Scientists Identify Possible Cause of Massive Northwest Territories Landslides
A 2018 landslide in Canada’s Northwest Territories moved 18 million cubic meters of earth and blocked the Redstone River. Researchers say thawing beneath permafrost may help explain how the frozen ground broke free, and identified more than 150 other slides that may fit the same category.
A 2018 landslide in Canada’s Northwest Territories sent roughly seven Great Pyramids’ worth of earth downhill, blocking the Redstone River as much of the material remained frozen.
The slide moved 23.5 million cubic yards (18 million cubic meters) of earth. Researchers have identified a possible explanation: water may have thawed the underside of the permafrost layer, allowing frozen ground to break free.
The research, published in Geophysical Research Letters in September, describes a previously unrecognized category called permafrost detachment slides. Scientists examined two enormous slides in the region: the 2018 event and a 2017 slide that displaced 5.9 million cubic yards (4.5 million cubic meters).
How can a landslide move frozen ground?
Both slides began along relatively flat surfaces about 66 feet (20 meters) underground, at the base of the permafrost layer. Satellite observations showed gradual movement at both locations over decades, with ground shifting yards (meters) each year.
Joseph Young, a permafrost geologist then based at the University of Alberta, visited one site in 2019. He found large blocks of frozen ground that appeared to have traveled hundreds of yards (hundreds of meters), prompting an investigation.
Researchers say wildfires or unusually hot summers can warm and weaken the surface, allowing tension cracks to form as the ground creeps. Water may then pass through the cracks and melt permafrost from below, helping the frozen layer detach.
To investigate the process, Young and his colleagues monitored underground temperatures from 2020 to 2022, comparing undisturbed forest with areas burned by wildfires roughly a quarter-century earlier. They used the measurements in computer simulations to estimate how ground conditions could change in the decades after a fire. The results supported a connection between fire, surface weakening, water infiltration and thaw beneath the frozen layer.
Satellite observations identified more than 150 additional slides in the region that may fit the category, Young said. The process could occur wherever relatively thin, warm permafrost encounters rapid warming.
Dmitry Nicolsky, a University of Alaska Fairbanks geophysicist who was not involved in the study, said subsurface conditions matter. “We don't know how [the ground] will move — it might go slowly or it might go catastrophically,” he said.
Young described the failures as part of a wider pattern of permafrost thaw. “This is a direct reality of a changing climate,” he said.
