North Cascades National Park
More than any other park in the contiguous United States, North Cascades National Park is dominated by glaciers. Over 300 glaciers, about one-third of the glaciers in the Lower 48 states, are in the 204,278 hectares enclosed within the park boundaries. The glaciers are most evident at the height of summer, when the annual snowfall has melted and only the semi-permanent glaciers remain.
This Landsat image was taken at just such a time, on August 11, 2001, when the valleys were a verdant summer green and the glacier-capped peaks of the Cascades remained white. Everything in the image, from the steep-sloped mountains to the intricate network of streams running out of the mountains, says that the landscape was engineered by ice.
Throughout the image, U-shaped valleys separate the peaks. Such valleys tend to be wide, with a flat valley floor surrounded by steep mountains. Wider valleys are carved by larger glaciers. River-cut valleys, by contrast, tend to have a "V" shape. Rivers and streams draining meltwater from the glaciers now wind through the U-shaped valleys. One of the larger of these is filled with Ross Lake, top center. The lake was created when Ross Dam was built across the Skagit River in the area shown just above the center of the image.
Elsewhere, the very shape of the mountains points to glacial action. Narrow, blade-like ridges, aretes, are bright jagged lines surrounded by shadowed steep slopes. These form when glaciers carve two U-shaped valleys on either side of the ridge. The round, amphitheater shape of some of the ridges occurs when a glacier grinds out a hollow or bowl (a cirque) on the face of the ridge.
Because glaciers are among the most valuable resources in the park and are sensitive to climate change, the United States Geological Survey (USGS) has been monitoring the glaciers since 1993. The scientists use a variety of methods, including stakes that monitor snow accumulation, radar to measure the thickness of the glaciers, and photos that show the boundaries of the glaciers, to determine if the glaciers are growing or shrinking over time. In general, the glaciers have been shrinking, particularly those on the eastern slopes of the mountains.