On December 29, 2024, an astronaut aboard the International Space Station captured a striking photograph that could change the way we think about the Sahara Desert. High above the vast sands of northern Chad, the image reveals a surprising sight atop the Emi Koussi volcano, the highest peak in the Sahara.
At first glance, the patch of white at the summit appears to be snow, an unusual occurrence in one of Earth’s driest regions. But upon closer inspection, the true nature of the patch is revealed — it is a salt-covered lake bed, a remnant of the Sahara’s wetter past.
A Volcanic Giant in the Heart of the Sahara
Emi Koussi is no ordinary mountain. Standing at 3,415 meters (11,204 feet), it is not only the tallest volcano in the Sahara but also a central feature of the region’s geological history. The volcano’s massive cone spans 70 kilometers in diameter, making it an imposing landmark in the otherwise flat desert landscape.
The image captured from space focuses on the summit of this colossal structure, which sits at the rim of an elliptical caldera. The white patch is located at the caldera’s lowest point, approximately 745 meters below the peak, providing a striking contrast to the surrounding rocky slopes.
While snow in the Sahara is rare, this particular patch is not an anomaly of weather but a geological one. The salt covering the lake bed is a clue to the region’s ancient climate. According to the NASA Earth Observatory, the small lake that once filled this caldera has long since dried up, leaving behind the salt deposits visible today.
The salt bed’s whiteness serves as a reminder of a time when the Sahara was much wetter, with occasional lakes and rivers that sustained life in a far more hospitable environment than the one we see today.
Evidence of Ancient Water Systems
Beyond the salt lake, the photograph also reveals several erosion channels running down the flanks of Emi Koussi. These channels, thin and winding, offer further evidence of water’s presence in the Sahara’s distant past. Despite the region’s current aridity, geologists believe that these channels were carved over thousands of years by water runoff.
The relatively low rainfall in the region today suggests that the channels were formed during a wetter period, when water intermittently flowed through the area. These marks left by ancient water systems challenge the common perception of the Sahara as a static desert, offering a glimpse into a dynamic past.
The presence of these features paints a picture of a region once shaped by both volcanic activity and the slow erosion caused by occasional water flows. As the photograph shows, the canyons between Emi Koussi and nearby Tarso Ahon, another large volcanic mountain, were formed by the runoff of water from both volcanoes. These deep canyons, which cut through the desert landscape, serve as a testament to the power of water in shaping the region’s topography.
A Shift in Understanding the Sahara
The photograph taken from the ISS does more than document a volcanic feature of the Sahara. It challenges the conventional image of the desert as a barren expanse of sand dunes. Instead, it reveals a complex landscape shaped by volcanic forces and the occasional presence of water.
While the Sahara is known for its extreme dryness today, it holds clues to a past that was far wetter and more dynamic. This discovery is not just a geological observation but also an invitation to reconsider the history of one of Earth’s most iconic deserts.
