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.

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.

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.

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 production of acid rock drainage (ARD) from mine tailings is a significant environmental concern at various abandoned mine sites in Yukon. Leachate with low pH and high dissolved metals concentrations deriving from mine tailings impoundment areas can negatively impact various groundwater and surface water resources. The presence of both oxygen and water is required for ARD to develop. Therefore, the reduction of the oxygen and water sources from the mine tailings will limit ARD production. This is the basis of reclamation of the Arctic Gold and Silver (AGS) Tailings Site near Carcross, Yukon using a lowpermeability tailings cover which acts as an oxygen and water infiltration barrier. ARD processes have resulted in a significant contamination of the groundwater beneath the tailings impoundment at the AGS site with multiple dissolved metals showing elevated concentrations. The use of a low permeability cover to reduce ARD such as that used at the AGS site is one of the first such reclamation applications in Yukon. EBA Engineering Consultants Ltd. and partners initiated a performance assessment of the low permeability cover system in the fall of 2000 and continued the monitoring in 2001 as part of Mining Environment Research Group (MERG) funded studies. The results of these assessments suggested that the low-permeability cover functions as an oxygen and infiltration barrier; however, the limited data and short period of monitoring precluded any prediction of the long-term performance of the tailings cover. Further monitoring was recommended.

The production of acid rock drainage (ARD) from mine tailings is a significant environmental concern at various abandoned mine sites in Yukon. Leachate with low pH and high dissolved metals concentrations deriving from mine tailings impoundment areas can negatively impact various groundwater and surface water resources. The presence of both oxygen and water is required for ARD to develop. Therefore, the reduction of the oxygen source and the water source from the mine tailings through the use of a low permeability cover (which acts as an oxygen/infiltration barrier) will limit ARD production. This is the basis of the design and recent reclamation (1998-99) of the Arctic Gold and Silver Tailings Site in Carcross, Yukon that EBA has been involved with in association with PWGSC.

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.

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)

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)

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.