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Augustine reported activity





Event Name : Augustine Southeast Beach Debris Avalanche

Start: 760 (± 60 Years) Years BP C-14 (raw)
Stop: 380 (± 20 Years) Years BP C-14 (raw)

Debris-avalanche, volcanic avalanche, or landslide: BibCard BibCard BibCard BibCard
Eruption Type:Not an eruption.

Description: From Waitt and Beget (1996): "Between about 700 and 400 yr B.P. (between tephra layers M and B) a debris avalanche swept to the sea on the west and a small one on the south-southeast. Large lithic pyroclastic flows shed to the southeast; smaller ones descended exiting swales on the southwest and south."

"A boulder diamict exposed in upper part of bluffs along Southeast beach (unit MBas) is studded with angular in situ blocks as large as 2.5 m, as large as 6 m as lag on beach, and as large as 7 m in the surf zone seaward. The diamict is overlain by B tephra and underlain by M and C tephras. These tephras overlie unit HCpe that forms most of bluff. Adjacent lahar or pyroclastic-flow deposits (units MBlp and MBpl) are flatter surfaced and contain angular lithic andesite clasts no larger than 2 m."

"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."

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Page modified: March 30, 2017 14:36
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