24 Feb 2023
Namibia is a fascinating "country of extremes" with landscapes ranging from savannahs, dusty deserts and high mountain ranges to lush sub-tropical settings along the Okavango and Zambezi Rivers.
The country has the highest wandering sand dunes in the world, like at the tourism hotspot Sossusvlei, but did you know that they are now also regarded among the fastest moving dunes and this since a million years.
Some "racing" dunes in the Sperrgebiet manage to wander a record 83 metres per annum and in a northerly direction, driven by strong southerly and south-westerly winds. This is the fascinating result of recent scientific research after satellite photos of the Namib Desert were analysed.
As if that is not all, another group of scientists revealed in January that sand and dust particles from Namibia literally get "carried away" for thousands of kilometres, as far as the South Pole!
Ground samples from both locations were taken, compared and found to be matching. This helps scientists better understand past climate patterns and future trends.
Namibia's large dune belt abruptly ends at the southern bank of the Kuiseb River near Walvis Bay with a few dunes close to the Atlantic shore line up to Swakopmund the exception.
Researchers from the Desert Research Institute and the US Smithsonian Institution used satellite observations from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite to study the motion of Namibian dunes over an 8 -year period until 2022. They found that the average rate at which the dunes in this area move range from 7 to 32 meters per annum.
Large dunes mostly of the sand sea retained their shape, moving about 9 metres per year, according to the researchers. Some of the smaller dunes were much faster, with some moving as quickly as 83 metres annually.
"The smaller dunes tend to appear and disappear. Tracking dunes with satellite images over years and decades reveals smaller dunes regularly popping up and passing larger crescent-shaped barchan dunes", the recently published scientific report noted.
“This is a very high energy wind regime with strong southerly winds. It is one of the windiest desert regions in the world,” said Nick Lancaster, a dune expert and emeritus research professor at the Desert Research Institute. “As a result, the Sperrgebiet dunes are among the fastest-moving dunes in the world.”
The rapid movement of the dunes is shown in the series of Landsat 8 and 9 images acquired between 2013 and 2022. One image per year was used for the animated image.
The images show a group of half-moon shaped barchan dunes and more linear transverse dunes located in the Sperrgebiet of the southern Namib. "The dunes have migrated northward by several kilometers in recent decades", the report noted.
The movement is caused by sand is blown away (eroded) from the upwind side of the dunes and deposited on the lee (slipface) side. Larger dunes move slower because more sand is eroded than at smaller dunes.
“Knowing how to track dune movement remotely is important because there are places in Peru, Egypt, Qatar, and other countries where migrating barchans can damage infrastructure and crops,” explained study co-author Stephen Scheidt. He is now a researcher at NASA’s Goddard Space Flight Center. “It’s also useful for developing and testing models of how the winds and the atmosphere work on both Mars and Earth.”
So many visitors admiring Namibia's dunes, including the ancient, petrified dunes near the Gondwana Namib Desert Lodge, ask where all the sand comes from, which the winds bring along, almost dail.
The sand is carried by the strong winds mainly from the ancient sand layers at the Orange River, which forms Namibia's southern boundary with South Africa. The Namib Naukluft Park has vast areas towards the coast covered by red sand dunes. According to scientific research, the older the dunes are the more red they become due to iron in the sand particles oxidising.
In 2013, UNESCO declared this area as the Namib Sand Sea. It is the only coastal desert in the world that includes extensive dune fields influenced also by by fog. Covering an area of over three million hectares and a buffer zone of 899,500 hectares, the site is composed of two dune systems, an ancient semi-consolidated one overlain by a younger active one.
Dust particles blown away by strong winds and eroding landscapes in this way can remain in the air and travel long distances. Recently, a team of scientists established that dust particles from Namibia, which were found in ice cores in Antarctica had been deposited there during interglacial periods such as the Holocene, the geological era which began around 12,000 years ago.
The renowned Nature magazine reported in January about this study that dust from the Namibian coast was found in the Atlantic sector of the Southern Ocean and areas of the East Antarctic plateau.
Geomorphologist James King, a professor in the geography department at Université de Montréal in Canada, was part of the research team.
King and his master’s student Amélie Chaput collected sediment samples in four zones along the Namibian coast. Their colleagues travelled to the South Pole to sample ice cores.
Afterwards they performed geochemical and isotopic characterisation of the sediments collected on both continents. They also analysed the chemical composition and properties of the dust and compared the samples form Namibia and the South Pole...
“So we didn’t capture dust in Antarctica, strictly speaking, but more precisely the isotopic signature of African dust,” King was quoted in the magazine.
“The analysis confirmed that Namibia has had a much greater impact than was thought; it is the second or third-largest source of dust in the southern hemisphere after South America.”
The famous east wind, which often blows at the coast during Namibian winter time, plays a major role getting the dust particles into the air.
This fascinating research provides clues to scientists about climate patterns in the southern hemisphere.
So, next time you are climbing sand dunes along the Namibian coast, say a quick "hello and goodbye" to the dust particles in the sand you kick up with your feet as they might take off into the air en route to the Antarctic a few moments later...
Brigitte Weidlich
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