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Katmai reported activity





Event Name : Katmai Late Pleistocene Rhyodacite Pumice-Fall and Ignimbrite (LPFI)/Windy Creek Ashflow

Start: 22500 (± 1600 Years) Years BP C-14 (raw)
Stop: 19240 (± 70 Years) Years BP C-14 (raw)

Tephrafall: BibCard
Pyroclastic flow, surge, or nuee ardente: BibCard BibCard BibCard
Eruption Type:Explosive
MaxVEI: 6 BibCard
Eruption Product: rhyolite BibCard

Description: From Stevens (2012): "Deposits of a pre-1912 rhyolitic ashflow are exposed on the west side of lower Windy Creek valley (Figure 4 [in original text]). Hildreth and others (2003) map correlative ashflow deposits in Mageik Creek that are dated to 19,240+/-70 RC yr B.P. and posit that the plinian eruption generating these deposits might have been greater in magnitude than that of 1912. The source of these deposits is probably Mount Katmai (Hildreth and others 2003)."

From Fierstein (2007): "Mount Katmai was also the source of two other large explosive events, one ?23 ka and the other between 12 and 16 ka, the earlier of which was probably larger than that of 1912."

"The largest and most explosive events in the Katmai cluster originated at Mount Katmai within the past 25,000 years: the Plinian rhyodacitic eruption ?23 ka that inundated proximal valleys with thick ignimbrite and widely dispersed fallout..."

"Lithic-rich stratified pumice-fall deposits 7 and 5 m thick along Mageik and Windy Creeks (Fig. 18 [in original text]) are overlain directly by nonwelded ignimbrite at least 75 and 8 m thick, respectively (Hildreth and Fierstein 2003). Lithic and pumice clasts in the fallout are coarse at both locations-as large as 11 cm (lithics) and 14 cm (pumice) in Mageik Creek; pumice clasts to 5 cm in Windy Creek. Pumice clasts in all the emplacement units, mostly white but some medium gray, are nearly unique among products of the Katmai cluster in containing hornblende phenocrysts and in having 72% SiO2; only the most evolved rhyodacite lava on the south rim of Mount Katmai is mineralogically and chemically similar (not identical; Hildreth and Fierstein 2000, 2003). Survival of so few remnants of such thick deposits suggests that emplacement was largely over ice, and the coarse debris flows and thin glacial deposits overlying these pyroclastic remnants suggest a late Pleistocene age. Organic material at the base of the LPFI in Mageik Creek gave an age of 19,240+/-70 14C year B.P., equivalent to a calibrated age of 22.8 ka, which is comparable to the 40Ar/39Ar age (22.5+/-1.6 ka) of the south-rim Katmai lava. The plinian deposit must be very widespread; it probably extends from Kodiak Island to west-central Alaska, but the work has not yet been completed to confirm that. Because the pumice fall is so coarse and thick in Mageik and Windy Creeks (respectively 7-9 km SW and 21 km WNW of the caldera rim) it seems likely that the rhyodacitic eruption was even larger than that of 1912."

The Global database on large magnitude explosive volcanic eruptions (LaMEVE; 2017) reports a magnitude of 6.000, bulk eruptive volume of 10.000 cubic km and a dense rock equivalent eruptive volume of 4.000 cubic km for the eruption.

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Page modified: March 30, 2017 14:36
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