| Title | Influence of terrain and highway construction on thermokarst distribution, North Slave Region, Northwest Territories, Canada |
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| Author | 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  Open Access |
| Links | Online - En ligne (complete
volume - volume complet, pdf, 1.69 MB)
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| Image |  |
| Year | 2017 |
| Alt Series | Natural Resources Canada, Contribution Series 20170265 |
| Publisher | Northwest Territories Geological Survey |
| Meeting | 2017 Yellowknife Geoscience Forum; Yellowknife, NT; CA; November 14-16, 2017 |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf (Adobe® Reader®) |
| Province | Northwest Territories |
| NTS | 85J; 85K |
| Area | Tlicho Region; North Slave Region; Behchokö; Yellowknife; Great Slave Lake |
| Lat/Long WENS | -118.0000 -114.0000 63.0000 62.0000 |
| Subjects | environmental geology; surficial geology/geomorphology; Transport; geophysics; permafrost; ground ice; periglacial features; thermokarst; subsidence; glacial history; glacial lakes; emergence; remote
sensing; glacial deposits; silts; clays; mining; borrow pits; surface waters; peatlands; fens; Holocene; Glacial Lake McConnell; Great Slave Lowlands; Environmental hazards; Infrastructures; Road construction; glaciolacustrine sediments;
glaciofluvial sediments; lithalsas; elevations; Land cover; Forests; Phanerozoic; Cenozoic; Quaternary |
| Program | Climate Change
Geoscience Permafrost |
| Released | 2017 11 01 |
| Abstract | 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. |
| Summary | (Plain Language Summary, not published)
Permafrost degradation (thermokarst), observed throughout the north, is expected to have broad reaching effects on the land and its people. There is
little data for much of Northern Canada, including southern North Slave, NT. We mapped the location and size of thermokarst ponding (a change from forest cover to water) in a nearly 1430 km2 study area, comparing historic and modern remotely sensed
data sets available from 1945, 1961, and 2005. We evaluated the dominant terrain controls on thermokarst distribution and the potential influence of highway construction. Widespread thermokarst ponding (n = 3138) is dominantly constrained to silt and
clay deposits and ponding decreases with increased elevation. Highway construction has substantially affected thermokarst development. Ponding density is 10 times greater in the vicinity of Highway 3 than within undisturbed terrain. More than 95 % of
ponding within 200 m of the highway has developed since 1961. |
| GEOSCAN ID | 306193 |
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