32 Lavas of Mount Mazama – Dacites

The Geology and Petrography of Crater Lake National Park, 1902

 PART I.

MOUNT MAZAMA.

LAVAS OF MOUNT MAZAMA.a

DACITES.

Dacites are much less abundant than andesites in the rim of Crater Lake, but unlike the basalts, they come from the same general vent. They are very unequally distributed. One flow is on the southern slope some distance from the summit; the others are along the northern crest of the rim and are later than the andesites, excepting only the andesite of Wizard Island. The separate flows to be considered are those of Sun Creek, Cloud Cap, Grouse Hill, Llao Rock, Wineglass, and Cleetwood Cove. Among them there is wide variation, from obsidian through spherulitic to well-banded and largely crystalline material, while some are mud flows streaked with black glass.

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