Three shadowy plateaus rising from the endless sands of Mauritania have captivated scientists once again. A recent observation by NASA’s Earth Observatory revealed how these “black mesas”, relics of the Paleozoic Era, are still shaping the desert today—forming dunes that stretch for miles and even carving out wind-swept voids visible from orbit.
A Snapshot From Space
When an astronaut aboard the International Space Station captured a high-resolution image of southern Mauritania in May 2023, what appeared was more than just a desert landscape. Three nearly identical, dark-topped hills—known as mesas—stood side by side, framed by long tails of rippling sand. To the east, delicate dunes shimmered in hues of red and gold; to the west, the sands vanished completely. According to NASA’s Earth Observatory, this stark contrast is not random but the product of ancient geology interacting with modern atmospheric forces.
Credit: NASA’s Earth Observatory
These mesas, each flat-topped and nearly circular, are coated in a thin layer of rock varnish, a naturally occurring glaze formed by clay, manganese, and iron oxides over thousands of years. This varnish, fixed in part by microorganisms, gives the mesas their striking black hue—making them appear like shadows cast upon the Sahara’s pale floor. The varnish has survived millions of years of erosion, standing as testimony to the planet’s enduring geological memory.
The Desert’s Dual Personality
What makes the scene so extraordinary is the juxtaposition of two opposing worlds: dunes on one side and bare rock on the other. The Earth Observatory reports that strong, persistent winds blow from the east, carrying sand grains that gather along the mesas’ slopes, creating “climbing dunes” that appear to scale the rocky walls. These massive ridges feed into sweeping arcs of barchan dunes—crescent-shaped sand waves that stream out like tails behind the mesas.
To the west, however, there is silence. Here, high-velocity air currents whip through narrow gaps between the mesas, creating wind scour, a phenomenon that sweeps sand away instead of depositing it. The result is a “dune-free zone,” a barren corridor in a sea of dust. This delicate balance of airflow, topography, and mineral surface explains why sand behaves so differently on either side—a small but fascinating meteorological puzzle visible from hundreds of miles above Earth.
Echoes From the Paleozoic
Geologists believe that during the Paleozoic Era—between 541 and 252 million years ago—all three mesas were once part of a single, vast rock formation. Over millions of years, relentless cycles of erosion by water and wind fractured the structure into the isolated towers we see today. These remnants are akin to the Richat Structure, also known as the “Eye of the Sahara,” located roughly 460 kilometers north of Guérou, Mauritania.
The mesas are part of a broader family of formations found across the planet, from the deserts of the American Southwest to the Martian surface, where similar erosional features testify to ancient climatic activity. The image captured by astronauts thus bridges Earth and Mars—two worlds sculpted by the same relentless natural forces.
