Scientists Unravel the Mysteries of Earth’s Towering Star Dunes—Massive, Moving Mountains of Sand

From the ground, star dunes look like towering, pyramid-shaped mounds of sand. But when viewed from above, their namesake shape becomes more obvious: Tendrils of sand radiate out from a central peak, giving the dunes a resemblance to starfish.

On Earth, star dunes have been identified in the deserts of China, Namibia, Algeria, Saudi Arabia and the United States. They’ve also been spotted on Mars, as well as on Saturn’s largest moon, Titan. The structures can stand up to 1,000 feet tall, making them some of the tallest dunes on Earth, reports Reuters’ Will Dunham.

Scientists have long been intrigued by these large, unusually shaped formations, but they haven’t been able to answer even some of the most basic questions about them. Now, in a new paper published Monday in the journal Scientific Reports, researchers begin to unravel some of the mysteries surrounding star dunes, painting a clearer picture of their dynamics.

“It’s only because of new technology that we can now start to uncover their secrets,” says study co-author Geoff Duller, a geographer and Earth scientist at Aberystwyth University in Wales, in a statement.

For the study, Duller and his colleagues focused their attention on a star dune in eastern Morocco named Lala Lallia, which means “highest sacred point” in the local Berber language. The dune is located in the Erg Chebbi region of the Sahara Desert, not far from the town of Merzouga near the border with Algeria. 

As its name suggests, Lala Lallia is massive, standing roughly 330 feet taller than the surrounding dunes and measuring 2,300 feet wide. Scientists estimate the structure is made up of about 5.5 million metric tons of sand. Such dunes are “extraordinary and awe-inspiring,” says study co-author Charles Bristow to Reuters. “From the ground they can be intimidating.”

To learn more about Lala Lallia, scientists walked over the dune and stopped every 1.6 feet to use ground-penetrating radar. The radar produced high-resolution images of the sediment layers that make up the dune.

They also collected samples of sand from different depths, which they took back to their lab to analyze with a technique called luminescence dating. This method helped them determine when the sand was blown onto the dune and sketch out a timeline of its creation.

“We’re not looking at when the sand was formed—that’s millions of years ago—but when it was deposited,” Duller tells the Guardian’s Steven Morris. “The grains of quartz have a property like a mini rechargeable battery. It can store energy that it gets from naturally occurring radioactivity. When we bring it back to the laboratory, we can get it to release that energy. It comes out in the form of light. We can measure that and the brightness tells us the last time the sand grain saw daylight.”

Based on their measurements, scientists think the base of Lala Lallia is 13,000 years old. It grew for roughly 4,000 years, then stopped growing for approximately 8,000 years. Around 1,000 years ago, it started growing rapidly again and began to take on its distinctive star shape.

“I found their results very interesting, because like most people, I had not suspected that star dunes could accumulate so quickly,” Andrew Goudie, a geographer at the University of Oxford in England who was not involved with the study, tells CNN’s Mindy Weisberger.

The star shape formed because the wind around the dune is blowing in opposite directions—some from the southwest and some from the northeast. These opposing forces are what have created the arms of the star.

In addition, wind also comes from the east, pushing the entire dune slowly to the west at a rate of about 1.6 feet per year. That discovery could have practical implications for development projects near star dunes, researchers say.

“That’s important when you’re thinking about building roads, pipelines or any sort of infrastructure,” Duller tells the Guardian. “These things actually do move.”

The findings also shed light on a long-standing geological mystery. Star dunes are relatively common today, making up roughly 10 percent of all dunes on Earth, per Reuters. But only one ancient star dune has ever been discovered. Located in Scotland, it’s roughly 250 million years old and made up of preserved layers of sandstone. Why aren’t there more?

Now, the researchers believe that ancient star dunes may be hiding in plain sight. Star dunes are so large that scientists may have mistaken parts of them for other types of dunes—they might just need to zoom out a bit to see the full, star-shaped picture.

“When you look at each piece individually of a star dune in the geological record, it’s going to look like something else,” Duller tells CNN. “But when you get all of these pieces together—and you can see these large troughs of cross-bedded sands in the middle, you can see these arms stretching out in each direction—that’s when you can confidently say it’s a star dune.”

Sarah Kuta | READ MORE

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.