Studies of Hydrothermal Processes in Crater Lake, Oregon – extracted from OSU College of Oceanography Report #90-7
Crater Lake sits within the caldera of Mt. Mazama, a center of volcanism in the Oregon Cascades for more than 400,000 years. The morphology of the lake is largely a consequence of a climactic eruption that occurred 6845 + 50 years ago; however, intercaldera volcanism took place as recently as 4000 years ago. The volcanic morphology provides a basin for what is now the deepest lake in the United States (approximately 590 meters). The volcanic terrain strongly limits the nutrient fluxes into the lake, mostly because the lake covers 78% of the total drainage area. Consequently, the lake is highly oligotrophic and one of the clearest lakes in the world.
Our studies of Crater Lake began as an attempt to understand the important physical and chemical characteristics of the lake and the processes which produced some unusual sediment compositions, consistent with hydrothermal inputs to the lake. Given the location of the lake directly above a relatively recent and major magmatic source, thermal spring input to the lake would not be surprising. Such a source was first suggested by the USGS scientist Van Denburgh in 1968, who noted the relatively high sulfate and chloride content of Crater Lake as compared to nearby Davis Lake, and suggested that these two constituents ” …. may have been contributed to the lake by thermal springs or fumaroles, probably located below the present lake level. Such springs and fumaroles are a common expression of hydrothermal activity at a site of volcanic eruptions.”