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.

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.

Permafrost is integral to the landscape of the Yukon, and influences hydrology and ecology, and impacts infrastructure. Accelerated permafrost thaw due to climate change poses significant challenges, particularly for the Alaska Highway, a vital transportation route. This study investigates how thawing permafrost may relate to ground instability, resulting in cracks and deformations along the highway. Thermal infrared imaging, and light detection and ranging (lidar) mounted on remotely piloted aircraft systems (RPAS), along with ground surveys, were completed at three localities along the Alaska Highway between the White River and the community of Beaver Creek, Yukon. Through these surveys, temperature variations and topographic changes were examined. At many locations, the damage is characterized by a 1 to 2 m-wide subsidence feature running longitudinally along the middle of the highway. Associated with these zones of subsidence are potholes, as well as longitudinal and transverse cracks. In places, the system of cracks extends to the edge and shoulder of the highway, suggesting that the cracks and deformation are currently active features.

Fire can be a significant driver of permafrost change in boreal landscapes, altering the availability of soil carbon and nutrients that have important implications for future climate and ecological succession. However, not all landscapes are equally susceptible to fire-induced change. As fire frequency is expected to increase in the high latitudes, methods to understand the vulnerability and resilience of different landscapes to permafrost degradation are needed. Geophysical and other field observations reveal details of both near-surface (<1 m) and deeper (>1 m) impacts of fire on permafrost along 11 transects that span burned-unburned boundaries in different landscape settings within interior Alaska. Data collected along the 11 transect locations include: electrical resistivity tomography (ERT), downhole nuclear magnetic resonance (NMR), active layer thickness (ALT), organic layer thickness (OLT), and plant species cover. These geospatial datasets are the foundation for the journal article: Minsley, B. J., N. J. Pastick, B. K. Wylie, D. R. N. Brown, and M. Andy Kass (2016), Evidence for nonuniform permafrost degradation after fire in boreal landscapes, J. Geophys. Res. Earth Surf., 121, 320–335, doi:10.1002/2015JF003781.

Fire can be a significant driver of permafrost change in boreal landscapes, altering the availability of soil carbon and nutrients that have important implications for future climate and ecological succession. However, not all landscapes are equally susceptible to fire-induced change. As fire frequency is expected to increase in the high latitudes, methods to understand the vulnerability and resilience of different landscapes to permafrost degradation are needed. Geophysical and other field observations reveal details of both near-surface (<1 m) and deeper (>1 m) impacts of fire on permafrost along 11 transects that span burned-unburned boundaries in different landscape settings within interior Alaska. Data collected along the 11 transect locations include: electrical resistivity tomography (ERT), downhole nuclear magnetic resonance (NMR), active layer thickness (ALT), organic layer thickness (OLT), and plant species cover. These geospatial datasets are the foundation for the journal article, "Evidence for non-uniform permafrost degradation after fire in boreal landscapes", published in the Journal of Geophysical Research - Earth Surface.

Fire can be a significant driver of permafrost change in boreal landscapes, altering the availability of soil carbon and nutrients that have important implications for future climate and ecological succession. However, not all landscapes are equally susceptible to fire-induced change. As fire frequency is expected to increase in the high latitudes, methods to understand the vulnerability and resilience of different landscapes to permafrost degradation are needed. Geophysical and other field observations reveal details of both near-surface (less than 1 m) and deeper (greater than 1 m) impacts of fire on permafrost along 11 transects that span burned-unburned boundaries in different landscape settings within interior Alaska. Data collected along the 11 transect locations include: electrical resistivity tomography (ERT), downhole nuclear magnetic resonance (NMR), active layer thickness (ALT), organic layer thickness (OLT), and plant species cover. These geospatial datasets are the foundation for the journal article, "Evidence for non-uniform permafrost degradation after fire in boreal landscapes", published in the Journal of Geophysical Research - Earth Surface.

With assistance from the Yukon Oil and Gas Branch, EDI Environmental Dynamics Inc. developed and submitted a proposal to the Mining and Petroleum Environmental Research Group (MPERG) to conduct a study of vegetation regeneration on linear developments subject to wildfires, specifically on and in the vicinity of the winter access road leading to test well site K- 58, beginning in the first post-fire growing season. The study site was located in sub-arctic, black spruce (Picea mariana) dominated forest in a zone of continuous permafrost in the area of Eagle Plains, YT. The study examined vegetation composition and abundance, as well as soil and permafrost conditions, in four types of linear disturbances, including: 1) burned 30+ year old seismic lines; 2) a burned one-year-old winter road; 3) the same burned one-year-old winter road constructed on an existing, 30+ year old seismic line, and; 4) unburned 30+ year old seismic lines. A total of 73 (200m2) paired vegetation plots were completed within each of the above linear disturbances and adjacent forests. Overall, the vegetation was highly uniform among all types of linear disturbances and undisturbed sites in the study area. Differences in species composition and abundance were most pronounced between the burned and unburned sites, with a greater number of species present and higher vegetation cover in unburned sites. Of the three types of linear disturbances sampled, the combined disturbance of the burned one year old winter road constructed on a 30+ year old seismic line demonstrated the most notable differences in vegetation composition and abundance in comparison with the adjacent forest. In contrast, species composition and abundance in the burned winter road and burned 30+ year old seismic line were more similar to that in adjacent, burned forests. No trends in soil moisture were detected among the various disturbance types. Depth to permafrost was slightly lower in all three linear disturbances, but this difference was not significant. Depth of organic soil was significantly lower in the combined disturbance of the burned one year old winter road constructed on a 30+ year old seismic line, and was significantly higher in the burned winter road, when compared to adjacent, burned forests. Moss depth was significantly higher in unburned than burned sites. In the first post-fire year, this recent burn appears to be the dominant factor affecting vegetation composition and abundance in the study area. Re-vegetation is occurring rapidly on linear disturbances, with the dominant vascular plant species in the unburned, undisturbed forest regenerating across all disturbance types. Because the study was completed in the first post-fire growing season, it was not possible to assess regeneration of black spruce, an important structural species that is not reported to begin to regenerate until several years after a burn. Similarly, it was also not possible to assess lichen re-establishment, an important element of vegetation succession in black spruce forest that also re-establishes later than the first post-fire growing season. Continued monitoring will be required to understand the longer term response of vegetation to fire in linear disturbances.

A reconnaissance inventory of permafrost-related landslides in the Pelly River watershed was conducted in 2006, largely in response to local community concerns regarding the potential impacts of climate change on slope stability and possible effects on water quality. Using aerial photograph analysis, satellite imagery, and visual inspection from a fixed-wing aircraft, over 100 permafrostrelated slides were located near the Pelly and MacMillan rivers and various tributaries. Basic geomorphic characteristics were determined for many of the failures based on analysis of remote sensing data, and reviews of existing literature and surficial geology maps. Most of the landslides identified were small active-layer detachments and retrogressive thaw failures. Several large failures also illustrate important characteristics associated with permafrost-related landslides, including their source-area setting, triggers, high mobility, the longevity of their activity and their ability to impact very large areas. The nature and distribution of the identified failures highlights a number of implications for land-use in central Yukon and emphasizes the need for enhanced methods of permafrost detection and regional mapping in the Territory.

The following report describes the settings, causes and geological controls of landslides in the Alaska Highway corridor. Although diverse geologic, geomorphic and climatic environments exist in the region, most landslides are related to the presence of shallow bedrock or permafrost, unconsolidated sediment on steep slopes, weak bedrock, groundwater hydrology, river erosion or the degradation of ice-rich permafrost. Where geologic controls provide appropriate settings, intense rainfall, rapid snow melt and seismic events play important roles in triggering failures. Rainstorms that reach thresholds of combined intensity and duration have triggered abundant shallow landslides within the corridor. Debris flows have historically posed the highest risk to lowlying regions and are capable of damaging settlements and transportation routes. The Shakwak Valley has the highest concentration of landslides within the corridor due to the abundance of steep slopes, high relief and widespread discontinuous permafrost. In Wellesley Depression, shallow permafrost and its subsidence has an important influence on slope instabilities. Landslides in the Yukon Plateau primarily relate to the presence of silt- and ice-rich tills on steep valley sides as well as the incision of fine-grained lacustrine terraces in valley bottoms. Debris flows after intense rainfall events are the most common form of landslide in the Kaska Mountains. Finally, in Liard Lowland, failures associated with glacial meltwater and modern stream incision are the most common landslide events. Permafrost plays an important role in landslide processes in the corridor due to its influence on soil moisture, drainage and strength. Slopes composed of icy sediment that have been burned by forest fires are particularly vulnerable to rapid mass movements due to permafrost degradation. The consequences of the dramatic increase in landslide potential after fire should be considered in local fire management plans. The climate¿s local and regional influence on hydrology, fire frequency and permafrost distribution greatly affects landslide processes. Current climate change projections call for warmer temperatures and increased precipitation for the Yukon in the next half century. Among the anticipated effects of global warming in southern Yukon, increased incidents of intense snowmelt and/or precipitation events, river migration, permafrost degradation or forest fires may lead to an increase in landslide frequency and/or magnitude within the settings described in this report. The most significant impact of increased landslide activity may not be a direct impact. Rather, increased sediment input from landslides will likely increase stream channel instability and flooding. This would be particularly acute in the vicinity of alluvial and colluvial fan complexes along Kluane Lake where highway maintenance is already a challenge.

The effects of permafrost degradation in Yukon have serious negative implications for the structural integrity of vertical infrastructure. This is especially pertinent for critical buildings such as hospitals, schools, etc., in small communities that are situated on top of warm, ice-rich permafrost. Projections of mean annual air temperature over the next few decades, based on regional climatic models, indicate that air temperature will rise, hastening the thaw of permafrost. The combination of rising of air temperatures and buildings situated on warm permafrost has prompted this investigation into the vulnerability of Yukon Government vertical infrastructure. The application of DC resistivity and ground penetrating radar in conjunction with borehole drilling indicates that in Dawson there is warm ice-rich permafrost beneath the Palace Grand Theatre; the Old Territorial Administration building is underlain by primarily unfrozen sediment; and permafrost under the St. Andrew’s Church is characterized by high variability. A deep active layer was observed at Ross River School and geophysical surveys indicate that warm water drainage from the roof is contributing to the thaw of the underlying permafrost.