Alaska Volcano Observatory

Nathlie Mountain hornblende dacite intrusion (Pleistocene). Yellowish-gray, massive, porphyritic dacite (fig 4) that locally displays well-developed columnar joints. Phenocrysts consist of strongly zoned (An15-55) plagioclase (7-15%, as large as 4 mm) highly altered hornblende (1-4%, as long as 3 mm), hypersthene (trace to 1%, 0.5 mm), and rare quartz in cavities, in microfelty groundmass of plagioclase and mafic, opaque, and alteration minerals.

Sample Location:

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	Red (Warning)
	Orange (Watch)
	Yellow (Advisory)
	Green (Normal)
	Uninstrumented

300 km

200 mi

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References Cited

[1] Geologic map of the Gulkana A-1 Quadrangle, south-central Alaska, 1994

Richter, D. H., Duffield, W. A., Sawyer, D. A., Schmoll, H. R., and Ratte, J. C., 1994, Geologic map of the Gulkana A-1 Quadrangle, south-central Alaska: U.S. Geological Survey Geological Quadrangle Map GQ 1728, unpaged, 1 sheet, scale 1:63,360.

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