They are among the wonders of our deserts: star dunes, the vaguely pyramid-shaped sand formations up to more than 300 metres tall with arms stretching out from a central peak to give them a star-like appearance when viewed from above.
Scientists yesterday 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 5km from the town of Merzouga, close to the border with Algeria.
Lala Lallia rises about 100m above the surrounding dunes and is approximately 700m wide, containing about 5-1/2 million metric tonnes 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: about 900 years, accumulating roughly 6,400 metric tonnes annually as wind relentlessly blows sand through the desert.
Star dunes make up just under 10 per cent 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 also have been spotted on Mars and on 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, in a the study published in Scientific Reports.
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