Two active landslides at and near the retreating front of Barry Glacier at the head of Barry Arm Fjord in southern Alaska 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. 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. Interferometric synthetic aperture radar (InSAR) investigations of the area between May and November, 2020, revealed a second, smaller landslide (referred to as Landslide B) on the south-facing slope about 2 km up the glacier from Landslide A. Landslide-generated tsunami modeling in 2020 used a worst-case scenario where the entire mass of Landslide A (about 455 M m3) would rapidly enter the water. The use of multiple landslide volume scenarios 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. This map could form at least a partial basis for discriminating multiple volume scenarios (for example, a separate scenario for each kinematic element). We mapped landslide structures and kinematic elements at scale of 1:1000 using high-resolution lidar data acquired by the Alaska Division of Geological and Geophysical Surveys (DGGS) on June 26, 2020 and high resolution bathymetric data acquired by the National Oceanic and Atmospheric Administration (NOAA) in August, 2020. The predominate structures in both landslides are uphill- and downhill-facing normal fault scarps. 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. One major kinematic element, herein named the Wedge, forms Landslide B. Kinematic element boundaries are a result of cumulative, differential patterns and amounts of movement that 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. In this data release, we include GIS files for the structural and kinematic map; metadata files for mapped structural features; and portable document files (PDFs) of a location map, and the structural and kinematic map at a scale of 1:5000. Lidar and bathymetric data used to map landslide structures will be released by DGGS and NOAA in 2021.

The maps in this data release show active landslide structures in three areas along the north flank of the Slumgullion landslide. After the entire active part of the landslide was mapped in 1992 and 1993 (Fleming and others, 1999), we remapped these three smaller areas at roughly decadal intervals. Our goal was to learn what structures might persist and how they might change as heterogeneous landslide material of variable thickness passed through the areas. Together with the original 1999 map, these maps provide snapshots of the deformational features at converging and diverging margins of the landslide at four periods in about a 30-year time span (1992-2023). During summer months in 2002, 2013, and 2023, we conducted 1:1000-scale mapping using a traditional technique of manually drawing lines on topographic base maps to represent the structures we observed in the field. There was generally a lapse of two or more years between acquisition of the topographic base data and the field mapping. Meters of landslide displacement during the lapse resulted in a mismatch between the topographic map and topography on the active landslide at the time of our fieldwork. When drawing features on the topographic base, we referenced fixed topographic features directly north of the active landslide’s strike-slip boundary to compensate for the mismatch. The data are recorded in Geographic Information System (GIS) files that contain the line styles used to portray and distinguish the different landslide structures. The files record the shapes and positions of the mapped landslide structures. An index of line styles used to portray mapped structures is shown in Figure 1. Topographic base maps used for the 2002, 2013, and 2023 structural maps were from 2000, 2011, and 2018, respectively. One-meter Digital Elevation Models (DEMs), contours, and shaded-relief maps from these three years are included in this data release. The 2000 DEM was created from 2 m contours of the landslide on July 31, 2000, as originally published in Messerich and Coe (2003). The 2011 DEM was created by the authors using a structure-from-motion photogrammetric method and 1:6000 scale aerial photos acquired on September 23, 2011. The 2018 DEM is lidar data collected between October 5, 2018 and September 24, 2019, with the original data available from the U.S. Geological Survey 3DEP Lidar Explorer (U.S. Geological Survey, 2024). The contour interval used for the 2000 DEM is 2 m. The contour interval used for the 2011 and 2018 DEM is 1 m. All GIS data are projected in the Universal Transverse Mercator (UTM) zone 13N cartesian coordinate system. Portable Document Format (PDF) files of the landslide structure maps of each area in 2002, 2013, and 2023, are also provided. Figure 1. Line and polygon types used for landslide structures and features mapped at the Slumgullion landslide. References Fleming, R.W., Baum, R.L., and Giardino, Marco, 1999, Map and description of the active part of the Slumgullion Landslide, Hinsdale County, Colorado: U.S. Geological Survey Geologic Investigations Series Map I-2672 , scale 1:1,000, https://doi.org/10.3133/i2672 Messerich, J.A. and Coe, J.A., 2003, Topographic map of the active part of the Slumgullion landslide on July 31, 2000, Hinsdale County, Colorado: U.S. Geological Survey Open-File Report 03-144, 7 p., 1:1,000 scale map. http://pubs.usgs.gov/of/2003/ofr-03-144/ U.S. Geological Survey, 2024, 3DEP Lidar Explorer, data available at: http://prd-tnm.s3.amazonaws.com/index.html?prefix=StagedProducts/Elevation/1m/Projects/CO_Southwest_NRCS_2018_D18

The maps in this data release show active landslide structures in three areas along the north flank of the Slumgullion landslide. After the entire active part of the landslide was mapped in 1992 and 1993 (Fleming and others, 1999), we remapped these three smaller areas at roughly decadal intervals. Our goal was to learn what structures might persist and how they might change as heterogeneous landslide material of variable thickness passed through the areas. Together with the original 1999 map, these maps provide snapshots of the deformational features at converging and diverging margins of the landslide at four periods in about a 30-year time span (1992-2023). During summer months in 2002, 2013, and 2023, we conducted 1:1000-scale mapping using a traditional technique of manually drawing lines on topographic base maps to represent the structures we observed in the field. There was generally a lapse of two or more years between acquisition of the topographic base data and the field mapping. Meters of landslide displacement during the lapse resulted in a mismatch between the topographic map and topography on the active landslide at the time of our fieldwork. When drawing features on the topographic base, we referenced fixed topographic features directly north of the active landslide’s strike-slip boundary to compensate for the mismatch. The data are recorded in Geographic Information System (GIS) files that contain the line styles used to portray and distinguish the different landslide structures. The files record the shapes and positions of the mapped landslide structures. An index of line styles used to portray mapped structures is shown in Figure 1. Topographic base maps used for the 2002, 2013, and 2023 structural maps were from 2000, 2011, and 2018, respectively. One-meter Digital Elevation Models (DEMs), contours, and shaded-relief maps from these three years are included in this data release. The 2000 DEM was created from 2 m contours of the landslide on July 31, 2000, as originally published in Messerich and Coe (2003). The 2011 DEM was created by the authors using a structure-from-motion photogrammetric method and 1:6000 scale aerial photos acquired on September 23, 2011. The 2018 DEM is lidar data collected between October 5, 2018 and September 24, 2019, with the original data available from the U.S. Geological Survey 3DEP Lidar Explorer (U.S. Geological Survey, 2024). The contour interval used for the 2000 DEM is 2 m. The contour interval used for the 2011 and 2018 DEM is 1 m. All GIS data are projected in the Universal Transverse Mercator (UTM) zone 13N cartesian coordinate system. Portable Document Format (PDF) files of the landslide structure maps of each area in 2002, 2013, and 2023, are also provided. Figure 1. Line and polygon types used for landslide structures and features mapped at the Slumgullion landslide. References Fleming, R.W., Baum, R.L., and Giardino, Marco, 1999, Map and description of the active part of the Slumgullion Landslide, Hinsdale County, Colorado: U.S. Geological Survey Geologic Investigations Series Map I-2672 , scale 1:1,000, https://doi.org/10.3133/i2672 Messerich, J.A. and Coe, J.A., 2003, Topographic map of the active part of the Slumgullion landslide on July 31, 2000, Hinsdale County, Colorado: U.S. Geological Survey Open-File Report 03-144, 7 p., 1:1,000 scale map. http://pubs.usgs.gov/of/2003/ofr-03-144/ U.S. Geological Survey, 2024, 3DEP Lidar Explorer, data available at: http://prd-tnm.s3.amazonaws.com/index.html?prefix=StagedProducts/Elevation/1m/Projects/CO_Southwest_NRCS_2018_D18

Steep glacial and paraglacial landscapes often exhibit evidence of gravitationally-driven slope deformation. In recently deglaciated coastal environments, catastrophic failures of these bedrock instabilities as rapid landslides have the potential to generate tsunamis that may pose hazards for communities, infrastructure, mariners, and important natural and cultural resources. We present a first inventory of manually mapped bedrock instabilities in western Prince William Sound and nearby locations in the Chugach Mountains. Slope instabilities included in this inventory are defined as large areas (> 0.01 km2) that exhibit evidence of slope deformation, including scarps, tension cracks, and signs of recent smaller-scale landslides. Areas of repeat rock avalanches, that may indicate areas of larger deformation, are also included. All instabilities in this inventory were identified from a combination of field observations, satellite and airborne optical imagery, InSAR (interferometric synthetic aperture radar)-derived elevation models, and limited local lidar elevation models. This inventory is not exhaustive or complete, nor should it be considered a statistically representative sample of instabilities in this region. Furthermore, it is our intention to continue to add records to this inventory as previously unidentified instabilities are discovered or develop in changing conditions. The data presented here represent bedrock instabilities in western Prince William Sound identified prior to February 2023.

Steep glacial and paraglacial landscapes often exhibit evidence of gravitationally-driven slope deformation. In recently deglaciated coastal environments, catastrophic failures of these bedrock instabilities as rapid landslides have the potential to generate tsunamis that may pose hazards for communities, infrastructure, mariners, and important natural and cultural resources. We present a first inventory of manually mapped bedrock instabilities in western Prince William Sound and nearby locations in the Chugach Mountains. Slope instabilities included in this inventory are defined as large areas (> 0.01 km2) that exhibit evidence of slope deformation, including scarps, tension cracks, and signs of recent smaller-scale landslides. Areas of repeat rock avalanches, that may indicate areas of larger deformation, are also included. All instabilities in this inventory were identified from a combination of field observations, satellite and airborne optical imagery, InSAR (interferometric synthetic aperture radar)-derived elevation models, and limited local lidar elevation models. This inventory is not exhaustive or complete, nor should it be considered a statistically representative sample of instabilities in this region. Furthermore, it is our intention to continue to add records to this inventory as previously unidentified instabilities are discovered or develop in changing conditions. The data presented here represent bedrock instabilities in western Prince William Sound identified prior to February 2023.

The Alaska Division of Geological & Geophysical Surveys (DGGS) used aerial lidar to produce a classified point cloud and high-resolution digital terrain model (DTM), digital surface model (DSM), and intensity model of the Barry Arm landslide, northwest Prince William Sound, Alaska, during near snow-free ground conditions on June 26, 2020. The survey's goal is to provide high quality and high resolution (0.10 m) elevation data to assess potential landslide movement. Aerial lidar and ground control data were collected on June 26, 2020, and subsequently processed in Terrasolid and ArcGIS. Ground control was collected on June 26, 2020, as well. This data collection is released as a Raw Data File with an open end-user license. All files can be downloaded free of charge from the Alaska Division of Geological & Geophysical Surveys website (http://doi.org/10.14509/30593).

Subaerial landslides at the head of the Barry Arm fjord in south-central Alaska could generate tsunamis if they rapidly failed into the fjord and are therefore a potential threat to people, marine interests, and infrastructure throughout the Prince William Sound region. Knowledge of ongoing landslide movement is essential to understanding the threat posed by the landslides. Because of the landslides’ remote location, field-based ground monitoring is challenging. Alternatively, periodic acquisition and interferometric processing of satellite-based synthetic aperture radar data provide an accurate means to remotely monitor landslide movement. Here, we present the interferometric results of tasked RADARSAT-2 satellite synthetic aperture radar data. Data were acquired from two ultrafine beam modes, U19 and U15, that are acquired over the landslide every 24-days, between May 21, 2021 and November 5, 2021.These products were created following the same methodology as described in Schaefer et al. (2020), which provides InSAR data for the same landslides in 2020.

Subaerial landslides at the head of the Barry Arm fjord in south-central Alaska could generate tsunamis if they rapidly failed into the fjord and are therefore a potential threat to people, marine interests, and infrastructure throughout the Prince William Sound region. Knowledge of ongoing landslide movement is essential to understanding the threat posed by the landslides. Because of the landslides’ remote location, field-based ground monitoring is challenging. Alternatively, periodic acquisition and interferometric processing of satellite-based synthetic aperture radar data provide an accurate means to remotely monitor landslide movement. Here, we present the interferometric results of tasked RADARSAT-2 satellite synthetic aperture radar data. Data were acquired from two ultrafine beam modes, U19 and U15, that are acquired over the landslide every 24-days, between May 21, 2021 and November 5, 2021.These products were created following the same methodology as described in Schaefer et al. (2020), which provides InSAR data for the same landslides in 2020.

This data release contains extent shapefiles for 16 hypothetical slope failure scenarios for a landslide complex at Barry Arm, western Prince William Sound, Alaska. The landslide is likely active due to debuttressing from the retreat of Barry Glacier (Dai and others, 2020) and sits above Barry Arm, posing a tsunami risk in the event of slope failure (Barnhart and others, 2021). Since discovery of the landslide by a citizen scientist in 2020, kinematic structural elements have been mapped (Coe and others, 2020) and ground-based and satellite synthetic aperture radar (SAR) have been used to track ongoing movement at a high spatial resolution (Schaefer and others, 2020; Schaefer and others, 2022). These efforts have revealed complex, zonal movement; the mechanisms of which remain unknown. To support hazard assessment, we constructed 16 different failure scenarios. The scenarios are all based on structural elements and/or remotely sensed evidence of motion but are also intended to cover a range of shapes and volumes of material such that different modes of failure and subsequent tsunami wave behavior can be modeled. Extents are presented in ESRI shapefile (.shp) format. Each shapefile has a Slip Angle field and a Sequence field. The Slip Angle field records the horizontal direction of failure (0 degrees = north). In some cases, a multi-phase failure is delineated, e.g., where the failure of part of the landslide might destabilize an additional upslope component. In these instances, an ordinal sequence of failure is specified in the Sequence field. These extents were manually digitized on lidar (1-meter horizontal resolution; Daanen and others, 2021) and SAR imagery (2–3-meter horizontal resolution; Schaefer and others, 2020; Schaefer and others, 2022) to align with either mapped kinematic components of the landslide or clear edges of motion identified by coherent synthetic aperture radar signals. As such they are subjective, based on expert opinion and current best available data. References Cited Barnhart, K.R., Jones, R.P., George, D.L., Coe, J.A., and Staley, D.M., 2021, Preliminary assessment of the wave generating potential from landslides at Barry Arm, Prince William Sound, Alaska: U.S. Geological Survey Open-File Report 2021–1071, 28 p., https://doi.org/10.3133/ ofr20211071. Coe, J.A., Wolken, G.J., Daanen, R.P., and Schmitt, R.G., 2021, Map of landslide structures and kinematic elements at Barry Arm, Alaska in the summer of 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P9EUCGJQ. Daanen, R.P., Wolken, G.J., Wikstrom Jones, Katreen, and Herbst, A.M., 2021, Lidar-derived elevation data for upper Barry Arm, Southcentral Alaska, June 26, 2020: Alaska Division of Geological & Geophysical Surveys Raw Data File 2021-1, 9 p. https://doi.org/10.14509/30589. 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. 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: U.S. Geological Survey data release, https://doi.org/10.5066/P9Z04LNK. Schaefer, L.N., Coe, J.A., and Wolken, G.J., 2022, Interferometric synthetic aperture radar data from 2021 for landslides at Barry Arm Fjord, Alaska: U.S. Geological Survey data release, https://doi.org/10.5066/P9QJ8IO4.

This data release contains extent shapefiles for 16 hypothetical slope failure scenarios for a landslide complex at Barry Arm, western Prince William Sound, Alaska. The landslide is likely active due to debuttressing from the retreat of Barry Glacier (Dai and others, 2020) and sits above Barry Arm, posing a tsunami risk in the event of slope failure (Barnhart and others, 2021). Since discovery of the landslide by a citizen scientist in 2020, kinematic structural elements have been mapped (Coe and others, 2020) and ground-based and satellite synthetic aperture radar (SAR) have been used to track ongoing movement at a high spatial resolution (Schaefer and others, 2020; Schaefer and others, 2022). These efforts have revealed complex, zonal movement; the mechanisms of which remain unknown. To support hazard assessment, we constructed 16 different failure scenarios. The scenarios are all based on structural elements and/or remotely sensed evidence of motion but are also intended to cover a range of shapes and volumes of material such that different modes of failure and subsequent tsunami wave behavior can be modeled. Extents are presented in ESRI shapefile (.shp) format. Each shapefile has a Slip Angle field and a Sequence field. The Slip Angle field records the horizontal direction of failure (0 degrees = north). In some cases, a multi-phase failure is delineated, e.g., where the failure of part of the landslide might destabilize an additional upslope component. In these instances, an ordinal sequence of failure is specified in the Sequence field. These extents were manually digitized on lidar (1-meter horizontal resolution; Daanen and others, 2021) and SAR imagery (2–3-meter horizontal resolution; Schaefer and others, 2020; Schaefer and others, 2022) to align with either mapped kinematic components of the landslide or clear edges of motion identified by coherent synthetic aperture radar signals. As such they are subjective, based on expert opinion and current best available data. References Cited Barnhart, K.R., Jones, R.P., George, D.L., Coe, J.A., and Staley, D.M., 2021, Preliminary assessment of the wave generating potential from landslides at Barry Arm, Prince William Sound, Alaska: U.S. Geological Survey Open-File Report 2021–1071, 28 p., https://doi.org/10.3133/ ofr20211071. Coe, J.A., Wolken, G.J., Daanen, R.P., and Schmitt, R.G., 2021, Map of landslide structures and kinematic elements at Barry Arm, Alaska in the summer of 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P9EUCGJQ. Daanen, R.P., Wolken, G.J., Wikstrom Jones, Katreen, and Herbst, A.M., 2021, Lidar-derived elevation data for upper Barry Arm, Southcentral Alaska, June 26, 2020: Alaska Division of Geological & Geophysical Surveys Raw Data File 2021-1, 9 p. https://doi.org/10.14509/30589. 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. 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: U.S. Geological Survey data release, https://doi.org/10.5066/P9Z04LNK. Schaefer, L.N., Coe, J.A., and Wolken, G.J., 2022, Interferometric synthetic aperture radar data from 2021 for landslides at Barry Arm Fjord, Alaska: U.S. Geological Survey data release, https://doi.org/10.5066/P9QJ8IO4.