NTGS Researchers Publish Study on the Downstream Impacts of Permafrost Thaw

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Researchers at the Northwest Territories Geological Survey (NTGS) and NWT Centre for Geomatics (NWTCG) are studying the recent increase in landslides caused by permafrost thaw in northwestern Canada. 

The research team collaborated with university and community partners to show that increases in landslides caused by thawing permafrost over the last 20 years are transforming thousands of small headwater streams. The landslides release a large amount of thawed sediment which is transported downstream affecting aquatic environments. The study was recently published in The Cryosphere.

Lead by Dr Steve Kokelj, Permafrost Scientist at the NTGS, the research team first mapped lakes, streams and coastlines impacted by the landslides. The team then modelled the movement of sediment from the landslides downstream through the river systems to the ocean. 

Their findings show that a 1 million km2 Arctic drainage area of northwestern Canada is a hotspot of permafrost thaw where rivers will increasingly carry sediment downstream. The transported sediment will ultimately affect the water chemistry and quality. 

 

Thaw slumps and landslides located along the Willow River west of Aklavik (August 2020). Slope disturbances are directly affecting 116 km of the 861 km river channel.

 

By involving NWT Centre for Geomatics UAV expert Jurjen van der Sluijs, the team has been able to use high-resolution drone imagery to construct 3D models of landslides to estimate their growth over time. The amount of sediment displaced by the landslides can also be estimated. This has contributed new information on landscape change that contributes to permafrost monitoring in the Beaufort Delta region. 

The permafrost in this region contains a large amount of ice, which keeps the ground solid so long as it remains frozen. Warming temperatures and increasing intensity of rainfall are causing ground ice to melt, producing unstable ground and an increase in slope disturbances, including landslides known as thaw slumps. 

Thaw slumps are triggered when erosion causes ground ice to become exposed to solar energy.

As the ground ice melts, sediment and meltwater slide down from the headwall of the slump, forming a saturated slurry that may accumulate on the disturbed slope, or move downslope to form debris flows that may exceed one kilometre in length.

Single thaw slumps have been known to persist for decades, with the largest failures displacing millions of cubic metres of material. 

 

FM2 “mega slump” shown in September 2020. By 2018, the area of slump FM2 was an order of magnitude larger than the other disturbances on the Peel Plateau.

 

One thaw slump that the team is closely monitoring is known as FM2. Classified as a mega slump, FM2 is located in the Peel Plateau approximately 1 kilometre from the Dempster Highway.

Over the past 20 years, FM2 has displaced 6 million cubic metres of material – about four times the volume of the Rogers Centre in Toronto – leaving behind a debris flow measuring over 2 kilometres long. 

Thaw slumps and other slope disturbances caused by thawing permafrost can have significant downstream effects on landscapes and ecosystems.

Not only do they disturb existing vegetation and reshape slopes and valleys, but they also release a large amount of sediment and soluble materials into lakes and rivers, causing water colour and quality changes, contributing to coastal erosion, and posing risks to infrastructure and cultural sites. 

The research team is working to quantify the potential effects of these disturbances. As part of their study, the group developed models to estimate the volume of material that is released from thaw slumps.

They have also examined the stream networks to understand how the sediment could move through them in the years to come.

The research team’s map of stream systems across northwestern Canada affected by permafrost thaw is the first of its kind. According to the authors, the map is helping to visualize the scope and scale of potential downstream effects, as well as guiding future research activities.

 

The research team’s map of landslide density and accumulated effects is helping to visualize their scope and scale across northwestern Canada. 

 

The Willow River, which flows into the Peel Channel near Aklavik, is of particular interest to the research team. Between 2007-2009, an influx of material from upstream disturbances caused a segment of the river channel to be rerouted away from its previous path, leading to the rapid infilling of a 3.4 km2 lake. 

 

Landslides along the Willow River have released an influx of sediment into the stream network, causing the channel to be rerouted and Willow Lake (pictured in August 2020) to become infilled with sediment.

 

According to co-author and University of Alberta PhD candidate Sarah Shakil, sediment released from thawing permafrost can have numerous environmental consequences, including the release of CO2 into the atmosphere, an increase in the availability of nutrients such as phosphorus and nitrogen, and the release of methylmercury, a harmful toxin that can move through food webs. 

The study is also unique because it has been led by northern-based scientists, enabling a focus on northern concerns and strengthening relationships with land users, northern governments and Indigenous organizations. 

According to lead author Dr. Steven Kokelj, the need for northern permafrost science capacity was long overdue, and recent investments have already significantly improved collaborations to address thaw-driven landscape change. 

 

Other resources:

Thaw-driven mass wasting couples slopes with downstream systems, and effects propagate through Arctic drainage networks