Sand dunes are constant fixtures of the desert landscape and are always changing – shaped and swept by the plain winds.
They are great hills or ridges beyond the reach of the ocean’s tides and formed from sand often over thousands of years.
They are found in Africa, Asia, North America and even on Mars, and though they play a vital role in certain environments, experts didn’t know much about them – until now.
That is because secrets hidden within one of the world’s most elusive dunes, the Lala Lallia in Morocco, have finally been revealed.
Through examination, a team has dated the star dune back to 13,000 years ago, promising to reveal crucial information about the Earth’s ancient past.
Star dunes are formed when opposing winds change direction. The significance behind knowing how old they are rests with a better understanding of the climate of the past, according to Professor Geoff Duller at the University of Aberystwyth, who published the research with Professor Charles Bristow at Birkbeck University.
Lala Lallia sits in the Erg Chebbi sand sea in south-east Morocco and stands at a staggering 100m high and 700m wide.
Shortly after it was first created, the dune stopped growing for around 8,000 years but expanded at a sizable rate in the next several thousand years.
Deserts can ordinarily be identified in the Earth’s geological history, though star dunes were absent until now.
Some experts, like Prof Duller, believe this might be because they are so large that researchers didn’t realise they were looking at one distinct dune.
“These findings will probably surprise a lot of people as we can see how quickly this enormous dune formed, and that it is moving across the desert at about 50cm a year,” Prof Duller told the BBC.
Using a technique called luminescence dating – which calculates when the grains of sand were last exposed to daylight — the scientists could work out the dune’s age.
Small samples of sand were taken in the dark from Morocco and analysed in a lab where conditions similar to an old photograph workshop, known as a darkroom, were employed.
Prof Duller said the mineral grains in the sand were like “little rechargeable batteries” as they contain energy sourced from radioactivity in the natural environment.
The longer the sand is buried deep within the dune, the more radioactivity it is exposed to, and so the more energy it acquires.
When the grains were exposed to light in the laboratory, they reacted by releasing energy in light form, offering scientists a window of opportunity to calculate their age.
Prof Duller explained: “In our dark laboratory, we see light from these sand grains. The brighter the light then the older the sediment grains and the longer it is since they’ve been buried.”
