48 Inflow of Crater Lake

The Geology and Petrography of Crater Lake National Park, 1902




The drainage area within Mount Mazama is very small as compared with the size of the lake. It is circumscribed by the crest of the rim and limited to its inner slope, with an area, according to Mr. E. C. Barnard, of 27.48 square miles. As the area of the lake, including Wizard Island, is 21.30 square miles, the drainage area encircling the lake is 7.06 square miles—that is, less than one-third of the size of the lake itself. The prevailing southerly and southwesterly winds of winter, when the precipitation is largest and is in the form of snow, greatly increases the catchment over the normal precipitation by drifting snow over the southern rim. It hangs upon the inner slope and furnishes many avalanches to the lake during winter as well as many small streams in summer. Sixty-three small streams were closely estimated or measured by running them over a weir at the end of a trough, and it was found that during the time we were there they added to the lake 10.754 cubic feet per second, or 929,145.6 cubic feet per day. The area of the water surface of the lake is approximately 20.42 square miles, and the water added to the lake in a day, although it seems large in the streams, would raise its surface only 0.00002 foot, an amount which is not appreciable.

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