New study delved into two significant landslides that occurred nearly ten years ago in the Mackenzie River basin. The incidents, known as permafrost detachment slides, took place on the Johnson River in 2017 and the Redstone River in 2018. These events stand out from typical permafrost-related landslides caused by thawing. Joseph Young, a former University of Alberta PhD student and the lead author of a recent study published in Geophysical Research Letters, highlighted the distinction.
In permafrost areas, failures usually start from the top due to warming temperatures and increased precipitation, leading to gradual landslides over decades. However, permafrost detachment slides occur differently, with the permafrost failing about 20 meters below the surface, causing a rapid and abrupt upward failure instead of the typical downward progression.
These detachment slides are described as extensive and swift, capable of moving vast amounts of material in days that would typically take decades for standard permafrost failures to achieve. The Redstone River landslide in August 2018 displaced around 4.5 million cubic meters of earth, while the Johnson River slide in August 2017 moved approximately 18 million cubic meters, equivalent to filling about 7,200 Olympic swimming pools.
Eric McLeod, who witnessed the Johnson River slide from the air, observed the landscape changes during his flights over the area in subsequent years. He noted that the land appeared to have “stretch marks” as a result of the sudden movements, unlike gradual erosion he had seen before. The wildfires in 1995 triggered the events that led to these large-scale landslides, according to Young and co-author Steve Kokelj from the Northwest Territories Geological Survey.
The wildfires in 1995 eliminated organic material, impacting the top layer of permafrost. Over the following 15 to 20 years, disturbances occurred due to the fire’s effects, warming the permafrost and compounded by climate change. Young and Kokelj mentioned that there are warning signs before a permafrost detachment slide occurs, allowing for predictions before such events unfold gradually over about two decades following a fire.