Geological History of Crater Lake
It has been suggested, but perhaps not in serious thought, that the cone on Wizard Island may represent the summit of the sunken Mount Mazama projecting above the water. To determine the truth of the matter we must cross over to the island. Wizard Island has two portions—an extremely rough lava field and a cinder cone.
These parts may be distinguished in a view of the island from the Watchman but are more distinct in an illustration, figure 26, as seen from the lake. Only a small portion of the lava field is shown in the foreground. The lava is dark and has a much more basaltic look than any seen in the main body of the rim. It has evidently been erupted from the base of the cinder cone in its present position. The cinder cone, too, is a perfect little volcano, with steep symmetrical slopes 763 feet in height, and surmounted by a crater 80 feet deep. A portion of this crater is shown in figure 27. It is so new and fresh that it is scarcely forested, and shows no trace of weathering. Instead of being a part of the sunken Mount Mazama, it is an entirely new volcano built up by volcanic action upon the bottom of the caldera since the subsidence. Were it not for the lake the whole bottom of the caldera could be examined, and it is possible that other small volcanic cones might be found. This suggestion is borne out by the soundings of the lake, which appear to reveal two other cases, but they do not rise to within 400 feet of the surface of the water. It is evident that the volcanic eruptions upon the bottom of the caldera have partially filled it up. Originally it may have been much more than 4,000 feet deep.