At the altitude of the crater rim, about eight thousand feet, the diameter is about six miles, the same as that of Mount Shasta at the same altitude. As both peaks are composed of like kinds of lava, we may safely assume that Mount Mazama before it collapsed was about the size and height of Mount Shasta (14,380 feet).
Glacier records furnish additional evidence of the former height and magnitude of Mazama. On the rim and on the outer slopes just below it are a number of glacier grooved and planed rock-surfaces. The lines of these extend downward, so the ice must have come from above. Then, too, there are a number of moraines that show they were deposited by glaciers from upper slopes. Apparently glaciers flowed down all sides of this mountain from a central high point. Two ice-eroded cañons begin in the southern rim and extend down the slope. Plainly these were formed by ice-streams that came down from above. Thus the angle of the lava-built slopes, and the lines of glaciation, testify to the former existence of a high central summit.
On its slopes the Fire King and the Ice King appear to have wrought and to have clashed. Both have vanished from the scene; but here remains a volcanic landscape slightly sculptured by ice. The Mazama story appears a spectacular one.
This scene is a favorite with geologists. They come to it from all over the world. Crater lakes are common. There are numbers of dead craters filled with water in South America, Asia, and elsewhere. But this is an extraordinary crater lake. The marvelous blueness is only one feature. The rare geological exhibit makes a strange appeal.
Joseph S. Diller, of the United States Geological Survey, closes his excellent monograph on the "Geological History of Crater Lake, Oregon" with the following words:—
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 Cañon of the Colorado, the Yosemite Valley, and the Falls of Niagara, but with an individuality that is superlative.
No streams flow into this lake, and there is no visible outlet. It is probable that subterranean waters empty into it and flow from it. The annual precipitation, together with the enormous quantities of snow that are blown into it, greatly exceeds the amount of water evaporated. The water is clear and cold. It is so clear that a plate may be seen upon the bottom through fifty or more feet of water. Fish may be distinctly seen swimming about at great depths.
Many alpine lakes are blue under some lights. The deep blueness of this lake may possibly be due to mineral which the water holds in solution; or also in part to its high surrounding walls and to its enormous depth. Seen from the rim, a narrow margin of the water along the walls is sea-green. Yet a glassful is as clear as the clearest.
By permission of the National Park Service, Department of the Interior