Health/Sci-TechLifestyleVOLUME 19 ISSUE # 17

Mystery of enormous Saharan ‘star dune’ finally solved

A towering, star-shaped dune in the Sahara desert formed in less than a thousand years, new research finds.

The study, published in the journal Scientific Reports, is one of relatively few to look at these so-called star dunes, which are the tallest dunes on Earth. Named for their multiple-armed shapes, star dunes form in places where the winds change direction throughout the year, according to the National Park Service.

Although star dunes are found all over the world, there is only one confirmed star dune in the rock record, from about 250 million years ago in Scotland, Charles Bristow, a professor emeritus of sedimentology at University College London, told Live Science. That may be because researchers don’t know what to look for to identify an ancient star dune, he said.

These dunes are difficult to study because they’re usually in remote locations, and slogging up a few hundred feet of shifting sand is not easy. The dune is in Morocco in a dune field called Erg Chebbi. Luckily for the researchers, the area has become a popular tourist stop, so there are good roads and hotels around the edges of the dune field.

The dune itself is about 330 feet (100 meters) tall. It’s known as Lala Lallia by locals. To collect data on the dune, Bristow, study co-author Geoff Duller of Aberystwyth University and research students used ground-penetrating radar, which can detect small differences in sand grain sizes and water content beneath the dune’s surface. This technique allowed the researchers to build a picture of the dune’s interior layers.

They also dug trenches to take samples of long-buried sands. The quartz in the sand accrues radiation from natural sources within the Earth while buried. By shining a laser on the quartz, researchers can measure this radiation and determine when the sand last saw the surface. This look inside the dune revealed a surprisingly short history. “The thing that stood out most was how young it is,” Bristow said. “We expected that a sand dune that is 100 meters high was going to be quite old … thousands of years, maybe tens of thousands of years. And it turned out that this dune was 900 years old.”