With increasing development in areas of discontinuous permafrost, greater emphasis is being placed on slope hazard assessment. The current research project was initiated in response to the occurrence of a large flow-type slide, the Magundy River landslide, with the aim of identifying and characterizing slope hazards in the Little Salmon Lake area of the central Yukon. Terrain evaluation studies identified over 35 areas of past and present landslide activity in the project area. Field work was completed in the summer of 2004 to obtain ground truth for the terrain evaluation and to further characterize the most prominent and active landslides. This paper provides an overview of the research project and summarizes observations on four distinct landslide processes found in the Little Salmon Lake area: debris flow, rock slumping, bimodal flow and multiple retrogressive slumping.

The Yukon is experiencing impacts of climate change, marked by elevated annual air temperatures, alterations in precipitation patterns and increased wildfire activity. These changes can lead to permafrost degradation, impacting highways and community Infrastructure. In July 2017, a wildfire burned a slope in permafrost terrain above the Dempster Highway in the Yukon. In the years following the wildfire, two types of permafrost-related landslides have been observed on the slope. Active layer detachment activity was highest in the first year after the landslide, possibly influenced by warm temperatures and rainfall events. Retrogressive thaw flow slides formed in 2019 in areas of ice-rich permafrost and are still active in 2023. Deposition of sediment and influx of water has resulted in flooding near the highway, further degrading the permafrost in the valley bottom. This study characterizes the landslide timing and morphology following a wildfire on permafrost terrain, and investigates potential triggers and controls.

The Aishihik River landslide is a prehistoric slope failure located on a southwest-facing slope of the Ruby Range along the Alaska Highway. The failed mass consists of gneissic material from the Kluane metamorphic assemblage. Shoreline sediments from glacial lake Champagne were deposited on top of the landslide debris, suggesting that the slope failure occurred after the ice retreat but before the Dezadeash valley drained. Three dominant discontinuity sets were recognized and correlated to the fracturing associated with the formation of the Ruby Range antiform. Rock engineering classification and laboratory tests suggest that the rock mass present in the headscarp of the failure is of lower quality than on its sidescarps. This rock mass degradation was attributed to two intersecting fault sets at the headscarp. Tension cracks and trenches are present on all sides of the slope failure. Exposed soil and disturbed vegetation observed in trenches suggest continued instability.

Five case studies of recent landslides in southwestern Yukon Territory illustrate the role of permafrost in landslide processes of the region. In the Marshall Creek basin, permafrost degradation after recent forest fires caused numerous debris flows near the valley bottom. Similarly, on Haeckel Hill, firerelated deepening of the active layer has facilitated active layer detachment slides on upper hillside slopes. In the Kluane Range, the interface between frozen and unfrozen ground appears to control the depth of movement for active layer detachment slides and debris flows along Silver Creek. The failure mechanism on Mount Sumanik is controlled by a frozen substrate, which contributes to a reduction in drainage and elevated pore-water pressure. Lastly, thawing of segregated ice has caused a thaw slump of fine-grained sediment in lacustrine terraces along Takhini River.

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.

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.

This report provides comprehensive documentation of landslide, permafrost subsidence and fluvial erosion-related geohazards for the Yukon portion of the Dempster Highway. It provides Yukon Department of Highways and Public Works – Transportation Engineering Branch a practical geohazard inventory that will help guide planning and mitigate future risk to the highway. It also becomes a valuable reference pertaining to slope stability, permafrost and fluvial processes in northern Yukon. Results from this study identified 54 mass movement geohazards and 102 meander-highway encroachment sites with the potential for future highway impact. Of particular significance, 75% of the mapped mass movement geohazards are influenced by permafrost or degrading permafrost, an important geological attribute considering future temperatures are expected to increase.

During 2008-2010, the Alaska Division of Geological & Geophysical Surveys continued a program, begun in 2006, of reconnaissance mapping of surficial geology in the proposed natural-gas pipeline corridor through the upper Tanana River valley, a 12-mi-wide (19.3-km-wide) area that straddles the Alaska Highway through the upper Tanana River valley from the western boundaries of the Tanacross B-6 and C-6 Quadrangles near the mouth of the Robertson River eastward to the eastern boundaries of the Tanacross A-4 and B-4 Quadrangles near Tetlin Junction. Mapping during 2008-2010 in the Tanacross Quadrangle linked with mapping of surficial geology completed in the Big Delta and Mt. Hayes quadrangles in 2006-2007. Surficial geology was initially mapped in this second corridor segment by interpreting ~1:65,000-scale, false-color, infrared aerial photographs taken in July 1978, August 1980, and July 1983.Verification of photo mapping was accomplished during the 2008-2010 summer field season, when map units were described, soil pits were hand dug, and samples were collected for analyses.

Landslides are common across Southeast Alaska (SEAK) and have caused damages and fatalities in populated areas. Better understanding of landslide triggering conditions and impacts can inform risk reduction strategies and alerting efforts. Landslide inventory data with high temporal resolution (weekly to hourly) are needed to quantify these conditions. Local news sources are a source of landslide information that often report both timing and impacts. Here, we present an inventory of 162 news-reported landslides in SEAK between 1990 and 2024. This data release focuses on landslides reported near seven population centers with long-term meteorological records: Juneau, Haines, Sitka, Petersburg, Wrangell, Prince of Wales Island, and Ketchikan. The inventory was created by searching for the keyword “landslide” in 13 different local news sources. It provides the minimum and maximum date and time of occurrence for each landslide, the closest population center, latitude and longitude, an estimated location accuracy, a description of the location, the landslide type, the potential trigger, and a description of the size and initiation point of each landslide. Where available, the number of fatalities and buildings damaged and a description of the impacts are documented. The primary news source, publication date, and links to news article(s) describing each event are also included. This data release complements existing sources of landslide information in SEAK, for example the Alaska Department of Transportation and Public Facilities Geo Event Tracker (Alaska Department of Transportation and Public Facilities, 2022), the U.S. Forest Service Tongass National Forest Landslide Inventory (U.S. Forest Service, 2024), and the National Oceanic and Atmospheric Administration Storm Events Database (National Centers for Environmental Information, 2020), by providing high temporal resolution and impact descriptions for many of the reported events. This data release includes: (1) a table documenting each landslide with its attributes (SEAK_News_Reported_Landslides.csv) (2) a table with data field definitions and descriptions SEAK_News_Reported_Landslides_Definitions.csv Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.