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1 November 2014 Geologic Records of Net Littoral Drift, Beach Plain Development, and Paleotsunami Runup, North Sand Point, Olympic Peninsula, Washington, USA
Curt D. Peterson, Virginia L. Butler, James K. Feathers, Kenneth M. Cruikshank
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Abstract

A geologic cross-section was constructed across a narrow late Holocene beach plain in a small southwest-facing pocket beach in North Sand Point. Olympic National Park, Washington, to test hypotheses about net littoral drift, potential tectonic uplift, and paleotsunami runup height. Twenty topographic stations (0–12 m elevation NAVD88) and eight auger core sites (2–5 m depth) were examined to establish the stratigraphic development of the narrow beach plain (120 m width). Existing radiocarbon dates and new optically stimulated luminescence (OSL) analyses were used to establish the onset (∼1.5 ka) and termination (∼0.6 ka) of net beach progradation, confirming net northward littoral drift in latest Holocene time. The anomalous high elevations of the beach plain resulted from an abandoned foredune ridge (9 m elevation) developed above the prograded beach deposits (6 m elevation). No tectonic uplift is required to account for the beach plain elevations. A fine gravel layer (5–30 cm thickness) draped the top of the dune ridge at 7–9 m elevation, but it is not traced to 11–12 m elevation in the adjacent late Pleistocene terrace. The gravel layer is attributed to catastrophic marine surge deposition (10 ± 0.5 m elevation) from a nearfield or locally produced Cascadia paleotsunami at ∼1.3 ka. The short duration of the recorded beach plain progradation (about one thousand years), together with a range of OSL grain bleaching ages (11.1–2.3 ka) that pre-date the beach plain deposition, attest to prior pocket beach instabilities and/or sand recycling in the high wave-energy beaches of the northwest Olympic Peninsula coastline.

© 2014 by the Northwest Scientific Association. All rights reserved.
Curt D. Peterson, Virginia L. Butler, James K. Feathers, and Kenneth M. Cruikshank "Geologic Records of Net Littoral Drift, Beach Plain Development, and Paleotsunami Runup, North Sand Point, Olympic Peninsula, Washington, USA," Northwest Science 88(4), 314-328, (1 November 2014). https://doi.org/10.3955/046.088.0406
Received: 31 January 2014; Accepted: 1 September 2014; Published: 1 November 2014
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