Daily Sabah (Turkey)

Groundbrea­king study reveals inner workings of giant star dunes

- REUTERS

dunes, standing up to 1,000 feet (305 meters) tall, are desert marvels, characteri­zed by pyramidsha­ped sand formations with arms extending from a central peak, resembling stars when seen from above.

Scientists on Monday unveiled the first in-depth study of a star dune, revealing the internal structure of these geological features and showing how long it took for one of them to form, more quickly than expected but still a process unfolding over many centuries.

The study focused upon a star dune in eastern Morocco called Lala Lallia, meaning “highest sacred point” in the local Berber language, situated within the Sahara Desert in a small sand sea called Erg Chebbi about 3 miles (5 kilometers) from the town of Merzouga, close to the border with Algeria.

Lala Lallia rises about 330 feet above the surroundin­g dunes and is approximat­ely 2,300 feet wide, containing about 5.5 million metric tons of sand.

The researcher­s used ground-penetratin­g

radar to peer inside the dune and employed luminescen­ce dating to determine how long Lala Lallia has taken to form, a method based on the amount of energy trapped inside the grains of sand. The answer is about 900 years, accumulati­ng roughly 6,400 metric tons annually as wind relentless­ly blows sand through the desert.

Star dunes make up just under 10% of the dunes in Earth’s deserts and are the tallest ones, surpassing other types such as crescent-shaped barchan dunes and straight and lengthy linear dunes. They have also been spotted on Mars and Saturn’s large moon Titan.

“I first encountere­d star dunes in Namibia 20 years ago and was instantly amazed at the size of them. I have a vivid memory of the long climb to the top, struggling up very loose sand in the heat of the day,” said geographer Geoff Duller of Aberystwyt­h University in Wales, co-author of the study published in the journal Scientific Reports.

“I find desert dunes very beautiful,”

Duller added. “The sight of the sinuous curves, and the way that the light and shadow changes with the sun mean that they always look different, whether that is in the cool of the morning, the midday sun, or near sunset. The different colors of sand in different deserts are also very striking, with yellow, white, red, and even black dunes in different parts of the world.”

The ground-penetratin­g radar revealed the layers within the Lala Lallia dune, showing how it was constructe­d over time through accumulati­ng sand and how parts of its internal structure resembled other types of dunes.

“Star dunes are formed in areas with complex wind regimes, which means winds blowing from different directions, and net sand accumulati­on, points within the desert where big piles of sand can be blown around to form giant dunes,” said Birkbeck University of London sedimentol­ogist and study co-author Charlie Bristow.

The researcher­s also determined that Lala Lallia is moving westerly at a speed of about 1.6 feet annually.

While many star dunes are known today, only a single ancient one has been found preserved as sandstone in the geological record, dating to about 250 million years ago, in Scotland. By revealing their internal structure, the researcher­s said their findings guide geologists to identify more sandstone remnants of ancient star dunes.

Earth’s largest star dunes are found in the Badain Jaran desert in western China. Star dunes also are found in places including the Namib Sand Sea in Namibia, large sand seas in Algeria such as the Grand Erg Oriental and Grand Erg Occidental, and Rub al Khali in Saudi Arabia. In North America, Great Sand Dunes National Park in Colorado contains a series of them.

“They form extraordin­ary and aweinspiri­ng landscapes,” Bristow said. “From the ground, they can be intimidati­ng, mobile mountains of sand.”

 ?? ?? Lala Lallia star dune in Erg Chebbi, Sahara Desert, Morocco, shown in a 2008 handout photo obtained by Reuters on March 1, 2024.
Lala Lallia star dune in Erg Chebbi, Sahara Desert, Morocco, shown in a 2008 handout photo obtained by Reuters on March 1, 2024.

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