 |
|
|
Sperry Glacier in summer NPS photo |
|
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 Hemispere 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 one called Garden Wall, mark places where two or more glaciers meet. Craggy "horns" are mountaintops scraped vertical on their sides. Just below their summits, smaller glaciers today continue the process of ice-cream-scooping ampitheaters 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 sorts and rounds materials depending on its speed 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 1850, Glacier Park had 150 glaciers. Today there are 37, totalling 9596 acres of perennial ice. Since the ice ages stopped 10,000 years ago, there have been many slight climate shifts causing periods of glacier growth or melt-back. The latest warm period, peaking in worldwide temperature as you read this, could be cause for worry. World-wide, glaciers are a fairly good indicator of world-wide temperature fluctuations. They are being studied in Glacier Park to correlate them to the latest global warming trends. What roles do human activities play in the current trend? Could we cope with severe regional climate shifts and rising sea levels? Glaciers in the park may be able to tell us whether we have to answer those questions. Stay tuned. If the current warming trend continues in Glacier National Park, there will be no glaciers left here in 30 years. Somehow, "Formerly Glacier National Park" doesn't have the same glamour...
|
|
|
