Event Name : Augustine Tephra B
|Start: 390 || Years BP C-14 (raw) || |Description:
From Beget and others (1994): "The next lower tephra occurs from 22 to 64 cm below the top of cores, depending on localized sedimentation rates, and is correlated here with tephra layer "B" from Mount St. Augustine in the southernmost part of Cook Inlet. Field studies at Mount St. Augustine (Siebert and others, 1989) showed that the West Island debris avalanche occurred about 367+/-55 yr B.P., and Beget (1989) showed that the 30-50-cm-thick pumiceous air-fall layer B tephra on Augustine Island was erupted at about the same time [note that more recently, Waitt and Beget (1996) indicate that the West Island debris avalanche occurred after tephra layer B, thus the West Island debris avalanche has been entered in to the database separately]. Conversion of the age of layer "B" and the West Island debris avalanche to calendar years using the approach of Stuiver and Becker (1986) yields a calibrated age of about 1490 A.D., indicating these eruptions occurred ca. 500 years ago. The discovery of Layer "B" from Mount St. Augustine at Skilak Lake demonstrates that this prehistoric tephra was distributed at least 200 km north of the source volcano, and provides an important chronologic datum, allowing estimates of the age of younger tephras in the Skilak Lake cores by interpolation and sedimentation rate estimates."
From Waitt and Beget (2009): "Of the two youngest coarse tephras, M drifted south and B strongly northeast (fig. 7 [in original text])."
"On the south and west, tephra M seems everywhere much thicker than tephra B."
"The two major Augustine proximal tephras that are also identified in distal locations are tephra B (about 390 yr B.P.) and tephra I (about 1,700 yr B.P.). Tephra I is about 3 cm thick at a distance of 110 km, and B is about 7 mm thick at a distance of 200 km (fig. 8 [in original text])."
The Global database on large magnitude explosive volcanic eruptions (LaMEVE; accessed 2017) reports a magnitude of 4, bulk eruptive volume of 0.100 cubic km and a dense rock equivalent eruptive volume of 0.040 cubic km for the eruption.