Grains of sand reveal mystery of the age of dunes – 03/04/2024 – Science

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

Stellar dunes —or pyramidal dunes— owe their name to their distinct shapes and can reach hundreds of meters in height.

They are found in Africa, Asia and North America, as well as on Mars — but experts have never been able to establish the time in which they were formed.

Now, research has discovered that the dune called Lala Lallia, in Morocco, was formed 13 thousand years ago.

Star dunes are created when opposite winds change direction.

Understanding the age of these formations helps to understand these winds and unravel the climate of that time, says Professor Geoff Duller, from Aberystwyth University, who published the research with Charles Bristow, from Birkbeck University.

Lala Lallia (the indigenous name Amazigh means highest sacred point) is located in the sand sea of ​​Erg Chebbi in southeastern Morocco. It is one hundred meters high and 700 meters wide.

According to the study authors, after its initial formation, it stopped growing for about 8,000 years and then expanded rapidly in the last few thousand years.

Normally, deserts could be placed in Earth’s geological history, but star dunes were absent until now.

Professor Duller says that this happened because they are so large that experts did not realize that it was a single dune, and not several.

“These discoveries will probably surprise a lot of people, as we can see how quickly this huge dune formed and how it moves across the desert at about 50 centimeters per year,” he adds.

Scientists used a technique called luminescence dating to figure out the age of the star dune.

The method allows you to calculate when grains of sand were last exposed to daylight.

Sand samples were collected at night in Morocco and analyzed in a laboratory under low red light conditions, similar to those in photography developing studios.

Duller describes the mineral grains in the sand as “little rechargeable batteries.” They store the energy captured from environmental radioactivity within crystals.

The longer the sand remains buried underground, the more it will be exposed to radioactivity and the more energy will be accumulated.

When these grains are analyzed in the laboratory, they release energy in the form of light, and scientists are able to calculate their age.

“In our darkroom, we see the light from these grains of sand. The brighter the light, the older the sediment grains are and the more time has passed since they were buried,” says Professor Duller.

Other examples of these enormous dunes include Star Dune in Colorado, the tallest in the United States at 750 feet from base to top.

Climbing these dunes is hard work, explains Professor Duller. “When you go up, it’s two steps up and one back, sliding. But it’s worth it, they’re absolutely beautiful from above,” he says.