Ground ice detection and implications for permafrost geomorphology

Most permafrost contains ground ice, often as pore ice or thin veins or lenses of ice. In certain circumstance, larger bodies of ice can form, such as ice wedges, or massive lenses up to tens of metres thick. These ice bodies can be quite pure and, on a volume basis, can occupy up to 97% of the subsurface. The location, type and quantity of this ice are important for several reasons. From a practical perspective, ground ice affects the thermal and physical properties of the ground, and can cause major landscape disturbances upon thawing. In addition, understanding its emplacement helps to explain landscape history. For instance, identifying buried glacier ice can help in explaining the glacial history of a region. A main objective of our research is to determine the areal and the stratigraphic distribution of ground ice. The goal is to identify where different ice types are likely to occur, and how much ice is present. Note that this is not the same as mapping the distribution of permafrost. Often it is possible to identify the presence of ice by its association with geomorphic features at the surface. For example, the thaw of massive ice can form a retrogressive thaw slump which leaves a distinct crescentic scar. Ice wedges will often have a trough at the surface, forming a polygonal net on the tundra, although these can sometimes be masked by vegetation cover. Pingoes are distinctive ice-cored hills (found mostly in the Mackenzie Delta). A number of other proxies can be used including marine terraces, peat plateaux, or involutions on upland surfaces such as those found near Tuktoyatuk. Subsurface investigations can help detect both the location and the amount of ground ice, either through direct methods such as coring and drilling, or through indirect methods such a geophysics. Surficial geology can also be used, as ground ice is often found in association with specific materials. When considering the thaw of permafrost, the primary area of concern is often the thawing of the ground ice and how it will be affected by warming at the surface. Thermal modeling is used to assess how quickly a change in surface temperature can propagate to the depth of the ice bodies. The ground thermal properties used in the modeling are often a function of the ground ice content in the upper layers, however, and if they cannot be measured directly, then values are estimated or extrapolated from sites with similar conditions. Also of interest, is how the thaw of ground ice changes the landscape. The most obvious changes are geomorphic - mass movements on slopes, or subsidence of the ground surface proportional to the loss of ice volume. These are the processes which can have serious implications for infrastructure. Knowledge of the geotechnical properties of the sediments is necessary for these types of investigations. Major changes to hydrological regimes are another consequence of ground ice thaw, either because of water accumulation or through the development of new drainage pathways. This, in turn, can affect vegetation. The thermal regime can be affected by water or snow accumulation in thermokarst depressions. Thawing ground ice can also change the geochemistry of water bodies by mobilizing salts, metals, organic carbon and sediment. Therefore, ice and enclosing sediments are typically sampled for geochemical analyses. Research activities include a project that is part of the Program on Energy Research and Development. It involves mapping the distribution of ice-rich permafrost around Parson's Lake north of Inuvik, at the site of a planned natural gas processing and distribution facility. The site was chosen because geotechnical data are available from a previous drilling program which make it a useful training site for calibrating techniques that combine several geophysical tools : GPR, resistivity, and conductivity. Stratigraphic maps of the subsurface can be produced from these data, providing two types of information: 1) the extent of massive ice bodies, and 2) changes in stratigraphic ice contents. Ice content data are used to parameterize thermal models and estimate how the ground ice will be affected by surface changes. Following calibration, the techniques can be applied to sites with little baseline information is available. This type of approach is also being used to detect ground ice at granular resources sites. The ground ice affects extraction activities because 1) its thaw can disrupt infrastructure, hydrology, etc., and 2) the volume it occupies can lead to an overestimate of the resources that are actually available. This knowledge will assist in developing regulatory policies for development sites. Another approach we use involves morphological mapping to quantify ground ice volumes at the landscape scale. Stratigraphic relationships between different ice types and the ice contents of each type are examined in order to assess the actual volume of ice in various types of terrain units. This information can then be applied to modelling the geomorphic changes that might be expected at the landscape scale as a result of climate warming, or the volume of material fluxes. The amount of sediment or contaminants is highly dependent on the volume of ground ice. So if ground ice accounts for 30% or 50% or 75% of soil volume, it has a major effect on sediment or contaminant budgets. This has implications for water geochemistry and ecology; it also affects coastal erosion rates, posing a threat to infrastructure, or increasing channel sedimentation and hazards to navigation. Current activities are centered in the Mackenzie Delta region. The Parson's Lake project, discussed above, is undertaken in conjunction with McGill University, Indian and Northern Affairs Canada (INAC), and industrial partners. Other work has involved mapping of ground ice in coastal areas to estimate organic carbon fluxes along the Yukon coast and collaboration with the GSC Atlantic to assess sediment transport in the Mackenzie Delta during spring break up, as well as the role of ground ice in coastal stability. A related activity involves assisting CCRS to ground truth and interpret their InSAR data, with regards to ground ice on Herschel Island. Ground ice and resulting coastal fluxes are also part of a new project in the Environmental Geoscience Program examining the mobilization of mercury in the Arctic. Others partners in this project are the Arctic Monitoring and Assessment Program (AMAP), INAC's Northern Contaminants program, University of Manitoba, and the Alfred Wegener Institute in Germany. At the international level, we are involved with the Arctic Coastal Dynamics project and AMAP in investigating fluxes of various sorts from eroding permafrost and developing a better understanding of the role of ground ice in controlling what occurs in the near offshore as well as the onshore zones. In the near future, with plans for an Inuvik-Tuktoyaktuk all-weather road, there will likely be a need for work related to terrain sensitivity of ice-rich terrain, and extraction of granular resources required for the project. In addition, the effect of ground ice on coastal erosion along the Yukon and NWT is of interest to Parks Canada's because of heritage sites that are threatened by erosion. The use of integrated geophysical methods for assessing ground ice distribution and stratigraphy still requires much ground truthing. The relationship between ground ice and sediment transport in coastal areas needs to be better developed. This is especially important, given the effects of a warming climate, including changing air and water temperatures, rising sea level, increased storminess and decreasing sea ice cover. The MORSE Arctic Coastal Initiative (CSA and ESA sponsored) outlined a number of EO requirements and information needed from a range of users.