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Scientists have managed to calculate for the first time the age of one of the largest and most complex types of sand dune on Earth, the so-called star dune, which owes its name to its shape similar to that of a star when viewed from above. This type of dune, also called a pyramidal dune, occurs in Africa, Asia and North America, as well as on Mars. But experts had never been able to establish the time in which they formed.

Research published this week in Scientific Report, however, revealed that the Lala Lallia dune, in Morocco, was formed around 13 thousand years ago. Discovering the age of the dune helps to understand the winds and climate at the time of its formation, as explained by Professor Geoff Duller, from Aberystwyth University, in Wales, United Kingdom.

“Star dunes form in areas with very complex wind regimes, which means wind blowing from different directions to form giant dunes in the desert,” explained sediment expert Charlie Bristow of Birkbeck University in London, UK. , co-author of the study.

– Lala Lallia (which in the Amazigh language means “highest sacred point”) is located in Erg Chebbi, in the Sahara desert, in southeastern Morocco.

– The dune is one hundred meters high and seven hundred meters long. According to the new study, shortly after its initial formation, it remained stagnant for about eight thousand years, and expanded rapidly in the last few thousand years.

“This discovery will probably surprise a lot of people, because we can see how quickly this dune formed and how it moves across the desert at a speed of about 50 centimeters per year,” explained Duller.

To determine the age of the dune, scientists used a technique called luminescence dating. The method involves calculating when the grains of sand were last exposed to daylight.

Sand samples were collected and analyzed in a laboratory similar to those used to develop photographs, with little red light. According to Duller, the grains of sand are like “small rechargeable batteries”, storing radioactivity captured from the environment in their crystals.

The longer sand remains buried underground, the more it is exposed to radioactivity. When grains of sand are analyzed in the laboratory, they release energy in the form of light.

“In our darkroom, we see the light from these grains of sand,” Duller explained. “The brighter the light, the longer the grain of sand spent buried and exposed to radiation.”

Climbing dunes is hard work, as Duller recalls: “When you go up, it’s two steps up and one step back. But it’s worth it, they’re absolutely beautiful from above.”

2024-03-30 13:17:31
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