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Edgecumbe reported activity




Event Name : Edgecumbe CFE

Start: 9000 Years BP C-14 (raw)

Tephrafall: BibCard BibCard
Lahar, debris-flow, or mudflow: BibCard
Pyroclastic flow, surge, or nuee ardente: BibCard
Caldera/crater: BibCard
Eruption Type:Explosive
Eruption Product: dacite BibCard

Description: From Kosco (1981): "A pumice eruption associated with the formation of a 1 km caldera marks the end of volcanic activity: this eruption has been radiocarbon dated at 9000 years b.p. (Heusser 1960)."

From Riehle and others (1992): "A tree stump buried by the topmost of several flow deposits on Kruzof Island (site 7, Fig. 1 [in original text]) closely limits the age of one of the latest pyroclastic eruptions. The outer surface is only incipiently charred (R. Hoblitt, written commun.,1990), so it may have been a lahar that buried the stump. A split of outer rind yielded 9180+/-150 and 9150+/-150 yr B.P. (1-12,218 and 1-12,219; Riehle and Brew, 1984).

From Riehle and Brew (1994): "A thin layer of tephra is separated by silt and peat from underlying tephra layers at several stations on Kruzof Island. The layer is a heterogeneous assemblage of dense volcanic rocks and pumice. The pumice contains 72 percent SiO2 in whole-rock and 74 percent SiO2 in the glass and is slightly more siliceous than samples classified herein as dacite (fig. 65 [ in original text]). Maximum thickness (5 cm) and lapilli size (2 cm) occur southwest of Mount Edgecumbe (82-116, 82-117; fig. 64 [in original text]). The deposit is probably the result of a minor eruption of Mount Edgecumbe or Crater Ridge caldera; the pumice could be accessory material from an earlier unknown deposit incorporated in a largely phreatic eruption."

"We found one tree trunk in a dacitic-pumice-bearing lahar deposit (81-74; fig. 64 [in original text]). The piece was vertical and had a frayed top and a flared base resembling the remains of a root system. We think that the tree was killed and transported by a lahar. A split sample yielded 9,180+/-150 and 9,150+/-150 yr B.P. (I-12, 218; I-12, 219)."

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