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Augustine reported activity





Event Name : Augustine Tephra C

Start: 1100 (± 100 Years) Years BP C-14 (raw)

Tephrafall: BibCard BibCard BibCard BibCard BibCard BibCard
Eruption Type:Explosive

Description: From Waitt and Beget (1996): "Exposed on the steeply eroded sides of three south-side inlier kipukas at altitudes 250-700 m are 8-10-m sections comprising several beds of pumiceous and lithic pyroclastic-fiow deposits interbedded with many beds of loose, sorted pumiceous fall deposit. The uppermost pumiceous fall beds probably correlate with tephras M, C, and perhaps with other tephra beds of the coastal sections, though ambiguous field character and ambiguous chemical data make such correlations tenuous. Yet a radiocarbon age of about 2160 yr B.P. (table 2 [in original text]) from the upper midsection (below the upmost few tephra layers) at the eastmost such section supports the tenuous correlation."

From Waitt and Beget (2009): "The lowest five coarse-pumice beds at the coast-tephras G, I, H, C, and O-drifted east and southeast. Tephra G and ambiguous tephra O are known only from a few sites each on the east and southeast, neither with enough data points to warrant a map. Drawn from data at many stratigraphic exposures, isopach maps clearly show tephras I, H, and C drifted east-southeast and southeast."

"Glass separates of tephras C and M are chemically nearly identical-as close as replicate microprobe analyses of either tephra C or tephra M alone. Correlation of tephras between separated localities is thus mainly by field stratigraphy, in some places strengthened or augmented by the microprobe data."

"Tephra C in places comprises three coarse horizons and commonly is a couplet of coarser beds separated by finer material."

From Tappen and others (2009): "Tephra layer C comprises two units including upper (C2) and lower (C1) fall deposits that possibly represent two phases of the same eruption (R. Waitt pers. comm., 2004). Unit C1 is a light gray, coarse-grained, andesitic, normally graded tephra deposit that is 60-70 cm thick and overlies soil. The overlying C2 tephra unit is 12-15 cm thick and shows distinct reverse grading with the largest pumice fragments at the top. Mingling of some prehistoric magmas occurred, because one C2 clast consists of white pumice containing bands of much darker volcanic rock."

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