Stellar Dunes: Scientists solve the mystery behind the largest desert sand on Earth

The age of one of the largest and most complex types of sand dunes on Earth has been calculated for the first time.

Star dunes – or pyramid dunes – are named for their distinctive shapes, and they reach hundreds of meters in height.

It is found in Africa, Asia, North America, as well as on Mars, but experts have not previously been able to determine a date for its formation.

Scientists have now discovered that the sand dunes called Lala Lalia in Morocco were formed 13,000 years ago.

Stellar dunes are created by headwinds that change direction. Understanding their age helps scientists understand those winds and the climate of that era, says Professor Geoff Dowler from Aberystwyth University, who published the research with Professor Charles Bristow at Birkbeck University.

Lala Lalia (an original Berber name meaning the highest sacred point) is located in the sandy Erg Chebbi Sea in southeastern Morocco. It is 100 meters high and 700 meters wide and has radiating arms.

After its initial formation, it stopped growing for about 8,000 years and then expanded rapidly in the past several thousand years.

Deserts can usually be identified in Earth's geological history, but stellar dunes have been absent until now.

Professor Dowler says this may be because the dunes are so large that experts did not realize they were looking at a distinctive dune.

He adds: “These results will likely surprise a lot of people, as we can see how quickly these enormous sand dunes form, and that they move across the desert at a speed of about 50 cm per year.”

Scientists used a technique called scintillation dating to determine the age of the star dunes.

This method calculates the last time the sand grains were exposed to daylight.

The sand was sampled in the dark from Morocco and analyzed in the laboratory under dim red light conditions similar to an old photographic workshop.

Professor Dowler describes the mineral grains in the sand as “tiny rechargeable batteries.” They store energy within the crystals that comes from radioactivity in the natural environment.

The longer the sand is buried underground, the more radioactivity it is exposed to and the more energy it accumulates.

When the grains are exposed in the laboratory, they release energy in the form of light and scientists can calculate their age.

“In our dark laboratory, we see light from these sand grains,” says Professor Dowler. “The brighter the light, the older the sediment grains are, and the longer it has been since they were buried.”

Another example of such a huge dune is Star Dune in Colorado, North America, which is the highest sand dune in the United States, reaching a height of 225 meters from base to summit.

Professor Dowler explains that climbing these sand dunes is hard work. “As you climb, you go up two steps and slide down one back. But it's worth it – it's so beautiful from the top,” he says.