In the Sahara Desert, rare sand dunes are emerging from three ancient black mesas, located near Guérou in southern Mauritania. This noteworthy geological formation was captured in a photograph taken by an astronaut aboard the International Space Station on May 3, 2023.
The Black Mesas of Mauritania
The three mesas, resembling flat-topped hills, are situated approximately 8 miles (13 kilometers) northwest of the town of Guérou, which has a population of about 22,000. These sandstone formations rise between 1,000 and 1,300 feet (300 and 400 meters) above the desert floor. The largest mesa spans around 6 miles (9.5 kilometers) at its widest point. A fourth mesa lies just north but is not visible in the photograph.
Rock Varnish and Formation
The striking dark color of the mesas comes from a natural process known as rock varnish. This clay-based coating contains manganese and iron oxides, developing over thousands of years on exposed rock surfaces. Microorganisms may have played a role in stabilizing this coating, which consists of multiple thin laminations.
Sand Dune Dynamics
Notably, the area west of the mesas features a barren rocky plain with an absence of sand dunes. In contrast, the eastern side showcases several sand dunes that appear to flow away from the black mesas. The two predominant types of dunes observed include:
- Climbing dunes: These are ridge-like formations accumulating along the eastern walls of the mesas.
- Barchan dunes: More commonly seen, these create a ripple effect stretching across the mesa’s tail.
Both types of dunes exhibit a reddish-yellow hue. The formation of sand dunes on the eastern side is due to prevailing winds that carry sand toward the mesas, while wind scour prevents accumulation to the west.
Historical Context
These mesas were likely part of a larger rock formation during the Paleozoic era, which spanned from approximately 541 million to 251.9 million years ago. Erosion over millennia has fragmented this geological marvel. Similar formations, such as the Richat Structure—also known as the “Eye of the Sahara”—are located further north in Mauritania.
Global Context of Mesas
While mesas can be found globally, their concentration in the Sahara is notable. They also exist in parts of the United States, specifically in states like Colorado, New Mexico, Utah, and Arizona. Additionally, mesas can be observed on Mars, shaped by extensive wind erosion over billions of years.
For more captivating images and insights from space, visit El-Balad. This exploration highlights the stunning natural phenomena found in our ever-evolving world.
