Augustine reported activity

Event Name : Augustine East Point Debris Avalanache

Stop: 2160 (± 60 Years)

Years BP C-14 (raw)

Debris-avalanche, volcanic avalanche, or landslide:

Description: From Waitt and Beget (1996): " Beneath a tephra layer "G" dated at about 2200-2000 yr B.P. lies a coarse, hummocky debris-avalanche deposit along the east coast, the oldest exposed such deposit on Augustine Island."

"A diamict forming the lowest pan of coastal sea cliff for 3 km along the east is at least 13 m thick (base not exposed). It contains angular andesite fragments as large as 5 m; on the beach before the sea cliff are wave winnowed lag boulders as large as 7 m. The large clasts are set in a gravelly-sand matrix of shattered andesite, generally gray but in places oxidized reddish. Most of the boulder-sized andesite clasts are gray, some are reddish, and a few are highly altered to yellow or white. A few delicate prismatically jointed clasts must have been hot juvenile dome-rock clasts that cooled after emplacement."

"The deposit is capped by the sparsely exposed G tephra and that overlain by the lights oxidized boulder diamict of Yellow Cliffs debris-avalanche deposit."

"During this prehistoric period numerous domes must have been emplaced at the summit, repeatedly renewing the source for catastrophic debris avalanches. Remnants of these older domes form the east and south sides of the present summit-dome complex. Below the summit area at least three domes were emplaced on the upper flanks, one on the south (Karnishak dome), two on the northwest (domes "I" and "H"). Another undated and nearly buried dome or lava flow diversifies the upper south flank."