During the spring of 1978, 12 holes were hydraulically jet-drilled from the sea-ice to maximum depths of 61m beneath the Beaufort Sea, The holes, located in a line across the Delta Front north of Richards Island: were instrumented with temperature cables and monitored as the thermal disturbance due to the jetting dissipated, Much of the sea-bottom material encountered was marginally ice-bonded and permafrost occurred at all sites, Temperatures in the sea-bottom were below O°C averaging around -1,5° to -1.0° C, Temperature gradients were near isothermal and are probably indicative of relict degrading permafrost, The shallow lithology interpreted from the drilling logs revealed definite changes in material type and thickness occurring across the Delta Front from Mackenzie Canyon to Kugmallit Bay. Water temperature and salinity profiles at the drill sites reflected the influence of the warmer and fresher Mackenzie River waters flowing into Mackenzie Bay and Kugmallit Bay.
Permafrost has received much attention recently because surface temperatures are rising in most permafrost areas of the Earth, bringing permafrost to the edge of widespread thawing and degradation. The thawing of permafrost that already occurs at the southern limits of the permafrost zone can generate dramatic changes in ecosystems and in infrastructure performance. In this article, we describe an emerging system for comprehensive monitoring of permafrost temperatures, a system which is needed for timely detection of worldwide changes in permafrost stability, and for predictions of negative consequences of permafrost degradation. Permafrost is rock, sediment, or any other Earth material with a temperature that remains below 0°C for two or more years. Permafrost zones occupy up to 24% of the exposed land area of the Northern Hemisphere (Figure 1) [ Zhang et al. , 2000]. Permafrost ranges from very cold (temperatures of −10°C and lower) and very thick (more than 500 m and as much as 1400 m) in the Arctic, to warm (within 1 or 2° of the melting point) and thin (several meters or less in thickness) in the sub‐Arctic.
The temperature in the ground changes according to daily or longer temperature cycles in the air. The amount of ground temperature change also diminishes rapidly with depth. Temperatures to a depth of 20 m, the approximate depth to which the yearly temperature cycle penetrates, are presented for various environments in the Mackenzie valley. As a rough guideline, average ground temperatures are about 4°C warmer than mean annual air temperatures. This difference depends mainly on the insulating affect of vegetation and snow and changes in the moisture content of the active layer. Smaller differences may result in peatlands where summer drying of organic soils enhances their insulating capacity. Even without a change in climate, disturbance at the ground surface will alter the ground thermal regime. Examples from the Norman Wells to Zama, Alberta oil pipeline show warming and ground subsidence associated with the clearing of the pipeline right-of-way.
The Permafrost Research Section of the Geological Survey of Canada, Department of Energy, Mines and Resources, cooperates with the Department of Indian and Northern Affairs and Interprovincial Pipe Line Ltd. (IPL), in a long term ground thermal regime monitoring program along the Norman Wells to Zama pipeline. The program is designed to examine the effects of the construction and operation of the Norman Wells pipeline on permafrost and terrain conditions and to evaluate the approaches used to minimize terrain disturbance. The program focuses on thirteen main monitoring sites representing a cross section of the terrain conditions encountered by the buried, "ambient" temperature, oil pipeline as it traverses the discontinuous permafrost zone. These monitoring sites established during the construction period are instrumented with multi thermistor cab les to measure pipe temperatures and ground temperatures both on and off the right-of-way. Since pipeline operation began in April 1985, additional cables have been installed to instrument 1) five thaw settlement sites drilled by IPL in 1986, 2) additional boreholes drilled at existing government monitoring locations, and 3) deep (>90 m) boreholes drilled for climate change studies along the pipeline corridor. This report is a collection of the data gathered in 1987 from all cables at the government monitoring sites (in total over 145 cables). Data are presented both graphically and in tabular form.
The surficial geology of the Mackenzie valley and adjacent areas is presented in 1:1 000 000 scale compilation maps and is accompanied by geotechnical data from 56 boreholes chosen to represent typical stratigraphy of each major geological unit at several locations along the valley. For each of the representative boreholes, the potential for settlement of the ground surface as frozen ground thaws is determined, based on the thaw strain calculated for each soil layer of the borehole. Those geological materials most sensitive to thaw settlement are lacustrine and morainal, ice-rich, fine-grained sediments, and also the ice-rich and potentially highly compressible peat bogs. Much of the Mackenzie region is underlain by these materials; thus extensive terrain is susceptible to the impact of warming climatic conditions.
Regional studies show that permafrost will disappear partly or completely over large areas of the north should predicted climate change occur. Much of the infrastructure in northern communities relies on the properties of frozen materials for stability. Ground warming could degrade the performance of existing structures. The Geological Survey of Canada is initiating an assessment of infrastructure needs in the north, by examining sensitivity to impacts of permafrost degradation under climate warming, using a community-level approach in the Mackenzie valley. Over the last century, this area has undergone the most warming in Canada and mean annual air temperatures are predicted increase up to 4° or 5°C in the next century. Preliminary results are presented of the pilot study at Norman Wells, Northwest Territories, where surficial geology, permafrost, and geotechnical conditions are described, and performance and sensitivity of infrastructure are examined.
The Norman Wells to Zama pipeline, located in northwestern Canada, is the first buried oil pipeline in the permafrost zone in Canada. During its construction in 1984-1985, the Canadian government and Enbridge Pipelines (NW) Inc. (formerly Interprovincial Pipe Line Ltd.) collaborated in the establishment of a permafrost thermal monitoring program consisting of more than 20 long-term thermal monitoring sites along the pipeline corridor. This contributed to a larger Permafrost and Terrain Research and Monitoring Program established to improve impact evaluation and mitigation on the Norman Wells and future pipelines. The thermal monitoring study was designed to investigate the impact of the pipeline construction and operation on permafrost and terrain conditions and to evaluate the approaches used to minimize terrain disturbance. The project focuses on 23 main monitoring sites (referred to as thermal fences) in representative terrain conditions encountered as the pipeline traverses the discontinuous permafrost zone. Multi-thermistor cables were installed both on and off the pipeline right-of-way to measure temperatures to depths of up to 20 metres. Observations of thaw depth and thaw settlement are also recorded in addition to ground temperatures. This CD presents the thermal data collected between 1984 and 2001 as well as a software program that will provide access to the data. Case histories for each monitoring site are also presented which include summaries of the trends in thermal conditions, thaw depth and thaw settlement. A synthesis is also presented which summarizes the trends in these conditions for each major terrain group.
