Status of Glaciers in Glacier National Park

Science Center Objects

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.

Glacial moraines of Logan Glacier

Glacial moraines of Logan Glacier, Glacier National Park (7/30/2005) (Credit: USGS. Public domain.)

WHAT IS A GLACIER? A glacier is 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 bodies are classified as glaciers when their area exceeds 0.1 km2 (100,000 m2), or about 25 acres. 

TRACKING GLACIERS OVER TIME: The extensive valley glaciers that carved GNP’s majestic peaks were 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%.

Map of named glaciers of Glacier National Park

Location of named glaciers of Glacier National Park. Glaciers represented at 1966 size. (Credit: USGS. Public domain.)

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?

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. 

Repeat photographs of Grinnel Glaicer (1911, top image and 2016, bottom image)

Repeat photography documents glacier loss at Grinnell Glacier, 1911 - TW Stanton (USGS), 2016 – L McKeon (USGS)  

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.

 

 

 

WHAT DOES THE FUTURE HOLD?   Researchers recently modeled 21st century glacier response to climate by modeling glaciers across United National Educational, Scientific, and Cultural Organization (UNESCO) World Heritage sites, including those in GNP, providing  an advancement in our understanding of what the future holds for Glacier National Park’s glaciers. Previous geospatial modeling projected premature glacier demise because data limitations did not represent existing ice volume and other factors that influence glacier response to warming . The more recent UNESCO World Heritage study incorporates factors like existing ice volume and suggests that glaciers in GNP will continue to shrink.   Localized factors such as ice thickness, shading, and wind effects may mediate the exact timing of ice disappearance, yet the small size of glaciers like those in Glacier National Park provides little buffer against a warming climate. This contrasts the projected outcome for larger ice masses. For example, glaciers in Olympic National Park are projected to either disappear under high CO2 emission scenario or persist beyond 2100 under mitigated CO2 emission scenarios. 

 

REFERENCES:

USGS Products

1. Chelsea J. Martin-Mikle & Daniel B. Fagre (2019) Glacier recession since the Little Ice Age: Implications for water storage in a Rocky Mountain landscape, Arctic, Antarctic, and Alpine Research, 51:1, 280-289, https://pubs.er.usgs.gov/publication/70208603.

2. Fagre, 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., Osipova, E., 2019. Disappearing world heritage glaciers as a keystone of nature conservation in a changing climate. Earth’s Futur. 7, 469–479. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018EF001139.

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Old Sun Glacier

Old Sun Glacier perched on the side of Mt. Merrit in Glacier National Park. (Credit: John Scurlock (Photographer & Pilot), on behalf of USGS Northern Rocky Mountain Science Center. Public domain.)