|Titre||Impact of climate change on slope stability in permafrost regions|
|Auteur||Wang, B; Lesage, K|
|Source||8th International Symposium on Cold region development, SCORD 2007, Extended abstracts; 2007 p. 97|
|Séries alt.||Secteur des sciences de la Terre, Contribution externe 20060373|
|Réunion||8th International Symposium on Cold region development (SCORD); Tampere; FI; Septembre 25-27, 2007|
|Province||Territoires du Nord-Ouest|
|SNRC||106M/09; 106M/16; 106N/09; 106N/10; 106N/11; 106N/12; 106N/13; 106N/14; 106N/15; 106N/16; 106O/11; 106O/12; 106O/13; 106O/14; 107A/04; 107A/05; 107A/12; 107A/13; 107B/01; 107B/02; 107B/03; 107B/06; 107B/07;
107B/08; 107B/09; 107B/10; 107B/11; 107B/14; 107B/15; 107B/16; 107C/01; 107C/02; 107C/03; 107C/06; 107C/07; 107C/08; 107D/04; 107D/05|
|Région||Mackenzie Valley; Fleuve Mackenzie|
|Lat/Long OENS||-134.4500 -131.1000 69.3167 67.5167|
|Sujets||dépôts de pentes; glissements de pentes; stabilité des pentes; analyses de la stabilité des pentes; pergélisol; études pédologiques; propriétés du sol; levés pédologiques; dépôts de glissement de terrain;
glissements de terrain; températures au sol; analyses thermiques; conductivité thermique; Changement climatique; géologie des dépôts meubles/géomorphologie; géologie de l'ingénieur; pédologie; Nature et environnement|
|Résumé||(disponible en anglais seulement)|
This paper presents a study on the impact of climate change on stability of slopes in fine-grained permafrost soils. Landslides in permafrost soils are common
in the Mackenzie valley, Canada and other arctic regions. They occur every year and most of them remain active for years. Those landslides are undoubtedly related to ground thermal condition changes. The fine-grained permafrost soils are usually
ice-rich. Surface active layer may displace if the underlying permafrost soil thaws and generates an excessive amount of water. The failure may continue after the underlying permafrost is exposed to the atmosphere resulting in the so called
solifluction. There is
a concern that global warming may change the ground thermal regime and consequently trigger more landslides. A study has therefore been carried out to assess this situation.
Numerical modelling studies were carried out
to investigate thermal condition changes in typical fine-grained permafrost soils in response to climate change. A two dimensional finite element model was used for this study. The model adopted the typical soil stratigraphy observed from the
Mackenzie valley. Daily climate data recorded from a local weather station in the Mackenzie valley from 1958 to 2005 was used for the analysis. Four climate conditions were assumed for the numerical model studies: (1) the coldest year (1974), (2) the
average year (1992), (3) the warmest year (1998), and (4) the "global warming" case. The actual daily weather records were used as input for the first three cases. A conservative assumption was made for the "global warming" case. It was indicated
from the literature that global average near-surface temperature increased by approximately 0.60 ± 0.2°C over 133 years, from 1861 to 1994. The most recent report by the United Nations Intergovernmental Panel on Climate Change (IPCC) in February 2007
referred to sources indicating a projection of 0.2ºC warming per decade for the next two decades. Using this information, a daily temperature increase of 0.6ºC from the warmest year data was assumed for the "global warming" model.
results were evaluated in conjunction with field observations at various landslide sites in the Mackenzie valley region. The numerical model results indicate that the maximum thaw depths ranged from 1.26 m to 1.56 m from the coldest case to the
warmest case. This is consistent with the field observations. Furthermore, the "global warming" model indicated only 0.01 m increase of thaw depth from the warmest case scenario.
Other studies reported by the authors of this paper confirmed that
there is a transient layer between the surface active layer (undergoing annual freeze-thaw cycles) and the permafrost. The moisture content of the transient layer is higher than that of the active layer and lower than that of the icerich permafrost
below. The transient layer acts as a critical buffer zone. If thawing penetrates through this zone and reaches the ice-rich layer, a significant amount of pore water would be released from the melting ice. This would reduce the shear strength of the
soil significantly and induce active layer sliding if the excessive pore water does not have a chance to dissipate. The impact of global warming on such type of landslides was discussed around this focal point.
The model results indicated a
transient zone of about 7 cm to 15 cm thick, which is consistent with the field observations. It is also consistent with those reported in the literature. The transient layer was created by the annual climate fluctuations. A majority of the slopes in
the region remain stable in spite of the extreme conditions they have experienced. This phenomenon indicates that the shear strength of the material at the bottom of the transient zone was not mobilized in the extreme weather years. The transient
zone and its buffering effect are continuously reconditioned by the annual climate variations. The relatively small increase of air temperature associated with global
warming and its very gradual nature would be reflected in the reconditioning
process of the transient zone. In other words, global warming would not cause more severe damage to the slopes than what the drastic climate change does from year to year.