Radiocarbon, Cesium-137, Grain Size, and X-ray Fluorescence Data for Tsunami Geology Investigation, Driftwood Bay, Umnak Island, Alaska (2018)

Radiocarbon analyses were conducted at the National Ocean Sciences Accelerator Mass Spectrometry Facility, Woods Hole, Massachusetts. Samples for radiocarbon dating were plant macrofossils collected above and below the sand sheets and tephra; they included delicate peat moss (Sphagnum spp) stems and leaves, black stems of sedges (Carex spp), and woody twigs. Calibrated radiocarbon ages were computed from lab-reported ages using OxCal (version 4.2.4) (Bronk Ramsey, 2009) with the IntCal13 data set of Reimer and others, 2013. The C-14 dataset reports one-sigma, analytic ages in radiocarbon years before 1950 (14C yr BP).

Grain size analyses were performed at the USGS Sediment Core Splitting and Description Laboratory, Santa Cruz, California. To determine particle size distributions for bulk sand samples and sub-intervals of the thickest sand sheets, 2 mm and 0.063 mm sieves were used to separate samples into gravel, sand, and mud fractions. The gravel fraction was analyzed using sieves and the sand and mud fractions were analyzed using an LS 13-320 laser diffraction particle size analyzer (Beckman Coulter, Indianapolis) at 1/4 phi size intervals. The grain size distributions were weighed and combined to reflect each fraction's contribution to the total sample weight using pcSDSZ Sediment Size Analysis Software, Stevens and Hubbell, 1986.

Gamma spectroscopy, using low-background, high-efficiency, high-purity Germanium detectors, yielded 137Cs activities in 1-cm-thick sediment intervals sampled within 17 cm of the surface in core 201. Samples were initially dried, homogenized by grinding, packed into standardized vessels, and sealed for at least 24 hours before counting. Activities were corrected for self-absorption using a direct transmission method (Cutshall and others, 1983; Cable and others, 2001).

The X-ray fluorescence (XRF) scanning is a non-destructive technique that uses X-rays to excite electrons in the sample and obtain a near-continuous record of fluorescence energy and wavelength spectra that correspond to the atomic structures of constituent elements of the sample material (Jansen and others, 1998; Wien and others, 2005, Ge and others, 2005). Analyses were performed at Scripps Institution of Oceanography on an Avaatech XRF core scanner (Avaatech, Alkmaar, The Netherlands; Richter and others, 2006) to measure element intensities at the sediment surface of two, split sediment cores: CF103C and CF305A. See Addison and others, 2013 for methods used to prepare sediment surfaces, the X-ray energy levels used in the analyses, and details of data calibration.