Glacier National Park is a national park of about 4,100 km² (roughly 1,580 sq mi) in north-western Montana, running along the Canadian border where it meets Waterton Lakes National Park in Alberta. Established on 11 May 1910, it straddles the Continental Divide across two sub-ranges of the Rockies, the Lewis and Livingston ranges, and its highest summit is Mount Cleveland at 3,190 m (10,466 ft). It holds more than 700 lakes, the largest being Lake McDonald, about 16 km (10 mi) long. The park takes its name from its small glaciers: of an estimated 150 that existed in the mid-19th century, only 25 were still large enough to count as active by 2010. Together with Waterton the park forms the Waterton-Glacier International Peace Park, the world's first, created in 1932 and listed as a World Heritage Site in 1995. Almost everything that happens here, from when the main road opens to when forests burn, follows the yearly cycle of snow, melt and drought, so this guide follows the park's water year.
Winter on the Continental Divide: Snow That Buries Logan Pass
The water year starts with snow. Precipitation in the park is heaviest in winter and spring, averaging about 50 to 80 mm (2 to 3 in) a month, and at high altitude much of it falls as snow that stays until summer. The two sides of the Divide get very different winters. The western slope, which drains to the Pacific, is lower, milder and wetter, and it collects the biggest snow accumulation. The eastern slope, facing the Great Plains, is higher overall and exposed to long cold waves. That exposure even shows in the trees: the timberline on the east side is almost 244 m (800 ft) lower than on the west.
Weather on the eastern edge can turn with startling speed. In Browning, on the Blackfeet Indian Reservation just east of the park, the temperature fell from 7 °C to −49 °C (44 °F to −56 °F) on the night of 23–24 January 1916, a drop of 56 °C (100 °F) in 24 hours that stands as a world record. On the west side, winter is quieter. Lake McDonald, at 961 m (3,153 ft), lies in a valley filled with cedar and hemlock, the easternmost examples of the Pacific moist forest, and snow lines its shore while the peaks above it carry the season's pack.
That winter snow is the raw material of everything that follows. It feeds the glaciers in their cirques, recharges the lakes and streams, and determines how much water will still be flowing in August. On the alpine tundra above the forests, the snow lasts so long that some ground has as little as three months a year without snow cover.
Spring on the Going-to-the-Sun Road: Ten Weeks of Plowing to the Big Drift
Spring in Glacier is measured by one road. The Going-to-the-Sun Road, built between 1921 and 1932 and formally dedicated on 15 July 1933, is the only route across the park, about 80 km (50 mi) between West Glacier and St. Mary. Halfway along, at 2,026 m (6,646 ft), it tops the Divide at Logan Pass. Up to 24 m (80 ft) of snow can lie on the pass, and more still just east of it, at a snowfield long known as the Big Drift.
Clearing it is one of the hardest plowing jobs in North America. It takes about ten weeks, even with machines that can shift 4,000 tonnes of snow an hour, and on some stretches crews advance as little as 150 m (500 ft) a day. Late-winter avalanches sweep across the road, which is why there are few guardrails on the eastern side: the slides destroyed them. The road is usually open from early June to mid-October. Its latest opening came on 13 July 2022, the latest since the first opening day in 1933.
Melt also sets the human calendar. Once the road is open, the vintage 1930s red buses known as Red Jammers, 33 of the original fleet rebuilt and modernised in 2001, run guided tours over the pass, and the Logan Pass Visitor Center recorded a record 417,824 visitor contacts in 2025. Across the whole park, about 3.5 million people visited in 2019.
Summer Meltwater: Glacial Flour, Triple Divide Peak and 200 Waterfalls
By July the snowpack is running off, and the park's drainage pattern shows itself. Triple Divide Peak, only 2,446 m (8,025 ft) high, sends water into three great drainages: west to the Pacific, north to Hudson Bay and south-east to the Gulf of Mexico. Around 200 waterfalls run at full strength; Bird Woman Falls drops 150 m (492 ft) from a hanging valley beneath Mount Oberlin, and Swiftcurrent Falls tumbles near the Many Glacier Hotel. Later in the season many of them shrink to a trickle.
Glacier melt gives the water its colour. Fine rock ground off by the ice, known as glacial flour, stays suspended in the water, turning Avalanche Lake and Cracker Lake an opaque turquoise and making some streams run milky white. The lakes stay cold all year, rarely warmer than 10 °C (50 °F) at the surface, so little plankton grows and the water is exceptionally clear. Montana gives the park's waters an A-1 rating, its highest. Only 131 of the park's lakes had names as of 2016. Lake McDonald is the deepest, at roughly 140 m (464 to 472 ft depending on the source).
Summer is short and mild. Daytime highs during the tourist season average 16 to 21 °C (60 to 70 °F), nights drop to around 4 °C (40 °F), and snow can fall in any month at altitude. Beargrass flowers widely in July and August. The cold streams hold native westslope cutthroat trout and the threatened bull trout, which anglers must release, while harlequin ducks feed on the lakes and streams. Grizzlies forage across the high meadows: Montana's wildlife agency estimated about 1,051 grizzlies in and around the park in 2021, more than triple the roughly 300 counted when the species was listed as threatened in 1975.
Late-Summer Drought and Fire: From the 64 Fires of 1936 to the 2003 Season
As the snow runs out, the park dries. Less glacial melt means lower stream flow in late summer and autumn and a lower water table, which raises the risk of fire. Fire is a permanent part of the park's year: there has been at least one in every year since 1910 except 1964. The park averages about 14 fires that burn some 20 km² (5,000 acres) each year. The busiest season on record for fire starts was 1936, with 64.
The largest burned area came in 2003. After a five-year drought and a summer with almost no rain, six fires burned about 550 km² (136,000 acres), more than 13 percent of the park, the most since its creation. In 2017 the Sprague Fire burned through Sperry Chalet, leaving only its stone walls; after rebuilding in the summers of 2018 and 2019 it reopened at a ceremony in February 2020. Fire reshapes wildlife too. After a 2001 fire, some park roads were closed the following year so that thousands of western toads could migrate across them.
Dry years add to older stresses on the high forests. White pine blister rust, an introduced fungus, has killed about 30 percent of the whitebark pines in and around the park, and more than 70 percent of the survivors are infected. That matters for wildlife: the pines' fatty seeds feed red squirrels and Clark's nutcrackers, and grizzlies and black bears raid the squirrels' seed caches. Nutcrackers are already less common than they were.
The End of the Melt Season: Grinnell, Sperry and Jackson Glaciers Since 1850
The glaciers show the balance of each year's snowfall against its melt. All the park's present ice dates from the Little Ice Age, roughly 1550 to 1850, rather than from the much larger ice sheets that carved its U-shaped valleys and cirques. After 1850 the glaciers retreated moderately until the 1910s; between 1917 and 1941 some pulled back as fast as 100 m (330 ft) a year. A cooler spell from the 1940s to 1979 slowed the loss, and steady shrinking resumed in the 1980s.
The measurements are stark. Around Blackfoot and Jackson glaciers, ice covered 21.6 km² in 1850 but only 7.4 km² by 1979, a loss of about two-thirds of the area; Jackson, part of Blackfoot when the park was created, is now a separate glacier. Sperry Glacier, on Gunsight Mountain, has lost about 75 percent of its area since the mid-19th century. Grinnell Glacier, on the north flank of Mount Gould in the Many Glacier area, lost almost 40 percent of its area between 1966 and 2005.
How many glaciers remain depends on the definition. The USGS counts a body of ice as a glacier if it covers at least 0.1 km², the size below which ice generally stops moving. By that standard, 35 named glaciers existed at the end of the Little Ice Age and all 35 remained in 1966, but by 2015 only 26 were still large enough. Predictions that every glacier would be gone by 2020 or 2030 were removed from park exhibits as the science advanced; a 2010 study expected Sperry Glacier to persist through at least 2080. Either way, every hectare of ice lost means less meltwater to carry the streams through the dry weeks of late summer. For how the ice formed in the first place, read how glaciers are formed; the park's place in its state and its mountain chain is covered in our guides to Montana's geography and the Rocky Mountains.