If you didn’t know better, you might think the above is an image of water rippling over a colorful lake bottom, or an abstract painting of sorts. The reality is that this is an image of the Earth – specifically a sun-drenched area of the Sahara Desert – as captured by NASA’s Landsat 7 satellite, which probably passed over the region a little before 10AM local time, according to our sources at NASA. The image shows ‘ribbons’ of sand and patterns of stripes from linear dunes in the uninhabited Erg Chech region of southwestern Algeria.
In the case of this satellite image, light from the shallow-angled rays of the setting sun, gives us this incredible view of a remote place with an incredible and otherworldly color scheme.
The Erg Chech dunes are parallel, straight ridges of sand that can run for as long as 99 miles, and their exact cause and origin is still under question. According to io9, one theory puts helical roll vortices as the cause of their formation. Formulated in 1969 by Stephen Hanna, this phenomenon involves prevailing spiraling twists of wind that deposit sand where they intersect and create the dunes at the boundaries of the wind spirals.
“The dunes are aligned in the direction of the prevailing wind and are spaced 1.2 miles apart,” Hanna noted in his research for the Air Resources Atmospheric Turbulence and Diffusion Laboratory of the National Oceanic and Atmospheric Administration (NOAA).
“Observations in the atmosphere and in the laboratory indicate that dominant forms of motion in the boundary layer of the atmosphere are counter-rotating helical roll vortices aligned along the wind,” Hanna continues. “The necessary conditions for the formation of these roll vortices are fulfilled over large deserts and their spacings agree with the observed spacings of the dunes.”
Another theory posits that two near-parallel prevailing wind directions in a specific location could result in this kind of dune formation. In this case, the winds come together at the correct angle to create a “dead zone of deposition,” which results in the formation of the dune.
Whatever the theory, the results are incredible and another example of the Earth’s incredible artistry.