The mysterious ‘star dune’ in the Sahara is on the move

By | March 5, 2024

The desert’s enormous star dunes are mysterious structures. These sand dunes are found in some of the largest in the world modern desertsbut also on the planet Mars And Saturn’s largest moon, Titan. Star dunes are gigantic sand dunes that take their name from the arms of sand and rocks that spread downward from a central peak. When viewed from above, they can look like stars.

Scientists have now determined for the first time the age of one of the oldest stellar dunes on Earth. The Lala Lallia star dune in southeastern Morocco is estimated to have formed 13,000 years ago, according to a study by study published March 4 in the journal Scientific reports.

[Related: The Sahara Desert used to be green and lush. Then humans showed up.]

Star dunes are found in sand seas in Africa, Arabia, China and North America. These are believed to be the tallest dunes in the world, with a star dune in China’s Badain Jaran desert climbing to 984 feet.

Despite being very common today, evidence of star dunes has almost never been found on Earth geological record. The geological record is like a time capsule made up of rock and sediment layers that allow geologists to get a glimpse of what the Earth was like thousands of years ago. The absence of star dunes in rocks has puzzled scientists, because past deserts are a common part of Earth’s geological history, but not the types of dunes. Only one ancient star dune has been uncovered, preserved in sandstone. It dates from about 250 million years ago and was found in present-day Scotland.

Lala Lallia Star Dune in Erg Chebbi, Marokko.  <em>CREDIT: Charlie Bristow</em>” data-src=”https://s.yimg.com/ny/api/res/1.2/i_SAIwjw5_C8MK9Qt0qp8g–/YXBwaWQ9aGlnaGxhbmRlcjt3PTk2MDtoPTcyMA–/https://media.zenfs.com/en/popular_science_109/5b9a117d0247622a93 a4047dbe9b089e”/>  <em><knopklasse=

Lala Lallia Star Dune in Erg Chebbi, Morocco. CREDIT: Charlie Bristow

“This research is really about the missing sand dune – it was a mystery why we couldn’t see them in the geological record,” said Geoff Duller, a geologist and earth scientist at Aberystwyth University in Wales, said in a statement. “Only thanks to new technology can we now begin to unravel their secrets.”

This new study used ground penetrating radar to peer into Lala Lallia’s internal structure. The name means ‘highest sacred point’ in the Berber language and the dune is located in the Erg Chebbi area of ​​the Sahara desertnear the border with Algeria.

Researchers found that the sand pyramid reached its current 70 meters height and 700 meters width as a result of rapid growth over the past millennium as it slowly shifted westward. The oldest parts of the dune are 13,000 years old.

According to the research, the star dune probably formed at the same time as the Younger Dryas event. This was a very abrupt period of global cooling, about 12,900 and 11,600 years ago, and it returned some parts of the planet to Ice Age-like conditions, before a period of rapid warming.

The tests also showed that the dune stopped growing for a period of 8,000 years. Pottery found near the sites shows that people could have lived in the region that was not as arid as it is today. A period of extra rainfall or even an extended monsoon stabilized the dune before a major drought began.

Why is Lala Lallia moving?

The ground-penetrating radar showed the structure of the dune layers and revealed how natural changes in the environment, such as rain and wind, built them up over time. The wind from different directions probably contributed to the formation of the gigantic dunes. Using this structural data, they also determined that the Lala Lallia dune is moving westward at a rate of about 4.5 meters per year. Because the dune was formed by wind from two different directions, a third wind blows from the east, causing the dune to slowly shift westward.

To determine the age of the star dune, the team used luminescence dating techniques to determine when minerals in the sand were last exposed to sunlight. The moment at which the sand itself was formed was not taken into account, but at the moment when it was deposited on the dune.

[Related: World’s oldest known wooden structure pre-dates our species.]

“The quartz grains have the properties of a mini rechargeable battery,” Duller said The guard. “It can store energy it gets from naturally occurring radioactivity. If we take it back to the laboratory, we can make it release that energy. It comes out in the form of light. We can measure that and the brightness tells us when the grain of sand last saw daylight.”

By looking at the amount of energy in the sand grains, researchers were able to determine that it took about 900 years for the Lala Lallia star dune to form. It collects about 6,400 tons of sand annually as the wind blows sand into the desert.

The techniques used in this study could be applied to other sand dunes to tell us more about Earth’s climatic history. Luminescence dating has already been used to determine the the world’s oldest known wooden structure in 2023.

According to co-author and sedimentologist Charlie Bristow of University College London“By using ground-penetrating radar to peer into this star dune, we have been able to show how these immense dunes are formed and develop a new model to help geologists better know what to look for in the rock to identify these amazing desert features.”

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