Brief History of Glaciers in Glacier National Park

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The history of glaciation in Glacier National Park spans thousands of years of glacial growth and recession, carving the steep and striking mountain features we see today. Glaciers have been present within the  boundaries of present-day Glacier National Park since as early as 6,500  years ago (Munroe and others, 2012). These modest glaciers varied in size, tracking climatic trends, but did not grow to their Holocene maximum size until the end of the Little Ice Age,  around A.D. 1850.  The lateral and terminal moraines deposited on the landscape are still visible today and document the maximum Little Ice Age glacier extent (Martin-Mikle and Fagre, 2019). Like glaciers around the globe, the alpine glaciers of Glacier National Park have decreased in size and number during the 20th century in response to climate change.

Logan Glacier, 2005

Glacial moraines, the rocky debris piles left when glaciers retreat, allow scientists to estimate the size of glaciers at end of the Little Ice Age. (USGS, Public domain.)

Approximately 20,000 years ago, the Glacier National Park landscape was almost entirely encased in ice, with glaciers filling mountain valleys and extending onto the plains (Carrara, 1989). All but the tallest peaks were covered by glaciers. By approximately 11,500 years ago the Glacier National Park landscape was nearly ice free (Porter and others, 1983).

Climate reconstructions representative of the Glacier National Park region extend back multiple centuries and show numerous long-duration drought and wet periods that influenced the mass balance of glaciers (Pederson and others, 2004). Of particular note was an 80-year period (~1770-1840) of cool, wet summers and above-average winter snowfall that led to a rapid growth of glaciers just prior to the end of the Little Ice Age (Munroe and others, 2012).

Tree-ring based climate records and historic photographs indicate the initiation of frontal recession and glacier thinning between A.D. 1860 and 1880. Decadal-scale climate anomalies in the early 20th century produced a period of glacial recession somewhat analogous to conditions experienced over the past few modern decades. The coupling of hot, dry summers and low winter snowpack  produced recession rates as high as 100 m/yr from A.D. 1917-1941 (Pederson and others, 2004).

Swiftcurrent Glacier, Glacier National Park

Swiftcurrent Glacier, Glacier National Park from the National Agricultural Imagery Program. Aerial imagery is analyzed to document how the glacier’s area has changed over time. The Little Ice Age extent of Swiftcurrent Glacier is denoted by the red line. (From Martin-Mikle and Fagre, 2019) (Public domain)

 Weather data from Montana between 1950- 2015 show that Montana’s average annual temperature has increased by 2.7°F (1.5°C), while annual maximum and minimum temperatures have increased approximately 3.3°F (1.8°C) (Whitlock and others, 2017).  Glacier retreat in Glacier National Park is documented by USGS scientists working with the Climate Change in Mountain Ecosystems (CCME) group. Analysis of historic topographic maps and modern satellite imagery shows retreat of every named glacier from 1966 to 2015 (Fagre and others, 2017).  Published results of these analyses are available here (https://www.sciencebase.gov/catalog/items?q=ccme-glaciers). 

 

Related Links

USGS FACT SHEET:  Glacier Retreat in Glacier National Park, Montana

National Park Service glaciers

 

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