Rings of Rock in the Sahara
In northeastern Africa, in the driest part of the Sahara, dark rocky outcrops rise above the pale desert sands. Several of these formations, including Jabal Arakanū, display striking ring structures.
Jabal Arkanū (also spelled Arkenu) is in southeastern Libya, near the border with Egypt. Several other massifs are grouped nearby, including Jabal Al Awaynat (or Uweinat), located approximately 20 kilometers (12 miles) to the southeast. About 90 kilometers to the west are the Arkenu structures of the same name. These circular features were once thought to have formed by meteorite impacts, but later field work suggested they resulted from terrestrial geological processes.
Arkanū’s ring-shaped structures also have an earthly origin. They are thought to have formed when magma rose toward the surface and penetrated the surrounding rock. Repeated intrusion events have produced a series of overlapping rings, the centers of which are roughly aligned to the southwest. The resulting ring complex, composed of igneous basalt and granite, is bordered to the north by a hat-shaped formation composed of layers of sandstone, limestone and quartz.
This photograph, taken by an astronaut aboard the International Space Station on September 13, 2025, shows the massif casting long shadows on the desert. The ridges rise almost 1,400 meters above sea level, or about 800 meters above the surrounding sandy plains. Note several fans of rock, gravel, and sand extending from the base of the mountain toward the adjacent longitudinal dunes.
Two wadis, or generally dry river beds, meander through the structure. However, water is scarce in this part of the Sahara. Previous research using data from NASA and JAXA’s now-completed Tropical Rainfall Measuring Mission (TRMM) has indicated that southeastern Libya, as well as adjacent areas of Egypt and northern Sudan, receive only about 1 to 5 millimeters of rain per year. Slightly higher accumulations, around 5 to 10 millimeters per year, occur near Jabal Arkanū and neighboring ranges, suggesting a modest orographic effect of the mountains.
Astronaut photograph ISS073-E-698446 was acquired on September 13, 2025 with a Nikon Z9 digital camera using a focal length of 800 millimeters. It is provided by the ISS Crew Earth Observation Facility and Johnson Space Center’s Earth Science and Remote Sensing Unit. The image was taken by an Expedition 73 crew member. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station program supports the laboratory as part of the ISS National Laboratory to help astronauts take photos of Earth that will be of the greatest value to scientists and the public, and to make these images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed on the NASA/JSC Gateway to Earth Astronaut Photography. Story by Kathryn Hansen.
- Afkareen, MM, and others. (2022) Linear mapping of Jabal Arkenu in southern Libya. The scientific journal of the University of Benghazi35(1).
- Alghariani, M. (2020) Applications of remote sensing for the exploration of mineral deposits and gold in Jabal Arkenu. Fourth International Conference on Geospatial Technologies Libya GeoTec4 in Tripoli – Libya.
- Cigolini, C., and others. (2012) Endogenous and impact-free origin of the circular structures of Arkenu (al-Kufrah basin – SE Libya). Meteoritics and planetary sciences47(11), 1772-1788.
- Kelley, OA (2014) Where precipitation is lowest in the Sahara Desert, TRMM radar reveals a different precipitation pattern each season. Climate Journal27(18), 6919-6939.
- NASA Earth Observatory (January 23, 2024) Water under the sand. Accessed October 30, 2025.
- NASA Earth Observatory (March 9, 2013) Jebel Uweinat. Accessed October 30, 2025.
- NASA Earth Observatory (November 10, 2008) Arkenu Craters, Libya. Accessed October 30, 2025.
