Item: Reconstructing ancient avalanches of the sierra nevada range
Title: Reconstructing ancient avalanches of the sierra nevada range
Proceedings: Proceedings of the 1998 International Snow Science Workshop, Sunriver, Oregon
Authors: P. R. Caterino, AJpengroup
Abstract: The surface elevations of the lakes of the Sierra Nevada have stood considerably lower than the present for extended periods of time. The magnitude of drops in the levels of these lakes is supported by existing paleoenvironmental evidence; by a series of radiocarbon dates on trees drowned by the rising waters, by submerged archaeological features in the lake, and by historical documentation of lower lake levels. This data has implications for local and regional paleoclimatic trends, which in tum affect the existing avalanche influence zones. In lakes ranging from Tenaya Lake, Yosemite National Park, in the southern Sierra Nevada to Lake Tahoe, Donner Lake, and Independence Lake in the northern range, there have been compelling evidence of sustained lower lake levels. Through SCUBA surveys, stumps that have been dated, range from 4,800 B.P. to 6,300 B.P. in Lake Tahoe to 600-700 B.P. in other lakes of the Sierra Nevada. Research supports that during the rise of the lake levels there was a substantial and rapid increase in precipitation, such that the increase in avalanche activity caused the destruction of the forest that appeared during the lower lake elevations (approximately 150 years). Because of the low water temperature and dissolved oxygen rates in these lakes any organic materials that have been rapidly submerged are very well preserved. Many of the trees that were sampled and dated between 60C-700 B.P. still had bark and coloration intact. The submerged avalanche debris fans that are located in 5 to 50 m of water, generally occur within the present day avalanche influence zones.
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Keywords: avalanches, snow cover, snow precipitation
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