Videos from Mongolia provide humanity with its first ever view of the Earth’s crust moving.
On 17 July 2018, a Facebook user shared two dramatic videos of geological phenomena in a now-viral Facebook post accompanied by a not-at-all accurate description:
This post’s description of the videos was perplexing for several reasons. First, these videos did not capture events that occurred recently, did not document the same event, and did not offer visual recordings of “the moving of earth crust.”
The first video was of a landslide that took place in the southern Italian town of Maierato in February 2010. NASA’s Earth Observatory provides an explanation for the event (and some impressive before and after satellite imagery of it), linking this landslide and several related ones to heavy rainfall in the region:
Gravity constantly tugs downward on a slope, but only when gravity’s force exceeds the strength of the rocks, soils, and sediments composing the slope does land begin to slide down hill. Landslides often occur in conjunction with other events, and rainfall in the Maierato region likely initiated this slide.
The lower video was from Inner Mongolia (which is not the country of Mongolia but rather a semi-autonomous region of China) and captured a landslide occurring there on 10 September 2017. Wang Dejun, director of the Institute of Geological and Natural Disaster Prevention of the Gansu Academy of Sciences, told China’s Science and Technology Daily that (roughly translated):
This is an intermediate state between the debris flow and the landslide. It is a very normal natural phenomenon. After the frozen saturated soil layer and the weathered layer are thawed, this [phenomenon] occurs along the slope due to gravity, slowly flowing or creeping.
Areas with melting permafrost, such as the high-altitude region of Inner Mongolia where this debris flow occurred, experience this kind of phenomenon frequently, making it highly unlikely this was the “first time mankind has seen this happen,” as Science and Technology Daily observed:
The unique geographical environment of the Qinghai-Tibet Plateau provides an excellent environment for the formation of frozen mudflows. For thousands of years, [such flows have been] like sunrise and sunset.
When the soil layer is frozen in winter, the soil particles bulge along the slope. When the later melts in the summer, it will fall back in the vertical direction, so that the soil particles will be displaced downwards in the direction of the slope, and will be converted into muddy flow in the case of super-saturated water.
The Italian landslide, though massive in scale, was similarly not a rare or unique kind of event unwitnessed by humanity until now. As described by NASA, the video captured was “one of perhaps 100 landslides in the southern Italian region of Calabria” attributed to a single rain event.
Finally, what is being displayed in both videos is not “moving crust” but merely surface debris unable to fight Earth’s gravity. “Crust,” geologically speaking, refers to the layer of rock that surrounds our planet and rests on the more ductile mantle below. Discussion of the movement of crust generally occurs on either extremely long timescales or involves extremely short distances and is usually discussed in terms of interactions of the various tectonic plates that comprise Earth’s crust. Therefore, “moving crust” is an incorrect description of what is depicted in these videos.