Mysterious rings in the Sahara Desert have a fiery origin

Today’s Image of the Day from NASA Earth Observatory highlights a solitary mountain lifting out of the Sahara.

In this extremely dry part of the desert, a set of dark massifs cuts across the wide expanse of light-colored sand.

The difference in color and texture is so sharp that these outcrops seem almost like stranded islands.

Isolated outcrops with their own history

One of the most eye-catching formations is Jabal Arkanū in southeastern Libya, a circular mountain ringed by patterns that stand out sharply from the desert floor. 

The rings look unusual at first glance, and people have wondered about them for years.

These shapes appear in a part of northeastern Africa where the landscape barely changes from season to season due to the lack of rain. Yet the geology here tells a story of forces that once moved deep below the surface. 

The mountain sits close to other isolated outcrops, each shaped by its own history and chemistry.

It’s an area that feels tucked away from the rest of the world, but it has drawn steady curiosity from researchers working to piece together the region’s past.

The story behind the Sahara rings

Early work on similar circular structures nearby suggested they came from meteorite impacts. That idea caught on for a while, mainly because the Sahara is full of craters from ancient collisions and the shapes seemed to fit. 

Later field studies challenged that interpretation, pointing instead to rock textures and patterns that only form through processes inside Earth. Over time, the evidence pulled researchers toward a different explanation.

Studies found that the rings at Arkanū formed as magma pushed upward and intruded into the surrounding layers. 

These intrusions happened more than once, building up several overlapping rings with centers that line up toward the southwest. 

The complex includes basalt and granite, which cooled and hardened long before the sand we see today covered the plains.

North of the rings, a hat-shaped structure made of sandstone, limestone, and quartz caps the edge of the massif.

Viewing the mountain from space

This latest photograph, taken by an astronaut aboard the International Space Station on September 13, 2025, shows the massif with long shadows stretching across the desert. 

The ridges rise to nearly 4,600 feet above sea level, standing around 2,600 feet above the sandy flats around them. From orbit, the contrast between stone and sand jumps out clearly.

Broad fans of boulders, gravel, and sand spill outward from the base of the mountain. These outwash fans spread until they reach a chain of long, straight dunes that run parallel to the prevailing winds. 

Two wadis cut through the massif as well, but they rarely carry water because the regional climate is so dry.

A landscape with rare rainfall

Rain is hard to come by in this part of Libya. Data from the Tropical Rainfall Measuring Mission, run by NASA and JAXA, revealed that southeastern Libya and neighboring parts of Egypt and Sudan receive only about 0.04 to 0.2 inches of rain each year. 

Slightly higher totals, around 0.2 to 0.4 inches, fall near Jabal Arkanū and nearby mountains.

This small bump hints at a subtle orographic effect, where moist air rises along the slopes and releases tiny amounts of rain.

It’s not enough rainfall to support much vegetation, but it explains why the nearby massifs get a touch more moisture than the open desert.

Why these formations matter

Remote features like Arkanū help scientists understand how magma once moved beneath the Sahara and how old crustal blocks fit together. 

These mountains offer rare windows into deeper layers that are usually hidden underground. Their isolation helps preserve rock faces that would be eroded or altered in wetter environments.

They also stand as natural records of changes in climate. Even a wadi that stays dry most years can hold clues in its sediments about periods when rain briefly returned. 

Knowing how rainfall patterns shifted over time can help researchers piece together the broader climate history of northern Africa.

Forces beneath the surface

Jabal Arkanū may look lonely out there, but it shares the region with other massifs. Jabal Al Anaynat is about 12 miles to the southeast, and the Arkenu structures lie roughly 56 miles to the west.

Each has its own ring patterns, slopes, and stone layers. Together, they show how varied the geology of the Sahara can be, even in places that seem empty from afar.

What we see in today’s photograph is the end result of pressures that once reshaped rock far below the surface. 

Image Credit: NASA Earth Observatory

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–