A research team has uncovered how deep lakes once filled remote craters high in the Tibesti Mountains, offering new insight into climate patterns in one of the driest regions on Earth. The scientists revealed that crater lakes in the Sahara mountains, now long vanished, were sustained by unexpected rainfall patterns more than 7,000 years ago.
The study, published in Nature Communications, was led by researchers from Freie Universität Berlin and the Max Planck Institute for Meteorology. It confirms that these lakes began forming over 9,500 years ago and remained for more than 5,000 years — a rare hydrological phenomenon in a region now known as part of the vast Sahara Desert.
The findings highlight a sharp contrast between the present-day arid conditions and the lush, lake-filled landscapes that existed during the North African Humid Period. These shifts were particularly evident in the Tibesti region, located in modern-day northern Chad, which rises dramatically above the surrounding plains.
Historical expeditions and field research
Historical interest in the area dates back to 1869, when German explorer Gustav Nachtigal first documented a deep volcanic crater at an elevation of about 2,500 meters (8,202 feet). Known locally as Doon Orei and in French as Trou au Natron, this crater was one of several that held freshwater lakes thousands of years ago.
More recently, geologist Stefan Kröpelin from the University of Cologne led field expeditions to Trou au Natron and the nearby Era Kohor crater, located within the Emi Koussi caldera, which reaches an elevation of 3,500 meters (11,483 feet).
The team collected sediment cores from the ancient lake beds and transported them to Germany for detailed analysis, despite the region’s harsh climate and logistical challenges.
At the Laboratory for Physical Geography at Freie Universität Berlin, geochemists examined the sediment layers to reconstruct the history of the lakes.
Philipp Hoelzmann, a geographer and one of the lead authors, explained that studying these well-preserved samples allowed the team to track how and when the lakes formed and disappeared.
Advanced climate modeling provides new insights
The researchers extended their analysis by using high-resolution paleoclimate models at the Max Planck Institute for Meteorology. These simulations, based on data from around 7,000 years ago, had a fine spatial scale of roughly five kilometers (3.1 miles).
Martin Claussen, head of the climate modeling group, explained that this was the first time scientists were able to accurately simulate the steep terrain and rainfall behavior in the Tibesti region.
Their results showed that rainfall in the Sahara mountains was at least ten times greater in the Tibesti than in the surrounding lowlands. Contrary to earlier theories, the moisture originated not from the south via the West African monsoon but from the northeast.
Winds from the Mediterranean transported moist air toward the highlands, where the mountain slopes forced the air upward, causing heavy precipitation that fed the crater lakes.
Shifting theories on the Sahara’s climate history
The team also utilized remote sensing and terrain analysis to map the region’s hydrology. A numerical water balance model supported their findings, showing that these high-altitude lakes were sustained by consistent rainfall over the centuries.
Researchers emphasized that these results demonstrate the importance of high-resolution climate modeling in reconstructing regional environmental changes.
They say the same methods could prove crucial for understanding how landscapes like the Sahara may respond to current and future climate shifts.
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