A large earthquake occurring 700–800 years ago in Aialik Bay, southern coastal Alaska

A conifer forest on the shore of Verdant Cove, an inlet of Aialik Bay on the southeast coast of the Kenai Peninsula, Alaska, was buried by high-energy beach sediments shortly after 860 ± 50 I4C years BP. The switch from ocean-distal forest to cobble beach indicates a radical change in depositional environment suggestive of rapid subsidence of 1–3.5 m. The presence of hemlock, a tree taxon sensitive to salt-water exposure, and the preserved cast of a tree trunk suggest that subsidence and burial occurred rapidly. By 690 ± 60 14C years BP, forest peat was accumulating atop the beach sediments burying the forest and rapid spit progradation was underway. Spit progradation implies land emergence or stable sea level, especially in this case where the spit has a limited sediment supply. We infer that subsidence of the spit ca. 860 ± 50 14C years BP was followed by slow land emergence up to the time of the 1964 AD great earthquake, when the area subsided coseismically 1.4 m. The sudden drowning of the buried fore...

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