Towering star-shaped sand dunes in the desert New research finds that the desert formed in less than a thousand years.
The study was published March 4 in the journal Scientific reports, is one of the relatively few that can be viewed from the so-called star dunes, which are the tallest sand dunes on Earth. Star dunes are named for their multi-armed shapes, and they form in places where the wind changes direction throughout the year, according to National Park Service.
Although star dunes are found all over the world, there is only one confirmed star dune in the rock record, from about 250 million years ago in Scotland. Charles BristowAn emeritus professor of sedimentology at University College London told Live Science. This may be because researchers don't know what to look for to identify ancient star dunes, he said.
These dunes are difficult to study because they are usually in remote locations, and accessing a few hundred feet of shifting sand is not easy.
Sand dunes are found in Morocco in a dune field called Erg Chebbi. Fortunately for researchers, the area has become a popular tourist stop, so there are good roads and hotels around the edges of the dune field.
The dune itself is about 330 feet (100 m) high. It is known as Lala Lala by the locals.
To collect data on the dunes, Bristow, a co-author of the study Jeff Doler Researchers from Aberystwyth University and research students used ground-penetrating radar, which can detect small differences in sand grain sizes and water content beneath the surface of a dune. This technique allowed researchers to build a picture of the inner layers of the sand dunes.
They also dug trenches to take samples of long-buried sand. Quartz in sand accumulates radiation from natural sources within the Earth as it is buried. By shining a laser on quartz, researchers can measure this radiation and determine when sand was last seen on the surface.
This look inside the dunes revealed a surprisingly short history. “The most notable thing is how young she is,” Bristow said. “We expected that a 100-meter-high sand dune would be very old… thousands of years, maybe tens of thousands of years. This sand dune turned out to be 900 years old.”
The sand near the base of the dune was buried about 12,000 to 13,000 years ago. Bristow said these represent ancient sand dunes in the area. Shortly after these ancient dunes became active, there came a period of 8,000 years in which sand did not accumulate. The first part of this quiet period coincided with the shift toward a warm, humid climate in the Sahara around 11,700 years ago, marking the end of the Pliocene. The last ice age And the beginning of the Holocene.
“The desert has gone green,” Bristow said. Plants sprouted, settling the sand, and humans wandered the swampy environment, perhaps in search of food. Pottery shards and stone tools were found on one side of the Lala Lala dunes.
About 4,000 years ago, this wet period ended and the desert dried up again. Bristow said the dunes did not start forming immediately. There may have been a lag when sand blew but did not accumulate, or when dunes began to accumulate elsewhere.
The researchers found that Lala Lala moves about 1.6 feet (0.5 metres) every year.
The team found that stellar dunes only started growing within the past 900 years or so.
Bristow said the results suggest that although there may be star dunes trapped in sandstones around the world, they are difficult to detect. Because the dunes are so massive and lack a single distinguishing feature, researchers would need large, exposed layers of rock to get a wide enough view to identify the star dunes. However, in some places, it may be possible to make those definitions.
“It's a collection of features that actually look like other dunes, but if you put them together, you can say, 'Ah, this could be a star dune,'” Bristow said.
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