Satellite images are revealing how the landscape of Banks Island in the frozen north of Canada is being reshaped by global warming-triggered land slumps. The number of slumps, which normally starts with a land slide that then continues to move much more slowly over a period of years, has rapidly increased from 63 in 1984 to more than 4000 in 2013.
“It is clear that something really dramatic is happening,” says Antoni Lewkowicz of the University of Ottawa in Canada.
The local Inuvialuit people say it is becoming harder to move around the island, and they can no longer drink from many streams because they are full of mud. “If any of us had the equivalent of our backyard being eaten up and turned into a mudpit, I think we’d all be quite upset about it,” says Lewkowicz .
Around the southern edges of the Arctic, the melting of permafrost is already causing huge problems as buildings tilt and roads buckle. What’s worrying about the land slumps is that they are occurring even in areas in the far north, such as Banks Island, where the permafrost was not thought to be at risk.
Fortunately only parts of the Arctic where the permafrost contains a lot of ice are vulnerable to this kind of land slump. A survey last year of a much bigger area of the Arctic found that slumps were “abundant but localised”.
Slumps from space
Lewkowicz first went to Bank Island in the 1980s to study retrogressive thaw slumps, as they are known. Now his team has used satellite images from the Google Earth Engine Timelapse feature to study them from space.
Despite their name, it was thought that thaw slumps are triggered by processes such as erosion by waves or rivers. But Lewkowicz found almost all the slumps first formed when particularly warm summers cause deeper thawing of the land surface than usual.
If there is lots of ice near the top of the permafrost, the soil becomes sodden and turns into mud. In places, it can just slide away — and this is just the start of the process.
Around the edges of the initial slump, once-buried permafrost is left exposed to the air. This leads to further slumps carving away a widening-circle of land every summer even if those summers are not particularly hot. On average, retrogressive thaw slumps spread by around 10 metres a year for 30 years, says Lewkowicz.
You can see slumps spreading in the video below. The lake changes colour as it fills with sediment.
The 70,000 musk oxen on Banks Island can probably cope with the mud. Lewkowicz thinks life in lakes and rivers is probably being hardest hit by the slumps, but as no one has ever studied them we simply don’t know.
What is clear is that this is just the start. Even in the very unlikely event that we manage to limit warming to 2°C, computer models suggest that by 2075 more than 10,000 new slumps will be forming on Banks Island each decade.
The organic matter from the slumps will decompose and release methane or carbon dioxide, adding to the warming. “It’s not trivial but it’s not catastrophic either,” Lewkowicz says.
Banks Island is 70,000 square kilometres in area – the same as the Republic of Ireland – but is home to just 112 people. The study findings match perfectly with what they have been telling researchers, says Lewkowicz.
Globally rain-triggered landslides kill several thousand people each year. Their number may be increasing as warming leads to more intense rainfall events, but other factors such as rising populations and deforestation play a part too.
Journal reference: Nature Communications, DOI: 10.1038/s41467-019-09314-7
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