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Map of landslide structures and kinematic elements at Barry Arm, Alaska in the summer of 2020

February 9, 2021

Two active landslides at and near the retreating front of Barry Glacier at the head of Barry Arm Fjord in southern Alaska (Figure 1) could generate tsunamis if they failed rapidly and entered the water of the fjord. Landslide A, at the front of the glacier, is the largest, with a total volume estimated at 455 M m3 (Dai et al, 2020). Historical photographs from Barry Arm indicate that Landslide A initiated in the mid twentieth century, but there was a large pulse of movement between 2010 and 2017 when Barry Glacier thinned and retreated from about 1/2 of the toe of Landslide A (Dai et al., 2020). The glacier has continued to retreat since 2017. Interferometric synthetic aperture radar (InSAR) investigations of the area between May and November, 2020, revealed a second, smaller landslide (referred to as Landslide B, Figure 1) on the south-facing slope about 2 km up the glacier from Landslide A (Schaefer et al., 2020). Landslide-generated tsunami modeling by Dai et al. (2020) used a worst-case scenario where the entire mass of Landslide A (about 455 M m3) would rapidly enter the water. InSAR results from 2020 indicated that internal parts (kinematic elements) of Landslides A and B underwent spatially and temporally variable movement (Schaefer et al., 2020). The use of multiple kinematic elements (and their associated volumes) in future tsunami modeling efforts would be beneficial in evaluating tsunami risk to communities in the Prince William Sound region. Herein, we present a map of landslide structures and kinematic elements within, and adjacent to, Landslides A and B (Figure 2). This map could form at least a partial basis for discriminating multiple volume scenarios (for example, a separate scenario for each kinematic element) for future tsunami modeling. We mapped landslide structures and kinematic elements at scale of 1:1000 using high-resolution (0.1 m) lidar data acquired by the Alaska Division of Geological and Geophysical Surveys (DGGS) on June 26, 2020 (DGGS, 2020) and high resolution (4 m) bathymetric data acquired by the National Oceanic and Atmospheric Administration (NOAA) in August 2020 (NOAA, 2020). The predominate structures in both landslides are uphill- and downhill-facing normal fault scarps (Figure 2). Uphill-facing scarps dominate in areas where downslope extension from sliding has been relatively low. Downhill-facing scarps dominate in areas where downlslope extension from sliding has been relatively high. Strike-slip and oblique-slip faults form the boundaries of major kinematic elements. Four major kinematic elements, herein named the Kite, the Prow, the Core, and the Tail, are within, or adjacent to, Landslide A (Figure 3). One major kinematic element, herein named the Wedge, forms Landslide B (Figure 3). These major kinematic elements could be further sub-divided into smaller elements, but this subdivision was not done as part of this data release. Kinematic element boundaries are a result of cumulative, differential patterns and amounts of movement that likely began at inception of the landslides. Elements and/or their boundaries may change location as the landslides continue to evolve. Kinematic elements mapped in 2020 may or may not reflect patterns of historical short-term, episodic movement, or patterns of movement in the future. We were not able to field check our mapping in 2020 because of travel restrictions due to the COVID-19 pandemic. We hope to field check the mapping in the summer of 2021. This data release includes GIS files for the structural and kinematic map (Barry_Arm_Data.zip); metadata files for mapped structural features (summary_metadata.xml and Barry_Arm_Data.zip); and figures of a location map (Figure1.jpg), the structural and kinematic map at a scale of 1:5000 (Figure2.jpg), and a simplified map of major kinematic elements and their relation to Landslides A and B (Figure3.jpg). We also include a high-resolution georeferenced pdf of the structural and kinematic map (Figure2.pdf). Lidar data used to map landslide structures was released by DGGS in February, 2021 (Daanen et al., 2021). Bathymetric data used to map landslide structures will be released by NOAA in 2021. References Cited Daanen, R.P., Wolken, G.J., Wikstrom Jones, Katreen, and Herbst, A.M., 2021, High-resolution lidar-derived elevation lidar data for Barry Arm landslide, Southcentral Alaska, June 26, 2020: Alaska Division of Geological & Geophysical Surveys Raw Data File 2021-3, 9 p. https://doi.org/10.14509/30593 Dai, C., Higman, B., Lynett, P.J., Jacquemart, M., Howat, I.M., Liljedahl, A.K., Dufresne, A., Freymueller, J.T., Geertsema, M., Ward Jones, M. and Haeussler, P.J., 2020, Detection and assessment of a large and potentially?tsunamigenic periglacial landslide in Barry Arm, Alaska: Geophysical Research Letters, 47(22), e2020GL089800. https://doi.org/10.1029/2020GL089800 DGGS, 2020, Barry Arm landslide and tsunami hazard: DGGS web site, https://dggs.alaska.gov/hazards/barry-arm-landslide.html, accessed January 17, 2021 NOAA, 2020, NOAA bathymetric data helps scientists more accurately model tsunami risk within Barry Arm: News & Updates Blog, Office of Coast Survey, https://nauticalcharts.noaa.gov/updates/noaa-bathymetric-data-helps-sci… accessed January 17, 2021 Schaefer, L.N., Coe, J.A., Godt, J.W., and Wolken, G.J., 2020, Interferometric synthetic aperture radar data from 2020 for landslides at Barry Arm Fjord, Alaska (ver. 1.4, November 2020): U.S. Geological Survey data release, https://doi.org/10.5066/P9Z04LNK