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At the Foot of an Alluvial Fan Muncho Lake, British Columbia, Canada |
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The northernmost ranges of the Rocky Mountains flank Muncho Lake: the forested Terminal Range to the west and the barren Sentinel Range to the east, both rising about 5000 feet above the lake. Sudden intense storms, especially in summer, produce flash floods which, with no vegetation to protect the ground, wash down huge amounts of sand, gravel and boulders. Once the floodwaters burst out of the narrow canyons the torrent is free to turn in any direction, spreading the alluvium in a fan-shaped deposit. Alluvial fans are characteristic of desert areas, such as Death Valley, so it is intriguing to see them here, almost on the border of the Yukon. But the causes are the same, here and in the desert — a steep mountain front, lack of vegetation to hold the surface, and occasional intense precipitation. The blue-green color of Muncho Lake is normal for a glacially fed stream or lake — but there are no glaciers near Muncho Lake. In this case, apparently, it is due to copper oxide in the water. Next: Stone Mountain |