Scientists Reveal Secrets of Desert Star Dunes

A view of the Lala Lallia star dune of the Sahara Desert, in Erg Chebbi, Morocco, as seen in an undated handout image from 2008 and obtained by Reuters on March 1, 2024. Charlie Bristow/Handout via REUTERS
A view of the Lala Lallia star dune of the Sahara Desert, in Erg Chebbi, Morocco, as seen in an undated handout image from 2008 and obtained by Reuters on March 1, 2024. Charlie Bristow/Handout via REUTERS
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Scientists Reveal Secrets of Desert Star Dunes

A view of the Lala Lallia star dune of the Sahara Desert, in Erg Chebbi, Morocco, as seen in an undated handout image from 2008 and obtained by Reuters on March 1, 2024. Charlie Bristow/Handout via REUTERS
A view of the Lala Lallia star dune of the Sahara Desert, in Erg Chebbi, Morocco, as seen in an undated handout image from 2008 and obtained by Reuters on March 1, 2024. Charlie Bristow/Handout via REUTERS

They are among the wonders of our deserts: star dunes, the vaguely pyramid-shaped sand formations up to about 1,000 feet (300 meters) tall with arms stretching out from a central peak to give them a star-like appearance when viewed 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 km) from the town of Merzouga, close to the border with Algeria.
Lala Lallia rises about 330 feet (100 meters) above the surrounding dunes and is approximately 2,300 feet (700 meters) wide, containing about 5-1/2 million metric tons of sand.
According to Reuters, he 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 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 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, 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 (0.5 meters) 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 provide a guide for 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 awe-inspiring landscapes," Bristow said. "From the ground they can be intimidating, mobile mountains of sand."



Greece's 'Instagram Island' Santorini nears Saturation Point

Tourists queue as they wait to take a picture from one of the balconies. Aris Oikonomou / AFP
Tourists queue as they wait to take a picture from one of the balconies. Aris Oikonomou / AFP
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Greece's 'Instagram Island' Santorini nears Saturation Point

Tourists queue as they wait to take a picture from one of the balconies. Aris Oikonomou / AFP
Tourists queue as they wait to take a picture from one of the balconies. Aris Oikonomou / AFP

One of the most enduring images of Greece's summer travel brand is the world-famous sunset on Santorini Island, framed by sea-blue church domes on a jagged cliff high above a volcanic caldera.
This scene has inspired millions of fridge magnets, posters, and souvenirs -- and now the queue to reach the viewing spot in the clifftop village of Oia can take more than 20 minutes, said AFP.
Santorini is a key stopover of the Greek cruise experience. But with parts of the island nearing saturation, officials are considering restrictions.
Of the record 32.7 million people who visited Greece last year, around 3.4 million, or one in 10, went to the island of just 15,500 residents.
"We need to set limits if we don't want to sink under overtourism," Santorini mayor Nikos Zorzos told AFP.
"There must not be a single extra bed... whether in the large hotels or Airbnb rentals."
As the sun set behind the horizon in Oia, thousands raised their phones to the sky to capture the moment, followed by scattered applause.
For canny entrepreneurs, the Cycladic island's famous sunset can be a cash cow.
One company advertised more than 50 "flying dresses", which have long flowing trains, for up to 370 euros ($401), on posters around Oia for anyone who wishes to "feel like a Greek goddess" or spruce up selfies.
'Respect Oia'
But elsewhere in Oia's narrow streets, residents have put up signs urging visitors to respect their home.
"RESPECT... It's your holiday... but it's our home," read a purple sign from the Save Oia group.
Shaped by a volcanic eruption 3,600 years ago, Santorini's landscape is "unique", the mayor said, and "should not be harmed by new infrastructure".
Around a fifth of the island is currently occupied by buildings.
At the edge of the cliff, a myriad of swimming pools and jacuzzis highlight Santorini is also a pricey destination.
In 2023, 800 cruise ships brought some 1.3 million passengers, according to the Hellenic Ports Association.
Cruise ships "do a lot of harm to the island", said Chantal Metakides, a Belgian resident of Santorini for 26 years.
"When there are eight or nine ships pumping out smoke, you can see the layer of pollution in the caldera," she said.
Cruise ship limits
In June, Prime Minister Kyriakos Mitsotakis floated the possibility of capping cruise ship arrivals to Greece's most popular islands.
"I think we'll do it next year," he told Bloomberg, noting that Santorini and tourist magnet Mykonos "are clearly suffering".
"There are people spending a lot of money to be on Santorini and they don’t want the island to be swamped," said the pro-business conservative leader, who was re-elected to a second four-year term last year.
In an AFP interview, Tourism Minister Olga Kefalogianni echoed this sentiment and said: "We must set quotas because it's impossible for an island such as Santorini... to have five cruise ships arriving at the same time."
Local officials have set a limit of 8,000 cruise boat passengers per day from next year.
But not all local operators agree.
Antonis Pagonis, head of Santorini's hoteliers association, believes better visitor flow management is part of the solution.
"It is not possible to have (on) a Monday, for example, 20 to 25,000 guests from the cruise ships, and the next day zero," he said.
Pagonis also argued that most of the congestion only affects parts of the island like the capital, Fira.
In the south of the island, the volcanic sand beaches are less crowded, even though it is high season in July.
'I'm in Türkiye
The modern tourism industry has also changed visitor behavior.
"I listened (to) people making a FaceTime call with the family, saying 'I'm in Türkiye," smiled tourist guide Kostas Sakavaras.
"They think that the church over there is a mosque because yesterday they were in Türkiye."
The veteran guide said the average tourist coming to the island has changed.
"Instagram has defined the way people choose the places to visit," he said, explaining everybody wants the perfect Instagram photo to confirm their expectations.