21 Given the caldera with water-tight walls

Geological History of Crater Lake

Given the caldera with water-tight walls, there is no difficulty in forming Crater Lake, for in that region precipitation is greater than evaporation. Extensive observations upon precipitation and evaporation have not been made at Crater Lake, but, judging from those made at nearest points, the annual precipitation should be between 60 and 70 inches, while the annual evaporation is about 46 inches. The average diameter of the lake is nearly 5 miles. Its area, including Wizard Island, is about 21.30 square miles. The drainage area inclosed by the rim of the lake, according to Mr. E. C. Barnard, is 27.48 square miles. During the winter great masses of snow drift within the rim, and thus considerably augment the normal precipitation of the lake. The lake does not fill up and overflow. The surplus water must have a subterranean outlet, probably toward the southeast, where the region is traversed by extensive breaks in the rocks, and abounds in excellent springs.

The color of the lake is deep blue, excepting along the borders, where it merges into various shades and tints of green. It is so transparent that even on a hazy day a white dinner plate 10 inches in diameter may be seen at a depth of nearly 100 feet. The fish it contains have been introduced. A small crustacean flourishes in its waters, and salamanders occur in abundance locally along the shore.

The level of the lake oscillates with the seasons. During the rainy winter it rises, and in the summer it falls. In August, 1896, observations were made for 22 days, and the lake sank at the rate of 1 inch for every five or six days, depending somewhat on the conditions of the weather. The Mazamas have established a water gauge, and it was hoped that an extended series of observations would be obtained, but the ice broke it off the next winter, The annual oscillation of the lake is about 4 feet.

The temperature of Crater Lake has been the subject of considerable investigation. While the earlier observations appeared to indicate that the lake received heat from its bottom, later observations show that the temperature of the lake everywhere below a depth of 300 feet is approximately 39° and the bottom contains no appreciable volcanic heat.

Aside from its attractive scenic features, Crater Lake affords one of the most interesting and instructive fields for the study of volcanic geology to be found anywhere in the world. Considered in all its aspects, it ranks with the Grand Canyon of the Colorado, the Yosemite Valley, and the Falls of Niagara, but with an individuality that is superlative.

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