Arctic ground can slide off whole as thin permafrost warms from below

Researchers identify a new landslide type in northern Canada in which an entire permafrost layer detaches, with 150 more suspected sites nearby.

Researchers have described a new class of catastrophic landslide, which they call a permafrost detachment slide. The findings are in Geophysical Research Letters, with Joseph Young as lead author. The two examples they studied are in Canada's Northwest Territories. A 2018 slide moved 18 million cubic meters of earth, about seven Great Pyramids of Giza by volume. It dammed the Redstone River in the Mackenzie Valley and created a lake 3.5 kilometers long. A 2017 slide moved 4.5 million cubic meters.

Both began on flat sliding surfaces about 20 meters down, at the base of the permafrost layer. Satellite data showed the ground at both sites had crept several meters a year for decades. Instruments recorded ground temperature from 2020 to 2022 at undisturbed forest sites and at sites burned by wildfire about 25 years earlier. Simulations built on that data suggest wildfire and extreme summer heat can warm and weaken the frozen surface, opening tension cracks. Water entering the cracks may reach beneath the permafrost, thaw it from below, and let the whole layer detach. Blocks of still-frozen ground appear to have travelled hundreds of meters at some sites.

This matters for shelter, security and the commons because it adds a hazard that is hard to see coming. The ground can creep for decades and then fail all at once, and a slide can also dam a river and flood land upstream. Anyone building or maintaining homes, roads and pipelines on Arctic permafrost now has a further risk to survey, monitor and insure against, which raises the cost of keeping those places safe.

Young says more than 150 other slides in the region, identified by satellite, may be of the same type. That is a possibility, not a confirmation. The wildfire-to-detachment chain is a hypothesis supported by simulations and field data, and the instruments ran only three years, so the simulations extrapolate to decades. The process may occur wherever permafrost is relatively thin and warm and a rapid warming event hits. Dmitry Nicolsky of the University of Alaska Fairbanks, who was not part of the study, says subsurface conditions need more study because ground may move slowly or catastrophically. Watch for field surveys of those suspected sites.

Source: Science News