Status of Glaciers in Glacier National Park

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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.

Map of named glaciers of Glacier National Park

 Location of named glaciers greater than 0.1 km2 within the boundary of Glacier National Park in 1966 (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%.

USGS glacier inventory data for glaciers within the boundary of Glacier National Park Data

USGS glacier inventory data for glaciers within the boundary of Glacier National Park Data (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?

Repeat photographs of Grinnell Glacier (1911, top image and 2016, bottom image)

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

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.

 

 

 

 

 

 

 

 

WHAT DOES THE FUTURE HOLD? Forecasting the future of glaciers involves model developmentPrevious USGS geospatial modeling forecast 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 research led by the World Heritage Programme forecast 21st century 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 analysis shows 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.

Figure of modeled fate of glaciers

Glaciers of Glacier National Park are projected to disappear by the end of the 21st century, regardless of future representative concentration pathways (RCP). Whereas the magnitude demise of glaciers in the larger Olympic National Park varies by emission scenario. The solid line shows the mean of 14 Global Climate Models and the shaded area shows uncertainty (+/- 1 standard deviation). The y-axis shows ice volume relative to 2017 estimates. (Figure modified from Bosson et al. (2019); see reference (3) below).  

REFERENCES:

USGS Products

1. Martin-Mikle, C.J., and Fagre, 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. 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., 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.

Related Links: 

 

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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.)

 

Area of the Named Glaciers of Glacier National Park (GNP) and Flathead National Forest (FNF) at Little Ice Age maximum extent, 1966, 1998, 2005 and 2015 

 

These data represent a time series of the 37 named glaciers of Glacier National Park, MT, USA and two named glaciers in the Flathead National Forest. Glaciers on this 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. Establishing rates of glacier retreat using the decreasing area of glacier ice is key to understanding the Glacier National Park ecosystem and future state of resources.

Glacier margins were digitized from late-summer aerial and satellite imagery to capture glacier margins when seasonal snow was least present on the glacier surface.  The glacier’s maximum extent during the peak of the Little Ice Age (LIA, mid-nineteenth century) was determined from moraines visible in satellite imagery. Specific image sources are available in the cited data releases. Completion of this named glacier time series revealed that in some cases the 1966 data extend beyond LIA data. This prompted reanalysis of the original 1966 aerial imagery against modern high-resolution imagery and geologic evidence. Any necessary corrections of the 1966 glacier maps are ongoing and will be available in a forthcoming data publication.

Data Summary:

  • Comparison between years shows every named glacier reduced in area from LIA extent to 2015/6, although rates of loss are variable.
  • Moraines indicate that 82 glaciers >0.1 km2 existed in and near GNP during the LIA
  • The 2015 data reveal that  26 named glaciers remain >0.1 km2 (25 acres)
  • The mean reduction in named glacier area between 1966 and 2015 was 40%
  • The mean reduction in named glacier area between LIA and 2015 was 68%
  • Glacier Area Data - Printable PDF
Table depicting Area of the Named Glaciers in National Park and Forest

Area of the Named Glaciers of Glacier National Park and Flathead National Forest at Little Ice Age maximum extent, 1966, 1998, 2005 and 2015 (Credit: USGS. Public domain.)

Salamander and Jackson glaciers were not initially named as separate glaciers until retreat fragmented these glaciers from Grinnell and Blackfoot glacier respectively. Topographic ledges were used to distinguish these as separate features, for the purposes of intercomparison and consistency with previously published named glacier data. Subsequent time stamps in the time series show clear and distinct glacier fragmentation.

Italicized glacier names identify glaciers that are no longer >0.1 kmby 2015

 

Data Sources:

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://dx.doi.org/10.5066/F7P26WB1.

Fagre, D.B., and Martin-Mikle, C.J., 2018, Maximum glacial extent of the named glaciers in Glacier National Park during the peak of the Little Ice Age: U.S. Geological Survey data release, https://www.sciencebase.gov/catalog/item/5b194f1ce4b092d965237f5f.

 

Related Links:

Time Series of Glacier Retreat

USGS Glacier Research

GNP Glacier Inventory Data

Glacier recession since the Little Ice Age: Implications for water storage in a Rocky Mountain landscape

Retreat of Glaciers in Glacier National Park factsheet

 

 

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