A glacier is a persistent body of dense ice that is constantly moving under its own weight; it forms where the accumulation of snow exceeds its ablation (melting and sublimation) over many years, often centuries. Glaciers slowly deform and flow due to stresses induced by their weight, creating crevasses, seracs, and other distinguishing features. They also abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water.
On Earth, 99% of glacial ice is contained within vast ice sheets in the polar regions, but glaciers may be found in mountain ranges on every continent except Australia, and on a few high-latitude oceanic islands. Between 35°N and 35°S, glaciers occur only in the Himalayas, Andes, Rocky Mountains, a few high mountains in East Africa, Mexico, New Guinea and on Zard Kuh in Iran.
Glacial ice is the largest reservoir of freshwater on Earth.Many glaciers from temperate, alpine and seasonal polar climates store water as ice during the colder seasons and release it later in the form of meltwater as warmer summer temperatures cause the glacier to melt, creating a water source that is especially important for plants, animals and human uses when other sources may be scant. Within high altitude and Antarctic environments, the seasonal temperature difference is often not sufficient to release meltwater.
Because glacial mass is affected by long-term climate changes, e.g., precipitation, mean temperature, and cloud cover, glacial mass changes are considered among the most sensitive indicators of climate change and are a major source of variations in sea level.
Glacier National Park is a national park located in the U.S. state of Montana, on the Canada–United States border with the Canadian provinces of Alberta and British Columbia. The park encompasses over 1 million acres (4,000 km2) and includes parts of two mountain ranges (sub-ranges of the Rocky Mountains), over 130 named lakes, more than 1,000 different species of plants, and hundreds of species of animals. This vast pristine ecosystem is the centerpiece of what has been referred to as the “Crown of the Continent Ecosystem”, a region of protected land encompassing 16,000 square miles (41,000 km2).
The region that became Glacier National Park was first inhabited by Native Americans. Upon the arrival of European explorers, it was dominated by the Blackfeet in the east and the Flathead in the western regions. Soon after the establishment of the park on May 11, 1910, a number of hotels and chalets were constructed by the Great Northern Railway. These historic hotels and chalets are listed as National Historic Landmarks and a total of 350 locations are on the National Register of Historic Places. By 1932 work was completed on the Going-to-the-Sun Road, later designated a National Historic Civil Engineering Landmark, which provided greater accessibility for automobiles into the heart of the park.
The mountains of Glacier National Park began forming 170 million years ago when ancient rocks were forced eastward up and over much younger rock strata. Known as the Lewis Overthrust, these sedimentary rocks are considered to have some of the finest fossilized examples of extremely early life found anywhere on Earth. The current shapes of the Lewis and Livingston mountain ranges and positioning and size of the lakes show the telltale evidence of massive glacial action, which carved U-shaped valleys and left behind moraines which impounded water, creating lakes. Of the estimated 150 glaciers which existed in the park in the mid-19th century, only 25 active glaciers remained by 2010.Scientists studying the glaciers in the park have estimated that all the glaciers may disappear by 2020 if the current climate patterns persist.
Glacier National Park has almost all its original native plant and animal species. Large mammals such as the grizzly, moose, and mountain goat, as well as rare or endangered species like the wolverine and Canadian lynx, inhabit the park. Hundreds of species of birds, more than a dozen fish species, and a few reptile and amphibian species have been documented. The park has numerous ecosystems ranging from prairie to tundra. Notably, the easternmost forests of western redcedar and hemlock grow in the southwest portion of the park. Large forest fires are uncommon in the park. However, in 2003 over 13% of the park burned.
Glacier National Park borders Waterton Lakes National Park in Canada—the two parks are known as the Waterton-Glacier International Peace Park and were designated as the world’s first International Peace Park in 1932. Both parks were designated by the United Nations as Biosphere Reserves in 1976, and in 1995 as World Heritage sites.