What caused a stream of gooey, earthen debris to ooze through an empty field? Experts aren’t quite sure.
Video recently went viral on Chinese social media sites Weibo and WeChat showing a river of mud and grass moving through what social media users recognized as the Dimye village on the Qinghai-Tibet Plateau on September 7.
Unlike some landslides that can be quick and sudden, this moving mound is an earthflow, a type of landslide that generally oozes.
“It’s a slow, unstoppable force, but it’s not immediately going to kill anybody,” said landslide researcher Mika McKinnon.
According to local media, there were no fatalities or injuries from the September 7 flow, but one family’s ranch, seen in the video, was lost along with their car.
What Caused It?
Since the video began circulating on international social media accounts, many have speculated that the flow was caused by the melting of permafrost, or soil that’s normally frozen year-round. This kind of melting and the oddly pockmarked landforms that it creates are known as thermokarst.
Permafrost plays an important role in cold environments by keeping the overlying layer of soil in place and serving as the foundation on top of which trees and plants grow.
This permanently frozen ground covers about 24 percent of land in the Northern Hemisphere, according to figures on the meteorology site Weather Underground. The International Panel on Climate Change estimates that somewhere around the middle of the 21st century, nearly 20 to 35 percent of it could be gone.
This thawing could make the terrain more dangerous to those who live near warming sites.
When underlying permafrost begins to warm, it thaws and can no longer support the soil above it. Depending how much permafrost sits beneath a region, the ground can become highly unstable.
“Say you take a pork chop out of the freezer—it won’t melt away. It will shift from a frozen state to a thawed state,” said Sarah Godsey, a professor at Idaho State University who has studied permafrost melt in Alaska. “But if that pork chop was 50 percent ice, you’d have a different story. Ice content is really important.”
Thermokarst has been observed previously in the Qinhai-Tiber Plateau. A study published in the journal Scientific Reports noted in May that desertification in the region was contributing to permafrost thaw.
However, it’s unclear whether thawing permafrost is to blame for this particular earth flow, or whether unusually warm weather thawed a top layer of temporarily frozen soil. Scientists say that it’s impossible to decisively determine what caused the landslide from the video alone.
Without obvious chunks of frozen material visible in the video, it’s unclear whether permafrost in the area has thawed, according to McKinnon.
In response to the video, McKinnon and a colleague from Tibet worked to find satellite images that would provide a better before-and-after look at the region, but geopolitical tensions made the task difficult. A village name used by local Tibetans, for example, may not be reflected in Chinese satellite images.
Godsey agreed that without studying the soil composition in the area, stating for certain that the earthflow was caused by thawing permafrost was difficult to say. She noted differences in a video she published in 2010 that shows thawing permafrost in Alaska.
Where Is Permafrost Thawing?
While we don’t know for sure that the earthflow in Tibet was caused by thawing ground ice, it’s a problem happening around the world that promises to have big impacts. (Read about how thawing permafrost is exposing Alaska's ancient artifacts.)
In an email with National Geographic, University of Sussex geography professor Thomas Opel noted that he saw a slide similar to the one in Tibet in the Siberian Arctic.
“In many regions, the depths of the seasonal thawing have increased due to climate warming,” he says.
As greenhouse gases increase global temperatures, he says, warming permafrost can in turn release a slew of carbon and further raise temperatures.
McKinnon observed that the video shows landslide scars on hills in the surrounding regions, meaning this likely isn’t the first time the ground has shifted beneath the surface in this region. However, more research is needed to pinpoint where those landslides came from.
As with most landslides, she observed, it usually begins slowly and becomes evident all at once.