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.

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.

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.

Placer mining has over a one hundred year history in the Yukon Territory. The majority of placer mining has taken place in the zone of discontinuous permafrost. Within the discontinuous permafrost zone, vegetated valley flats and north-facing slopes generally are underlain with permafrost. The permafrost thickness is highly variable and may reach depths of 60 meters. The active layer covering the permafrost also varies greatly in thickness. To access gold bearing gravels, the removal of extensive quantities of overburden is usually required. Once this insulative cover is removed, the thermal equilibrium of the permafrost is disrupted and thawing occurs. This affects the stability of soils and vegetation and slope failure may occur. The extent that exposed permafrost melts depends partly on the amount and form of ice content. As melting progresses, the potential for mass movement of soil increases. Melting permafrost usually results in a wetter environment than was initially present, which further affects the natural revegetation process. Bioengineering is the use of living plant materials to perform engineering functions such as erosion control and stabilization of steep slopes. Although bioengineering methods are now commonly used in the stabilization of steep problem slopes in more moderate climates (Polster, 1997), experimentation with these techniques in areas underlain with permafrost is still required. Advantages of using bioengineering systems are that they can be installed without machine access (which in permafrost areas would disturb the site even more), they strengthen with age, and they are less expensive than traditional hard engineering practices.

The Yukon Geological Survey has compiled a collection of papers, theses, reports and maps that describe permafrost in the Yukon. These reports have been footprinted and indexed to make them easier to find spatially. Distributed from [GeoYukon](https://yukon.ca/geoyukon) by the [Government of Yukon](https://yukon.ca/maps) . Discover more digital map data and interactive maps from Yukon's digital map data collection. For more information: [geomatics.help@yukon.ca ](mailto:geomatics.help@yukon.ca)

This report summarizes the results of geological mapping and preliminary petrological studies of an exposure of ultramafic rocks, the Buffalo Pitts Peridotite (BPP), in the eastern Dawson Range, central Yukon. The BPP is characterized by fresh spinel peridotite. Plagioclase mantles on spinel grains are interpreted to have developed during decompressive metamorphism during exhumation from sub-crustal depths to mid- to upper-crustal depths. The peridotite body forms a foliaform lens 580 m by 100 m that is enclosed in and intruded by leucocratic, biotite-garnet-corundum blue orthogneiss.The peridotite and blue corundum orthogneiss are in turn hosted in a north-dipping panel of amphibolite-grade metamorphic rocks that are included in the pericratonic Devono-Mississippian Wolverine Creek metamorphic suite, part of the Yukon-Tanana Terrane. Quartzite, quartz-mica schist and amphibolite with minor marble and calc-silicate units occur largely south of, and structurally beneath the peridotite body. Leucocratic tonalite gneiss, part of the ~357 Ma Selwyn Gneiss, occurs north of, and structurally above the BPP. Tonalite veins intrude the blue corundum orthogneiss and are interpreted as marginal intrusions of the Selwyn orthogneiss. Intrusion of dykes derived from the Selwyn Gneiss requires exhumation and emplacement of the BPP and the enclosing blue corundum orthogneiss in or prior to the earliest Mississippian.

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.

Up to six years of data have been collected at seven stations within Yukon Geological Survey’s permafrost monitoring network between 2008 and 2013. Warm permafrost conditions (>-0.5°C) governed by latent heat effects exist at the Whitehorse, Watson Lake, Ross River School and Dawson School monitoring stations, while average permafrost temperatures in Faro are only marginally cooler at -0.6°C. Mean annual ground temperatures at the Beaver Creek and the Dawson dump forest monitoring stations are much colder at -2.9 and -2.0°C respectively. Most sites show either insignificant or very slight short term permafrost warming trends, although slight cooling is apparent at Ross River School, and rapid warming has occurred at Beaver Creek over the monitoring period. Opportunities to expand the network and collaborate with external parties operating similar monitoring stations should be further explored to facilitate more complete and representative reporting on the thermal state of permafrost in Yukon.

The presence and proper classification of permafrost is essential to mine planning, operation, and abandonment in the Yukon Territory. This paper discusses the current state of practice regarding permafrost delineation and classification, presents information regarding design and monitoring of structures on permafrost (with particular reference to mining), and includes examples of Yukon and other northern mines where permafrost has affected operations. Permafrost in the Yukon is particularly sensitive to disturbance, as it is generally ¿warm¿ and discontinuous. It is therefore extremely critical that planning for new mines include provisions for the proper classification of permafrost on the mine property, as it will directly affect operations and abandonment of the site, with corresponding financial implications.

Results of surficial geology investigations in Wellesley basin and the Nisling Range can be summarized into four main highlights, which have implications for exploration, development and infrastructure in the region: 1) in contrast to previous glacial-limit mapping for the St. Elias Mountains lobe, no evidence for the late Pliocene/early Pleistocene pre-Reid glacial limits was found in the study area; 2) placer potential was identified along the Reid glacial limit where a significant drainage diversion occurred for Grayling Creek; 3) widespread permafrost was encountered in the study area including near-continuous veneers of sheet-wash; and 4) a monitoring program was initiated at a recently active landslide which has potential to develop into a catastrophic failure that could damage the White River bridge on the Alaska Highway.