accumulation and ablation zones to derive, if possible, time series of equilibrium line altitude and mass balance. Other primary field measurements are needed for monitoring at least one benchmark glacier. Also, stream gauging is needed to more precisely measure glacier contribution to hydrologic processes, which link in various ways to biological responses. Finally, future plans include development of new analytical approaches using satellite technologies to map margins and surface characteristics of small alpine glaciers.
Alden, W.C., 1914, Glaciers of Glacier National Park: National Park Service, U.S. Department of Interior, U.S. Government Printing Office, Washington, D. C., 44 p.
Carrara, P.E., 1989, Late Quaternary glacial and vegetative history of the Glacier National Park region, Montana: U.S. Geological Survey Bulletin 1902, 64 p.
Carrara, P.E., and McGimsey, R.G., 1981, The late neoglacial histories of the Agassiz and Jackson Glaciers, Glacier National Park, Montana: Arctic and Alpine Research, v. 13, p. 183-196.
_______ 1988, Map showing distribution of moraines and extent of glaciers from the mid-19th century to 1979 in the Mount Jackson area, Glacier National Park, Montana: U.S. Geological Survey Miscellaneous Investigations Map I-1508-C, scale 1:24,000.
Dyson, J.L., 1940, Recession of glaciers in Glacier National Park, Montana: American Geophysical Union Transactions, 21st Annual Meeting, pt. 1, p. 508-510.
Fountain, A.G., Krimmel, R.M., and Trabant, D.C., 1997, A strategy for monitoring glaciers: U.S. Geological Survey Circular 1132, 19 p.
Johnson, Arthur, 1980, Grinnell and Sperry Glaciers, Glacier National Park, Montana - A record of vanishing ice: U.S. Geological Survey Professional Paper 1180, 29 p.
Following the Glacier Monitoring Workshop, Vice President Al Gore, having seen some of our figures in climate change documents, expressed a personal interest in learning more about the glacier research being conducted at Glacier National Park. On 9/2/97 the Vice President visited for a hike to Grinnell Glacier, accompanied by Montana Senator Max Baucus, former Congressman Pat Williams and the authors. Grinnell Glacier provided a dramatic setting in which to discuss climate change issues and the value of glacier investigations.