Tsunami generation by pyroclastic flow during the 3500-year B.P. caldera-forming eruption of Aniakchak Volcano, Alaska |
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| Authors: | C F Waythomas C A Neal |
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| Institution: | (1) U.S. Geological Survey, Alaska Volcano Observatory, 4230 University Drive, Anchorage, Alaska 99508, USA, US |
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| Abstract: | A discontinuous pumiceous sand, a few centimeters to tens of centimeters thick, is located up to 15 m above mean high tide
within Holocene peat along the northern Bristol Bay coastline of Alaska. The bed consists of fine-to-coarse, poorly to moderately
well-sorted, pumice-bearing sand near the top of a 2-m-thick peat sequence. The sand bed contains rip-up clasts of peat and
tephra and is unique in the peat sequence. Major element compositions of juvenile glass from the deposit and radiocarbon dating
of enclosing peat support correlation of the pumiceous sand with the caldera-forming eruption of Aniakchak Volcano. The distribution
of the sand and its sedimentary characteristics are consistent with emplacement by tsunami. The pumiceous sand most likely
represents redeposition by tsunami of climactic fallout tephra and beach sand during the approximately 3.5 ka Aniakchak caldera-forming
eruption on the Alaska Peninsula. We propose that a tsunami was generated by the sudden entrance of a rapidly moving, voluminous
pyroclastic flow from Aniakchak into Bristol Bay. A seismic trigger for the tsunami is unlikely, because tectonic structures
suitable for tsunami generation are present only south of the Alaska Peninsula. The pumiceous sand in coastal peat of northern
Bristol Bay is the first documented geologic evidence of a tsunami initiated by a volcanic eruption in Alaska.
Received: 3 December 1997 / Accepted: 11 April 1998 |
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| Keywords: | Tsunami deposit Pyroclastic flow Aniakchak caldera Volcanigenic tsunami |
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