Sperry Glacier in summer
Glacier National Park is not named so much for its small glaciers, but for the colossal work of colossal glaciers in the past. Ten thousand years ago, the topography of Glacier looked much the same as it does today. Before that, enough ice covered the Northern Hemisphere to lower sea levels 300 feet. In places near the park, ice was a mile deep.
Alpine glaciers don't "bulldoze" landscape as much as they melt and re-freeze, plucking material from areas of snow deposition and moving it to other areas -- like downhill conveyer belts. They don't "retreat", they simply melt in place where warm overwhelms cold at lower elevations. Because the melt / re-freeze cycle happens at the bottoms of glaciers, they scour valleys into a "U" shape, broad at their bases and sheer on their sides. The result is awesome verticality.
Saw-toothed "aretes", like the Garden Wall, mark places where two or more glaciers meet. Craggy "horns" are mountain tops scraped vertical on their sides. Just below their summits, smaller glaciers today continue the process of ice-cream-scooping amphitheaters called "cirques". "Tarns" are the lakes which fill those cirques, often in successively lower strings of bowls. They are called "paternoster lakes" because of their resemblance to rosary beads.
At the other end of the process, terminal and lateral "moraines" form when the conveyer belt pauses, in equilibrium between summer and winter. At a large terminal moraine, glaciers advanced and melted for a few hundred years at exactly the same rate, dumping their payload in one spot. The materials in a moraine tend to be of every size and shape -- ice is indiscriminate about what it can carry. These materials are called "till". Some "erratic" rocks in moraines are the size of houses.
Meltwater, depending on its speed, sorts and rounds materials into layers of boulders, cobbles, pebbles, gravel, sand, silt or clay, in descending order of speed. This "outwash" forms below the terminal end of an alpine glacier.
When a small side-channel glacier feeds into a larger and deeper-cutting trunk glacier, the undercut forms a "hanging valley" like the one above Bird Woman Falls and in hundreds of other places in the park.
In Glacier National Park, scientists are studying the dynamics of glacier recession and the impacts that losing glaciers will have on park ecosystems.Today, the park's glacially fed streams provide a constant flow of cold water throughout the summer season, maintaining necessary water levels and regulating stream temperature for fish and other aquatic species. Plant and animal species throughout the park rely on this flow. However, under current trends of global temperature increase, glaciers here and around the world are rapidly melting. In 1850, Glacier National Park had 150 glaciers. Today, only 25 remain large enough (at least 25 acres in area) to be considered functional glaciers. Since the last ice age ended, around 10,000 years ago, there have been many slight climate fluctuations that have been mirrored by the growth or recession of glaciers. Based on current trends, however, glacier recession models predict that by 2030, Glacier National Park will be without glaciers. Most of the park's glaciers, being of small to moderate size, will likely be gone before then, as many glaciers are retreating faster than their predicted rates.