|Title||Thaw depth monitoring in the Mackenzie Valley, Northwest Territories|
|Author||Smith, S L; Duchesne, C|
|Source||2017 Yellowknife Geoscience Forum, abstract and summary volume; Northwest Territories Geological Survey, Yellowknife Geoscience Forum Abstracts Volume 2017, 2017 p. 75 (Open Access)|
|Links||Online - En direct (complete
volume - volume complet, 1.69 MB)|
|Alt Series||Natural Resources Canada, Contribution Series 20180068|
|Publisher||Northwest Territories Geological Survey|
|Meeting||45th Annual Yellowknife Geoscience Forum; Yellowknife, NT; CA; November 14-16, 2017|
|Media||paper; on-line; digital|
|NTS||95H; 95I; 95J; 95N; 95O; 96C; 96D; 96E; 96F; 96L; 106I; 106J; 106N; 106O; 106P; 107B; 107C|
|Lat/Long WENS||-136.0000 -120.0000 70.0000 61.0000|
|Subjects||environmental geology; surficial geology/geomorphology; Nature and Environment; permafrost; ground ice; climate; in-field instrumentation; permafrost thaw; climate change; monitoring; thaw depth; active
layer thickness; thaw penetration; landscape stability; ground settlement; thaw tubes|
|Abstract||In permafrost regions, increases in thaw depth in response to a warming climate have considerable implications for landscape stability, infrastructure integrity, drainage and ecosystems. In ice-rich
terrain, increases in thaw depth can result in significant ground settlement due to melting of excess ice. This leads to a reduction of the thawed layer so that over time, active layer thickness (i.e. thickness of the seasonally thawed layer) may
change very little even though the lower boundary of the active layer continues to progress deeper into the ground.|
Mechanical probing is often used to monitor active layer thickness but this method does not consider changes in surface elevation
over time and therefore does not provide an accurate picture of the loss of frozen ground that may occur in response to a warming climate. Thaw tubes however, do allow tracking of both thaw penetration, relative to a fixed datum, and thaw settlement.
Thaw tubes have been used, by the Geological Survey of Canada, throughout the Mackenzie Valley since the early 1990s as part of a permafrost monitoring program. Records up to 25 years long exist for over 40 sites.
Analysis of thaw depths indicates
that at sites located within ice-rich terrain, increases in thaw penetration (measured relative to original ground surface) over the last two decades can be as much as double the increase in active layer thickness over the same period. For example,
data from two sites in the Central Mackenzie Valley indicate that between 1993 and 2014 thaw penetration increased by 21-29 cm, a process which was accompanied by 12-15 cm of settlement. The active layer thickness over this period, however, only
increased by 10-12 cm. The loss of frozen ground over time, may therefore be considerably more than that indicated by the change in active layer thickness alone.
Data analysis from the active layer monitoring network help describe relations
between thaw penetration, settlement and ground conditions. These results can advance our understanding of changes in regional permafrost conditions. They can also contribute to better representation of active layer processes in models and improved
prediction of future permafrost conditions.
|Summary||(Plain Language Summary, not published)|
In permafrost regions, increases in thaw depth in response to a warming climate has considerable implications for landscape stability, infrastructure
integrity, drainage and ecosystems. Information will be presented on thaw depth acquired from an extensive network of instrumented sites in the Mackenzie Valley NWT. Increases in summer thaw penetration over time will be summarized along with
implications including surface settlement and permafrost loss. The information provided advances our understanding of changes in regional permafrost conditions and can also contribute to improved models for prediction of future permafrost