| Titre | Influence of terrain and highway construction on thermokarst distribution, North Slave Region, Northwest Territories, Canada |
| Auteur | Morse, P D; Wolfe, S A; McWade, T L |
| Source | Northwest Territories Geological Survey, Yellowknife Geoscience Forum Abstract and Summary Volume 2017, 2017 p. 105-106 (Accès ouvert) |
| Liens | Online - En ligne (complete
volume - volume complet, pdf, 1.69 MB)
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| Année | 2017 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20170265 |
| Éditeur | Commission géologique des Territoires du Nord-Ouest |
| Réunion | 2017 Yellowknife Geoscience Forum; Yellowknife, NT; CA; Novembre 14-16, 2017 |
| Document | publication en série |
| Lang. | anglais |
| Media | papier; en ligne; numérique |
| Formats | pdf (Adobe® Reader®) |
| Province | Territoires du Nord-Ouest |
| SNRC | 85J; 85K |
| Région | Tlicho Region; North Slave Region; Behchokö; Yellowknife; Grand lac des Esclaves |
| Lat/Long OENS | -118.0000 -114.0000 63.0000 62.0000 |
| Sujets | pergélisol; glace fossile; caractéristiques périglaciaires; thermokarst; affaissement; antecedents glaciaires; lacs glaciaires; emersion; télédétection; dépôts glaciaires; silts; argiles; exploitation
minière; ballastières; eaux de surface; tourbières; tourbières minérotrophes; Holocène; Lac glaciaire de McConnell; risque pour l'environnement; infrastructure; construction routière; sédiments glaciolacustres; sédiments fluvioglaciaires; buttes
cryogènes; altitude; couverture du sol; forêt; géologie de l'environnement; géologie des dépôts meubles/géomorphologie; Transport; géophysique; Phanérozoïque; Cénozoïque; Quaternaire |
| Programme | Géosciences de changements climatiques, Pergélisols |
| Diffusé | 2017 11 01 |
| Résumé | (disponible en anglais seulement)
Permafrost degradation is occurring widely in the circumpolar north and is expected to have broad-reaching effects on the land and its inhabitants. However,
there is little quantitative information on thermokarst distribution and development in northern Canada, including southern North Slave, NT. Permafrost in the region is presently degrading, and modelling suggests the discontinuous permafrost extent
will decline significantly. Differential thaw subsidence has already occurred along Highway 3, affecting drivability and maintenance costs on this important transportation artery. The objective of this study was to quantify thermokarst development in
order to evaluate the dominant terrain controls, and the influence of Highway 3, on the distribution of thermokarst. We mapped the location and size of thermokarst ponding (a change from forest cover to water) in a 1430 km2 study area by comparing
historic and modern remotely sensed imagery from 1945, 1961, and 2005.
Permafrost in the region developed in a time-transgressive manner during Holocene lake-level recession, from glacial Lake McConnell to the present-day level of Great Slave Lake
(5 mm·a-1 over the last 8000 years). The past inundation has left uplands of extensive wave-washed bedrock outcrops with depressions filled with glaciolacustrine (GL) and glaciofluvial sediments. In contrast, GL deposits cover more of the landscape,
nearly 70 % of the exposed surface, at lower elevation in Great Slave Lowlands. Ground ice accumulation accompanied permafrost aggradation into the fine-grained sediments, and is evident on the landscape in the form of widespread
lithalsas.
Highway 3 was constructed during the mid-1960s and preferentially aligned to cross terrain underlain by fine-grained sediments to avoid bedrock and waterbodies. Local silt and clay used to construct the road embankment was sourced from
shallow borrow pits developed along the right-of-way. Following construction, many borrow pits developed into ponds. Major highway realignments between 1999 and 2006 maximized bedrock traverses to reduce the construction on thaw-sensitive permafrost
and limit embankment settlement.
Thermokarst ponding is widespread in the study area (n = 3138). The individual area of most new ponding is typically small (< 5000 m2) but ranges up to 45 000 m2. Thermokarst development is dominantly constrained
within GL deposits, and decreases with elevation. Highway construction has substantially affected thermokarst development. Compared to undisturbed GL deposits, ponding density is an order of magnitude greater within 200 m of Highway 3, where more
than 95 % of ponding has developed since 1961 and about half of the borrow pits have developed into thermokarst ponds.
Thermokarst is likely widespread throughout the region as GL deposits are extensive. The transition of approximately 3.57 km2 of
land cover from forested permafrost terrain to water bodies differs from the low subarctic where permafrost peatlands degrade to fens. Reduced thermokarst ponding at higher elevation may relate to the limited GL sediment cover, but also to greater
time for past thermokarst development due to earlier emergence following lake-level recession. Regardless, thermokarst development will likely continue in low-lying forested GL deposits that should be avoided by new infrastructure
construction. |
| Sommaire | (Résumé en langage clair et simple, non publié)
La dégradation du pergélisol (thermokarst), observée dans le nord du pays, devrait avoir des effets à grande échelle sur le territoire et ses
habitants. Il existe peu de données pour une grande partie du nord du Canada, y compris le sud de la région du North Slave, au TNO. Nous avons cartographié l'emplacement et la taille de formations thermokarstiques (changement de couverture forestière
à étang) dans une zone d'étude de près de 1 430 km2, en comparant des ensembles de données de télédétection historiques et modernes disponibles pour 1945, 1961 et 2005. Nous avons évalué les formations thermokarstiques et l'influence potentielle de
la construction d'une autoroute. La formation de dépôts thermokarstiques (n = 3138) est principalement restreinte aux dépôts de limon et d'argile et la formation d'étangs diminue avec l'altitude. La construction de routes a considérablement affecté
le développement de thermokarst. La densité des étang est 10 fois plus grande à proximité de la route 3 que sur un terrain non perturbé. Plus de 95% des étangs situés à moins de 200 m de l'autoroute se sont développés depuis 1961.
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| GEOSCAN ID | 306193 |
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