Examining dune formation in the deserts of Australia
Dr Matt Telfer has worked with colleagues to understand more about the Strzelecki and Simpson dunefields
"The best super-computer simulations can model the full aerodynamic interactions of a few thousand grains of sand blowing around, and thatÂÌñ»»ÆÞ™s about a teaspoon full. We need to be working across such a range of scales!"
As a scientist specialising in deserts, AustraliaÂÌñ»»ÆÞ™s an obvious place to turn as it is the driest of the continents (apart from Antarctica!). There are so many aspects of the landscape that are spectacular, but for me, itÂÌñ»»ÆÞ™s the dunefields. Pretty much the whole of the centre of Australia is dominated by a vast whorl of dunes, from the Mallee in the southeast to the Great Sandy desert in the northwest. ThatÂÌñ»»ÆÞ™s an area covering 15 degrees of latitude, and 25 degrees of longitude and almost half of it is covered with dunes.
Researching the desert dunefields
IÂÌñ»»ÆÞ™ve done three main research trips out there, focused mainly on the Strzelecki and Simpson dunefields. In the most recent trip, we took the so-called ÂÌñ»»ÆÞ˜Madigan lineÂÌñ»»ÆÞ™ across the middle of the Simpson desert; 11 days of off-road driving, crossing a little over 900 dunes. We know this, because we kept a tally on the dashboard!
With Australian colleagues, especially Paul Hesse at Macquarie University in Sydney, weÂÌñ»»ÆÞ™ve focussed on two main aspects of the landscape. One is fundamental; we see these amazing patterns in the landscape ÂÌñ»»ÆÞ“ 900 or more dunes, equally spaced, stretching out 100s of kilometres in length, and we know that theyÂÌñ»»ÆÞ™ve been there for hundreds of thousands of years. Each dune may only be about ten metres high, but we still donÂÌñ»»ÆÞ™t properly understand why they form these amazing patterns.
Not the deserts you might expect
The thing that will surprise a lot of people is how green these dunefields are. These are not bare sand for the most part; theyÂÌñ»»ÆÞ™re covered in grasses and shrubs, and we donÂÌñ»»ÆÞ™t properly understand yet how dunes are able to form and persist with all this vegetation around. But itÂÌñ»»ÆÞ™s something we see worldwide, too ÂÌñ»»ÆÞ“ central southern Africa is very similar.
The other line of research relates to this, too, and thatÂÌñ»»ÆÞ™s about how this landscape changes, on timescales ranging from decades to millennia. So weÂÌñ»»ÆÞ™ve cored the dunes to find out how stable they are on long timescales, and also surveyed the changes we see in the vegetation on much shorter timescales.
WeÂÌñ»»ÆÞ™ve seen a lot of vegetation change at a decadal scale; some years, dunes are well vegetated, other years much barer. This was a focus of our work in the Simpson, as we know that when Cecil Madigan pioneered the route we took, back in the 1930s, the dunes were much less vegetated than today. By mapping and surveying the dunes, and the vegetation, weÂÌñ»»ÆÞ™re working on understanding exactly how this happens ÂÌñ»»ÆÞ“ and then we can move towards ÂÌñ»»ÆÞ˜why?ÂÌñ»»ÆÞ™.
Identifying the causes of change
There are likely to be climate change impacts, for sure, and the fact that the dunes are there at all ÂÌñ»»ÆÞ“ despite all the vegetation ÂÌñ»»ÆÞ“ suggests that in the past this landscape has much more barren. ThatÂÌñ»»ÆÞ™s a worry, given what we know of current climate change; could it happen again? But what weÂÌñ»»ÆÞ™ve seen of decadal scale change suggests that itÂÌñ»»ÆÞ™s more complex than a simple change ÂÌñ»»ÆÞ“ the landscape response is not a linear response.
WeÂÌñ»»ÆÞ™ve known for over a hundred years that these vegetated dunefields are evidence of changing climates ÂÌñ»»ÆÞ“ at some point in the distant past, the environment must have been drier, and thereÂÌñ»»ÆÞ™s lots of evidence, especially in Australian dunefields, that the climate mustÂÌñ»»ÆÞ™ve also been wetter at different times. We find soils preserve within the sands. But how these changes occur we know very little about. Are changes quick, or slow? Does it happen everywhere at once? Can we find warning signs that the landscape is destabilizing?
Similar findings on distant shores
WeÂÌñ»»ÆÞ™ve recently been able to tie some of this research into dune patterning into a much wider context. In the Great Sandy desert, the dunes follow big swooping patterns, which is something we donÂÌñ»»ÆÞ™t really see anywhere else in Australia, or further afield, in places like the Kalahari. We were able to show that this is due to a long-dry valley running through the desert; the dunes bend downhill.
About the only other place we see similar patterns, amazingly, is on SaturnÂÌñ»»ÆÞ™s moon Titan, which has the biggest dunefield in the solar system. So from this we can learn something about the topography of another world, which we canÂÌñ»»ÆÞ™t see any other way, just from looking at the patterning of the dunes ÂÌñ»»ÆÞ“ and since NASA has now confirmed an octocopter mission to Titan, finding out where we might get the best landing spots could be really important!
Introducing students to the research
There are so many things we still donÂÌñ»»ÆÞ™t properly understand, and our students have been great in helping to tackle some of these mysteries. For instance, in the northwestern deserts of Australia, the dunes form weird chain-like patterns on their crests. ItÂÌñ»»ÆÞ™s something you donÂÌñ»»ÆÞ™t really see anywhere else in the world. Our final year Desert Environment students are right now mapping these, and comparing the distribution of these ÂÌñ»»ÆÞ˜chain dunesÂÌñ»»ÆÞ™ with other variables, such as vegetation, wind patterns and topography to try and work out why they form here.
"The dunefields we see in many of the worldÂÌñ»»ÆÞ™s desert are perhaps the worldÂÌñ»»ÆÞ™s largest example of organization within a landscape ÂÌñ»»ÆÞ“ hundreds of dunes, which have formed over tens of thousands of years, in beautiful repeating patterns. And yet not only do we know how or why this happens, we know that they can change very rapidly. ThatÂÌñ»»ÆÞ™s the real paradox ÂÌñ»»ÆÞ“ a landscape thousands of miles across, made of grains a quarter of a millimetre across, the surface of which can change in one storm, and yet which has persisted for tens of thousands of years."
In May 2018, Dr Matt Telfer led an international research project which for the first time discovered dunes on Pluto and identified how they were formed
Scientists discover dunes on Pluto
A team of scientists led by academics at ÂÌñ»»ÆÞ have published a landmark study revealing the discovery of dunes on the distant dwarf planet of Pluto. Writing in Science, the international working-group of geographers, physicists and planetary scientists revealed how they had analysed detailed images of the surface, captured in July 2015 by NASAÂÌñ»»ÆÞ™s New Horizons spacecraft. They concluded that the dunes are formed by methane ice grains released into its rarefied atmosphere, which are then transported by its moderate winds.
Dr Matt Telfer, Lecturer in Physical Geography at the University, was the paperÂÌñ»»ÆÞ™s lead author. He said: ÂÌñ»»ÆÞœWe knew that every solar system body with an atmosphere and a solid rocky surface has dunes on it, but we didnÂÌñ»»ÆÞ™t know what weÂÌñ»»ÆÞ™d find on Pluto. It is another piece of the jigsaw in making sense of this diverse and remote body, and gives us a more fundamental understanding of the geological processes which are influencing it.ÂÌñ»»ÆÞ
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