Glaciers on the Glacier National Park (GNP) landscape have ecological value as a source of cold meltwater in the otherwise dry late summer months, and aesthetic value as the park’s namesake features. USGS scientists have studied these glaciers since the late 1800s, building a body of research that documents widespread glacier change over the past century. Ongoing USGS research pairs long-term data with modern techniques to advance understanding of glacier physical processes, alpine ecosystem impacts, and climate linkages. By providing objective scientific monitoring, analysis, and interpretation of glacier change, the USGS helps land managers make well-informed management decisions across the Glacier National Park landscape.
WHAT IS A GLACIER? Aglacieris a body of snow and ice that moves under its own weight. Glacier movement may be detected by the presence of crevasses, cracks that form in the ice as the glacier moves. All glaciers are dynamic, changing in response to temperature and precipitation – growing when winter snowfall exceeds summer melting, and shrinking when melting outpaces accumulation of new snow. Most of the glaciers in Glacier National Park are relatively small cirque glaciers, occupying alpine basins along the Continental Divide. In GNP, ice bodiesareclassified as glacierswhentheirareaexceeds0.1 km2(100,000 m2), or about 25 acres.
TRACKING GLACIERS OVER TIME: Theextensive valley glaciers that carved GNP’s majestic peakswere part of a glaciation that ended about 12,000 years ago. The smaller alpine glaciers that cling to mountainsides today have been present on the landscape since at least 6,500 years ago. These glaciers grew substantially during the Little Ice Age (LIA) that began around 1400 AD and reached their maximum size around 1850 AD. Their maximum sizes can be reconstructed from the mounds of rock and soil left behind, known as moraines.A comprehensive inventory of moraines visible in satellite imagery revealed that there were 80 glaciers (>0.1 km2) at the peak of the Little Ice Age in GNP’s boundary. Similarly, comprehensive analysis of modern glacier extent documented in satellite imagery showed that in 2005, the number of glaciers >0.1 km2 had decreased to 32. Thus, over the roughly 150 years between the mid-19th century LIA glacial maximum and the advent of the 21st century, the number of glaciers >0.1 km 2 within GNP decreased by nearly 60%.
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Comprehensive inventories of glaciers across the Glacier National Park landscape include named and unnamed glaciers. Yet inspecting the subset of named glaciers alone reveals the same trend of glacier loss. This time series of glacier retreat reveals glacier loss and area reduction since 1966.
All glaciers in Glacier National Park have decreased in area, but the rates of retreat are not uniform. Studies of local topographic effects show that variations in glacier geometry, ice thickness, elevation, shading, input from avalanching, and the contribution of wind-deposited snow, likely account for each glacier’s unique rate of change.
HOW MANY GLACIERS IN GNP?
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The USGS uses aerial photographs and satellite imagery to delineate glacier margins, calculate glacier area, and track glacier change in the Glacier National Park region. This approach allows for inventories that meet the needs of different stakeholder groups who are interested in different subsets and area cutoff criteria depending on their focus, interest, and needs. The table below enumerates glaciers according to different groups: named, comprehensive (including unnamed glaciers), > 0.1 km2, > 0.01 km2. The alternative 0.01 km2 size threshold includes very small glaciers in accordance with the Randolph Glacier Inventory, a global database that international scientists use to calculate ice volume and model glacier dynamics.
These distinct glacier inventories serve various scientific purposes. The “named glaciers” subset and > 0.1 km2 area cutoff remains consistent with previous USGS studies and supports inquiry focused on this recognized group of glaciers. The comprehensive “all glaciers” inventory and smaller > 0.01km2 threshold captures the spatial distribution of all glaciers in the park and can be used to estimate overall hydrologic contribution of water stored in ice.
Glacier margin time series and area change assessments are relatively straightforward to generate when adequate aerial or satellite imagery is available. However, these metrics of documenting glacier change are limited, because tracking the glacier’s footprint does not account for glacier thinning or thickening. Capturing that vertical dimension of change requires elevation data. Pairing glacier area change with glacier surface elevation change allows for volume loss estimates. This information provides researchers with a more hydrologically significant understanding of the magnitude of glacier loss in complete three dimensional space, not just at the glacier perimeter. Ongoing USGS research uses satellite imagery and photogrammetry to quantify glacier volume change across the region rather than only at individual glacier sites.
- GNP Glacier Inventory Data – digitized glacier margins derived from aerial and satellite imagery (shp files and metafile)
- Glacier Area InformationTable - named glaciers of GNP and Flathead National Forest (also see PDF directly below)
WHAT DOES THE FUTURE HOLD? Forecasting the future of glaciers involvesmodel development.Previous USGS geospatial modelingforecast premature demise for the glaciers in Glacier National Park because these models did not account for existing ice volume and other physical factors that control glacier response to warming.More recent researchled by the World Heritage Programme forecast 21stcentury glacier fate across United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage sites. This physical modeling predicts near total Glacier National Park glacier disappearance by 2100.USGS analysisshows that localized factors such as ice thickness, shading, and wind effects may mediate the exact timing of ice disappearance, yet the small size of the glaciers in Glacier National Park provides little buffer against a warming climate. This contrasts the modeled outcome for larger glaciers, which persist beyond 2100 in climate scenarios where greenhouse gas emissions are mitigated. Ongoing USGS research will continue to monitor the glaciers at Glacier National Park and other glacierized ecosystems in North America.
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REFERENCES:
USGS Products
1. Martin-Mikle, C.J., andfa*gre, D.B., 2019,Glacier recession since the Little Ice Age: Implications for water storage in a Rocky Mountain landscape:Arctic, Antarctic, and Alpine Research, v:51, p:280-289, https://pubs.er.usgs.gov/publication/70208603.
2. fa*gre, D.B., McKeon, L.A., Dick, K.A., and Fountain, A.G., 2017, Glacier margin time series (1966, 1998, 2005, 2015) of the named glaciers of Glacier National Park, MT, USA: U.S. Geological Survey data release, https://doi.org/10.5066/F7P26WB1.
Non-USGS Products
3. Bosson, J.B., Huss, M., and Osipova, E., 2019,Disappearing world heritage glaciers as a keystone of nature conservation in a changing climate: Earth’s Future, v:7, p:469–479.
RelatedLinks:
- USGS Glacier Retreat Fact Sheet
- Time series of GNP Glacier Retreat
- USGS Repeat Photography Project
- Overview of Glacier National Park’s Glaciers (NPS)
- USGS Benchmark Glaciers
- Global Land Ice Measurementsfrom Space
- Randolph Glacier Inventory
- World Glacier Monitoring Service
- National Park Service RepeatPhotography Teacher Trunk
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