Mystery behind one of Earth’s oldest star sand dunes revealed

Researchers estimate age of star dune called Lala Lallia, Morocco

Scientists have calculated the age of one of the Earth’s oldest dunes for the first time, an advance that could shed more light on climate and wind conditions thousands of years ago.

Star dunes are the tallest and most complex type of desert sand formations, reaching hundreds of meters in height.

They are named so due to their pyramidal form and radiating arms and are widespread in deserts including the sand seas of Africa, Arabia, China, and North America, as well as on Mars and Saturn’s moon Titan.

Star dunes are created by opposing winds changing direction but they have previously not been dated.

Now, researchers have estimated for the first time the age of one such star dune called Lala Lallia in Morocco.

They found that the star dune formed 13,000 years ago in the Erg Chebbi sand sea in southeast Morocco, now reaching about 100 m high and 700m wide.

Scientists found that the sands have grown rapidly within the past 1000 years, which is migrating towards the west.

The latest findings, according to researchers, support the theory that the star dune’s formation was accompanied by a change in wind directions over the years.

The study could enable the identification of star dunes in future studies of the rock record.

Researchers estimated that the 100 m tall dune likely stopped growing for about 8,000 years, and then expanded quickly in the following several thousand years.

This period when the dune stopped growing is marked by scattered pottery fragments to the east side of the sand formation.

This suggests there may have been wetter conditions when the dune was likely to have been stabilised by vegetation.

The findings also raise questions about how such a tall dune formed and kept moving at about 50cm each year.

In the study, scientists used a new technique to date the dines in which they estimated when grains of sand were last exposed to daylight.

The sand grains tend to absorb radiation from their surroundings which they release in the lab under specific conditions.

If they remain buried for longer periods, they absorb more radiation, helping create a timeline of the layers of sand.

The brighter the glow from some grains, the older they are.

Using this, researchers could assess the energy different layers released to calculate their age.

“At the base of the dune, there is an ~ 8000-year hiatus in the record. Since then, the dune has grown rapidly to create a 100 m high dune within the past 1000 years and is migrating towards the west,” scientists wrote in the study.