Watch the salt lake, a rapidly disappearing lake in Algeria, as seen from space.
The lake was formed after a hurricane hit parts of North Africa in September, causing massive rainfall in the Sahara Desert. It is now helping researchers study the appearance of the Sahara Desert thousands of years ago, which may not have been a forest, but was a more humid environment than it is today. Rainfall in deserts generally is less than four inches annually, according to the National Science Foundation, highlighting the importance of the rapidly disappearing lake 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 clear difference in the dark green color. Rain fell in early September and flooded parts of Morocco, Algeria, Tunisia, and Libya.
The images were captured by the Operational Land Imager-2 (OLI-2) on board NASA’s Landsat 9. As of last week, the lake was filled to about 33% and covered an area of 74 square miles (191 square kilometers) at a depth of about 7.2 feet (2.2 meters), according to Moshe Armon, a researcher at the Hebrew University in Jerusalem, who reviewed satellite images of the lake.
Between 11,000 and 5,000 years ago, Earth’s orbit oscillation transformed the Sahara Desert into a more fertile environment than it is today. It was the African humid period, where ancient humans depicted animals and hunting scenes in caves and on rocks across dry expanses of countries including Egypt, Chad, and Sudan. Lakes levels throughout North Africa were much higher than they are today, and the area was much greener. However, some geologists say that the climatic conditions during that period could not generate enough rainfall to fill the number of lakes estimated by researchers to have existed in what is now the desert.
Armon said in a statement from the Earth Observatory: “We suggest a third option: that heavy rainfall events, like those that occurred in September in northwest Sahara, may have been more frequent in the past.” “Considering the time it takes for lakes to dry up, these events could have been common enough to keep the lakes partially filled for long periods – even years or decades – without repeated rainfall.”
The salt lake can remain filled for years. When the bottom of the salt lake was filled in 2008, the water did not completely evaporate until 2012, according to a release from NASA’s Earth Observatory. Armon said, “If we do not see more rainfall, the lake will take about a year to completely evaporate.”
Summer tends to be a more humid time of year for the desert. Among 38,000 cases of heavy rainfall recorded in the desert, about 30% of them occurred during the summer season, according to a previous release from the Earth Observatory.
Eyes from the sky are increasingly helping scientists monitor Earth’s water. In 2022, NASA and the French National Center for Space Studies (CNES) launched the Surface Water and Ocean Topography (SWOT) mission, a three-year project that collects data on water volume and movement from orbit. Other spacecraft, like NASA’s Deep Space Climate Observatory (DSCOVR), track weather events.
Whether the lake remains filled for months or years, it serves as a reminder of how drastically landscapes have changed – and our understanding of them – with the planet’s changing climate.
