A Lake Materializes in the Sahara Desert, Offering a Glimpse Into Africa’s Past

Behold Sebkha el Melah, an ephemeral lake in Algeria, seen from space.

The lake formed after a cyclone walloped parts of northern Africa in September, causing huge amounts of rain in the Sahara Desert. And now, it’s helping researchers study what the Sahara may have looked like thousands of years ago—perhaps not a jungle, but a much wetter environment than it is today. Deserts generally get less than four inches of rain per year, according to the National Science Foundation, indicating how important an ephemeral lake can be for life in the world’s largest non-polar desert.

You can see the region of Algeria as it appeared in August and September 2024 below. There is one obvious dark-green difference. The rain came in earlier September and soaked parts of Morocco, Algeria, Tunisia, and Libya.

The images were taken by the Operational Land Imager-2 (OLI-2) aboard NASA’s Landsat 9. As of last week, the lake was about 33% full and covered an area of 74 square miles (191 square kilometers) to a depth of about 7.2 feet (2.2 meters), according to Moshe Armon, a researcher at the Hebrew University of Jerusalem, who reviewed satellite images of the lake.

Between 11,000 to 5,000 years ago, a wobble in Earth’s orbit turned the Sahara into a lusher environment than it is today. It was the African Humid Period, during which ancient humans painted animals and hunting scenes in caves and on rocks across now-dried-up swaths of countries including Egypt, Chad, and Sudan. Lake levels across northern Africa were much higher than they are today, and the region much much verdant. But some geologists argue that climate conditions during that period could not have generated enough rain to fill the number of lakes researchers estimate existed in what is now the Sahara.

“We’re proposing a third option: that extreme rain events, like the one in September in the northwestern Sahara, might have been more frequent in the past,” Armon said in the Earth Observatory release. “Given how long it takes lakes to dry up, these events could have been common enough to keep lakes partially filled over long periods—even years or decades—without frequent rainfall.”

Sebkha el Melah could stay filled for years. When the salty lakebed filled in 2008, the water didn’t completely evaporate until 2012, according to a NASA Earth Observatory release. “If we don’t get any more rain events,” Armon said, the lake “would take about a year to evaporate completely.”

The summer tends to be a wetter time of year for the Sahara. Of 38,000 recorded heavy precipitation events in the the desert, about 30% occurred during the summer, according to an earlier Earth Observatory release.

Eyes from the sky increasingly help scientists monitor Earth’s water. In 2022, NASA and France’s CNES launched the Surface Water and Ocean Topography (SWOT) mission, a three-year venture that collects data on water volume and movement from orbit. Other spacecraft, like NASA’s Deep Space Climate Observatory (DSCOVR), keep track of atmospheric climate events.

Whether the lake stays filled for months or years, it serves as a reminder of how dramatically landscapes—and our understanding of them—can shift with the planet’s changing climate.