17 The glaciation and structure of the rim

Geological History of Crater Lake

The glaciation and structure of the rim clearly establish the former existence of Mount Mazama, but there may well be doubt as to its exact form and size. Judging from the fact that Mount Shasta and the rim of Crater Lake have the same diameter at an altitude of 8,000 feet, and that their lavas are similar, it may with some reason be inferred that Mount Mazama and Mount Shasta were nearly of equal height. The slopes of Mount Shasta may be somewhat steeper than those of the rim of Crater Lake at an equal altitude, but the glaciation of the rim is such as to require a large peak for its source. A restoration of Mount Mazama based on a photograph of the rim of Crater Lake as seen from the south west is shown in figure 20.

diller20
Figure 20. Restoration of Mount Mazama. Vertical and horizontal scales the same. Diagram furnished by Smithsonian Institution.

 

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