Drum Tetlin Tephra
Start: 627500 yBP ± 47700 Years [1]
Event Type: Explosive
- Tephrafall [1]
- Lava dome [1]
Description: From Schaefer (2002): "Tephra sample 96TOK-1-9 (Tetlin Tephra), in the lower part of the section has an age of 627.5+/-47.7 ka (40Ar/39Ar age of hornblende, this study)...this tephra does not correlate definitively with any tephras that have been dated in interior Alaska or the Yukon..."
"The thickness of the Tetlin Tephra indicates its deposition was the result of a large explosive eruption. Its composition (highly inflated pumice with abundant euhedral hornblende) matches that of the hornblende dacites described on Mount Drum (Richter and others, 1994). The results of 40Ar/39Ar dating indicate that the deposition of the Tetlin Tephra occurred approximately 627 ka. Based on published geologic descriptions and geochemistry of the Wrangell volcanic field, the most likely candidates for proximal correlation are the 650 to 400 ka silicic domes that are found on the east and southeast flank of Mount Drum volcano."
"Based on age and composition, the 650 to 400 ka eruptive sequence of Mount Drum is the most likely source for the 627-ka Tetlin Tephra. Between 650 and 400 ka, a group of four silicic domes were emplaced on the east and southeast flank of the volcano (K-Ar whole rock ages by Richter and others, 1994). These rhyodacite domes are porphyritic, consisting of brown hornblende, plagioclase, and rare to common hypersthene, biotite, and augite, much like the composition of Tetlin Tephra. All rocks analyzed from Mount Drum have type II rare earth element characteristics: they are LREE-enriched, having La/Yb between 9 to 25 (Richter and others, 1994). No other Wrangell source vents have documented eruptive products or the right age constraints to match the age and composition of the Tetlin Tephra other than the Mount Drum domes. The Tetlin Tephra likely represents an early explosive phase of activity associated with the emplacement of these 650 to 400 ka, petrologically similar domes."
"The thickness of the Tetlin Tephra indicates its deposition was the result of a large explosive eruption. Its composition (highly inflated pumice with abundant euhedral hornblende) matches that of the hornblende dacites described on Mount Drum (Richter and others, 1994). The results of 40Ar/39Ar dating indicate that the deposition of the Tetlin Tephra occurred approximately 627 ka. Based on published geologic descriptions and geochemistry of the Wrangell volcanic field, the most likely candidates for proximal correlation are the 650 to 400 ka silicic domes that are found on the east and southeast flank of Mount Drum volcano."
"Based on age and composition, the 650 to 400 ka eruptive sequence of Mount Drum is the most likely source for the 627-ka Tetlin Tephra. Between 650 and 400 ka, a group of four silicic domes were emplaced on the east and southeast flank of the volcano (K-Ar whole rock ages by Richter and others, 1994). These rhyodacite domes are porphyritic, consisting of brown hornblende, plagioclase, and rare to common hypersthene, biotite, and augite, much like the composition of Tetlin Tephra. All rocks analyzed from Mount Drum have type II rare earth element characteristics: they are LREE-enriched, having La/Yb between 9 to 25 (Richter and others, 1994). No other Wrangell source vents have documented eruptive products or the right age constraints to match the age and composition of the Tetlin Tephra other than the Mount Drum domes. The Tetlin Tephra likely represents an early explosive phase of activity associated with the emplacement of these 650 to 400 ka, petrologically similar domes."
References Cited
[1] Stratigraphy, major oxide geochemistry, and 40Ar/39Ar geochronology of a tephra section near Tok, Alaska, 2002
Schaefer, J. R. G., 2002, Stratigraphy, major oxide geochemistry, and 40Ar/39Ar geochronology of a tephra section near Tok, Alaska: University of Alaska Fairbanks unpublished M.S. thesis, 62 p.
full-text PDF 2.06 MB Complete Eruption References
Stratigraphy, major oxide geochemistry, and 40Ar/39Ar geochronology of a tephra section near Tok, Alaska, 2002
Schaefer, J. R. G., 2002, Stratigraphy, major oxide geochemistry, and 40Ar/39Ar geochronology of a tephra section near Tok, Alaska: University of Alaska Fairbanks unpublished M.S. thesis, 62 p.
full-text PDF 2.06 MB 
Geological and seismological evidence of increased explosivity during the 1986 eruptions of Pavlof Volcano, Alaska, 1991
McNutt, S. R., Miller, T. P., and Taber, J. J., 1991, Geological and seismological evidence of increased explosivity during the 1986 eruptions of Pavlof Volcano, Alaska: Bulletin of Volcanology, v. 53, n. 2, p. 86-98.
