ABSTRACT: Landslide inventory along a pipeline corridor in the Mackenzie Valley, Northwest Territories.

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A regional landslide mapping project was initiated by Natural Resources Canada to develop a synthesis of the types, regional distribution, and controlling factors of landslides in the Mackenzie Valley through a compilation of existing and new spatial data. The Mackenzie Valley study area encompasses a corridor extending to 20 km on either side of the Inuvik - Tulita section of a newly proposed pipeline route, with a length of 540 km and an area of 24,000 km2. This also includes the Ramparts and the Thunder River regions, both known for widespread landsliding. The study area is covered by unconsolidated sediments (99%), which are dominated by morainal (60%), lacustrine (18%), and alluvial (10%) deposits. Three types of permafrost were mapped: i) continuous, ii) extensive discontinuous, and iii) intermediate discontinuous. Using classical air photo interpretation techniques, a preliminary inventory of 1,807 landslides and other natural terrain hazard features has been identified using 665 colour air photos (1:30,000 scale) acquired in 2004. The digital air photos that contained at least one landslide were then orthorectified. The landslide limits were digitized from the orthophotos and catalogued in the Mackenzie Valley landslide Spatial Database. For each landslide feature, the following attributes were recorded: unique identifier, landslide type, size (area), location, morphological parameters, relative age, activity, material, flight line, air photo number, and topographic map sheet number. A collection of several hundred photographs of landslides, taken while carrying out field surveys in 2005 and 2006, completes the database. Using the spatial database attributes, landslide mapping and statistical analyses were performed to characterise the landslide distribution. The results indicate an average density of one landslide per 5 km2 and show that the dominant landslide types are retrogressive thaw flows (28%) and active layer detachments (25%). Rock falls (10%), debris flows (10%), earth slides (9%), surficial landslides (6%), and retrogressive thaw slides (5%) are lesser represented. About 46% of all landslides took place in morainal deposits, 19% in lacustrine sediments, 14% in bedrock, and 13% in glaciofluvial sediments. The relative age of landslides was estimated based on tone, texture, and vegetation re-growth attributes, where 39% were classified old (>50 years old), 39% intermediate (10-50 years old), and 22% recent (<10 years old).

Bibliography of Canadian Geomorphology