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Griggs reported activity



Event Name : Griggs 3460 yBP

Start: 3460 (± 40 Years) Years BP C-14 (raw)

Tephrafall: BibCard
Lava dome: BibCard
Eruption Type:Explosive

Description: From Fierstein (2007):"Mount Griggs, fumarolically active and moderately productive during postglacial time (mostly andesitic lavas), has three nested summit craters, two of which are on top of a Holocene central cone. Only one ash has been found that is (tentatively) correlated with the most recent eruptive activity on Griggs (<3,460 14C years B.P.)."

"One tephra layer found on lower slopes of Mount Griggs (K-2419 in Griggs Fork of Knife Creek) may be correlative with lava from the innermost (youngest) crater at Griggs summit."

"Although Griggs has been moderately productive during postglacial time and is relatively better preserved than many stratovolcanoes in the region, only one tephra has been identified that correlates compositionally with Griggs lavas. Preserved in a gully at the south foot of the volcano, only 4 km SE of the summit, the ash includes magnetite with distinctively high TiO2 (12-15% TiO2) that is similar to magnetite from a small knob (that might be a 50-m-dome) within the innermost (and youngest) crater on Mount Griggs (Fig. 7b [in original text]). If this correlation is correct, the ash records the most recent eruptive activity on Griggs. A radiocarbon date on soil 4-7 cm beneath this ash is 3,460+/-40 14C years B.P."

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