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.