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Roundtop reported activity

ROUNDTOP LINKS

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EVENT SPECIFIC INFORMATION

Event Name : Roundtop 10000 yBP

Start: 10000 Years BP Tephrochronology
Stop: 9100 Years BP Tephrochronology

Tephrafall: BibCard BibCard
Eruption Type:Explosive
Eruption Product: rhyolite BibCard
MaxVEI: 5 BibCard
ChemYes
Otherfelsic

Description: From Carson and others (2002): "This horizon [Horizon B] consists of scattered 1-2 cm pumice lapilli, gray to light brown, dispersed in a 10-15 cm thick sediment horizon. It was collected at seven outcrops in the ColdBay area, on the west and northeast shores of ColdBay at sites 6, 9, 10, 11, 13, 23, and 25 (Fig. 5 [in original text]). At all locations, the horizon was collected either beneath the Funk/Fisher ash or directly above the late Wisconsin diamicton. EMPA of the samples consistently yielded total weight compositions well below 98.0 (e.g. sample 96JF9A from site 6 [in original text], on-line Appendix 1). When oxygen was explicitly analyzed in these samples, total weight percent compositions were ~100.0%, indicating that the anomalously low initial values were the result of hydration of the samples. For these samples alone, the original totals were normalized to 100.0% for comparison and correlation (Froggatt, 1992). The normalized totals represent a horizon with the most silica-rich horizon collected, with ~77 wt% SiO2 (Table 3 [in original text]). Independently of major-element chemistry, the horizon was correlated based on stratigraphic position below the Funk/Fisher ash and on the size of large pumice fragments. Once the EMP values were normalized to 100.0%, the SC values were 0.95-0.98. Although there are no radiocarbon dates directly associated with this horizon, its stratigraphic position indicates it was deposited sometime between the deglaciation of Cold Bay and deposition of the Funk/Fisher ash."

"Horizon B correlates to the proximal samples from the early Holocene eruption of Roundtop volcano (Miller, 1999). The combination of SC=0.95, similar outcrop descriptions of coarse lapilli >1cm in diameter dispersed in sediment, and the stratigraphic position of this deposit below the Funk/Fisher ash demonstrates that Horizon B is the product of an eruption of Roundtop volcano dating to 9100-10,000 14C yr BP."

The Global database on large magnitude explosive volcanic eruptions (LaMEVE; 2017) reports a magnitude of 5, bulk eruptive volume of 7.0 cubic km and a dense rock equivalent eruptive volume of 3.04 cubic km for the eruption.

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Page modified: March 30, 2017 14:36
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