Crater Lake

Crater Lake is found in the Cascade Range of southern Oregon. At nearly 2,000 feet, it is the deepest lake in the United States and one of the deepest in the world. The lake lies in the caldera (basin) of a volcano that collapsed following eruption about 7,700 years ago. It is surrounded by steep rock walls as high as 2,000 feet in some locations and is about five miles in diameter.

One of the captivating features of Crater Lake is the vibrant blue color of its water. The depth and purity of the lake produce this unique coloring. The purity is largely attributable to the hydrologic characteristics of the lake. The lake is unique in that it has no inlets or outlets. This means that the main source of water to the lake is direct precipitation. The absence of rivers or streams greatly reduces the deposition of dissolved minerals and sediment into the lake. In addition, seepage from the lake removes minerals that manage to enter the water. The amount of dissolved minerals is limited by the relative insolubility of the volcanic rocks lining the cold water lake.

A body of water’s color depends on water characteristics and solar interactions. Water molecules absorb longer wavelengths of light (red, orange, yellow and green colors) and scatter the shorter wavelengths – shades of blue. This scattered blue light is redirected back to the surface where it is visible. Although blue light is the most readily scattered, the next shortest wavelength, green, also experiences some scattering, particularly in shallows where greenish hues are visible. Particulates, plants and other substances in the water reflect their own unique set of wavelengths to the surface, detracting from the blue light. Therefore, at Crater Lake where most of the water is extremely deep and pure, the blue light doesn’t compete with other wavelengths, giving the water its vibrant blue color.

Related Resources

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Photos: NASA/USGS (Front Page); Stuart Seeger (This Page)