Yes, there are glaciers in Montana, primarily tucked away in the highest elevations of the state’s western mountain ranges. These ice masses are dynamic features of the high alpine environment, existing where winter snowfall consistently exceeds summer melt. Their presence is a defining characteristic of the Montana Rockies, marking them as a region shaped by glacial forces both past and present. The remaining glaciers are generally small and clustered in specific, protected cirques, or bowl-shaped depressions.
What Defines a Glacier
A true glacier is defined by a set of criteria that confirm its sustained existence and movement. It is a persistent body of dense ice that forms on land where the annual accumulation of snow is greater than the loss from melting and sublimation, a process known as ablation. The weight of overlying snow compresses the snowflakes, transforming them first into granular ice (névé), and then into a denser substance known as firn.
This compaction process eventually creates glacial ice, characterized by its internal movement. Once the ice mass reaches a depth of approximately 30 meters, the pressure causes the ice crystals at the bottom to deform and flow plastically under their own weight. This slow, continuous movement distinguishes a true glacier from a permanent, stagnant snowfield or ice patch.
Primary Locations of Glaciers in Montana
The majority of Montana’s contemporary glaciers are located within the Lewis and Livingston Ranges of the Northern Rocky Mountains. Historically, the region held an estimated 150 glaciers around 1850, at the end of the Little Ice Age. While the concentration of ice features draws attention to Glacier National Park, other high-elevation areas also harbor significant ice masses.
The Absaroka-Beartooth mountains in south-central Montana represent another major concentration, containing approximately 35% of all perennial snow and ice features. These ice bodies, such as Sky Top Glacier on Granite Peak or Grasshopper Glacier, are often found in high-elevation cirques. Specific examples in the northern ranges include Grinnell Glacier and Sperry Glacier.
Measuring the Retreat
Tracking the status of Montana’s glaciers requires rigorous monitoring to determine changes in their area and volume over time. The U.S. Geological Survey (USGS) uses historical context from the mid-19th century, when glaciers were at their maximum size, as a baseline for comparison. Modern assessments rely heavily on remote sensing, utilizing aerial photography and satellite imagery taken in late summer when seasonal snow is minimal.
These methods allow scientists to quantify the loss of glacial area across multi-decade time spans. Data collected between 1966 and 2015 show that named glaciers in the northern ranges have shrunk by an average of 39% in area. Boulder Glacier, for example, saw an area reduction of nearly 85% during that same period. Ice masses that no longer meet the minimum size criteria (generally 100,000 square meters) are reclassified as stagnant ice patches because they lack the capacity for sustained movement.
Ecological Significance
The persistence of these glaciers plays a distinctive role in the local ecology. Glaciers and perennial snowfields provide a sustained release of cold meltwater during the late summer months, when other water sources in the high country often diminish. This constant input of frigid water is important for maintaining the temperature of high-altitude streams and rivers.
The cold-water environment is necessary for the survival of numerous aquatic species, including native salmonids such as the threatened bull trout and the westslope cutthroat trout. Certain invertebrate species are uniquely adapted to these icy habitats, like the meltwater stonefly (Lednia tumana), which is found only in the streams immediately downstream of glaciers. As the glaciers continue to retreat, the loss of this reliable source of cold water threatens to destabilize these specialized aquatic ecosystems.