This satellite image shows the stark contrast between the “star dune” field in Algeria and the rocky terrain found mostly in Libya. (Image credit: NASA/EarthKAM) SUMMARY
Where is it? Grand Erg Oriental, Sahara [30.13306820, 9.306920931]
What's in the photo? A stark contrast: a field of “star dunes” meets rocky hills.
Which satellite took this photo? The EarthKAM camera on board the International Space Station.
When was this done? October 31, 2017.
This stunning satellite image demonstrates the striking difference between the giant field of sand “stars” and the barren, rocky Sahara Desert. The contrasting biomes also intersect at the border between the two African countries.
The sea of orange sand seen in this image is part of the Grand Erg Oriental, a giant dune field, or erg, that covers about 55,000 square miles (140,000 square kilometers) in the northern Sahara.
This part of the erg boasts hundreds of distinctive “star dunes,” which consist of at least three ridges extending from a central peak, giving them the appearance of a star from above. Star dunes can reach heights of over 90 meters and form only in areas with constant wind shifts, which, according to the National Park Service, contributes to the formation of their varied slopes.
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The dunes are capped by a windswept, rocky landscape that, according to NASA's Earth Observatory, is one of the “driest parts of the Sahara Desert” and is virtually devoid of vegetation. This landscape is covered in overlapping geological formations, giving it an otherworldly appearance.
One of the most striking features is a large white spot in the heart of the rocky terrain, representing the remains of an ancient lake. You can also see a series of parallel grooves in the rock (in the upper half of the rocky terrain), carved by centuries of winds blowing in the same direction long before the multifaceted dunes were formed.
Experts believe that much of the sand in the satellite image is likely of rocky origin from the surrounding rocky terrain.
All the dunes in the image are in Algeria, while most of the rocky terrain is in Libya. The invisible border between the two countries runs almost down the center of the image. However, in one spot, just to the left of the Libyan city of Ghadames (visible as a dark spot at the top of the image), the border between the countries almost exactly coincides with the line where the sand and rock meet.
Although these contrasting ecosystems seem to have nothing in common, they are linked far more closely than one might imagine. Geologists believe that much of the erg's sand was deposited by ancient rainwater, which carried loose sediments from the rocky terrain and deposited them into natural depressions, or basins, in the landscape.
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According to the Earth Observatory, this process likely took hundreds of thousands, if not millions, of years, and if you look closely, you can see that some of the sand from the erg has flowed back into ancient “meandering streams” that helped deposit the sand within the erg.
The erg is also partially formed over an ancient riverbed. When rainfall is infrequent on the erg's sands, the moisture drains into underground aquifers, which can support patches of vegetation on the surface. Without this, this valuable moisture would quickly evaporate back into the atmosphere.
TOPICS Earth from Space
Harry Baker, Social Link Navigation, Senior Staff Writer
Harry is a senior writer for Live Science based in the UK. Before becoming a journalist, he studied marine biology at the University of Exeter. He covers a wide range of topics, including space exploration, planetary science, space weather, climate change, animal behavior, and paleontology. His recent work on solar maximum won the 2024 Aerospace Media Awards in the Best Space Story category and was shortlisted for the 2023 NCTJ Awards for Excellence in the Breaking News category. He also writes Live Science's weekly series, “Earth from Space.”
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