The Simpson, part of deserts stretching 2000 km

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By MIKE GILLAM

From Alice Springs (545m elevation) to Lake Eyre at (90m below sea level), remains of the fallen mark the roadside especially during periods of drought. I stop to photograph one such carcass. A yellow ear tag helps to animate the desiccated cow, almost frolicking through the yellow flowering Sennas of the afterlife, a case of art distorting the very likely hard death it suffered.

The arid zone setting at old Andado is comparatively lightly grazed and much of the surrounding erg or dune sea holds little interest for cattle. Drilling programs from the 1960’s accessed artesian water and an array of man-made dams and tanks were strategically placed but time and grazing have not completely subjugated this desert’s vigour or vastness.

Comprised of aeolian sand Simpson Desert (Munga-Thirri) is an erg, that is a sand sea or dune sea formed during extended periods of aridity. Viewed from satellites it’s clear that the distinctive parallel alignment of the Simpson Desert dunes are part of an anti-clockwise continental whorl shaped by prevailing winds over many thousands of years. Core samples have revealed dates reaching back 600,000 years with a notable period of dune building at 20,000 years before present day.

Steve Morton summarises the dune building events of the late Pleistocene: “Dunes first began forming 70,000 years ago and stabilised in the interglacial phases (when climate was characterised by higher temperatures and moisture) as greater plant growth mitigated the wind’s power. The dunes are striking reminders of the inconsistency of climate, most recently moving across the cold terrain 10,000 years ago but now barely active.”

While the bright red dune crests are often windswept, the flanks are well vegetated. Zygochloa (cane grass) dominates with low hardy shrubs such as Thryptomene and taller Acacias and Sennas, interspersed across a delicate and fabulous mosaic of native annuals that peak after rain. Certainly, this sand ridge desert does not compare to the visual standards set by the starkly bare ergs that occur in the Sahara. The dunes of the Simpson attain a maximum height of some 90’ (30m) whereas the more mobile dunes of the Sahara reach a staggering 300’ (100m).

There are some similarities in the geological description of both but the percentages of area differ greatly. Principal landforms of the Sahara desert shares certain characteristics with the Simpson, and like the Simpson there is a spectrum of land forms more or less vegetated, ergs (dune desert), regs (stony desert), hamadas (mesas).

Indeed the Saharan dunes that dominate our imagination, also obscure a reality that regs (stony plains) comprise 70% of this geographically defined area.

Perhaps the Simpson Desert more closely resembles the Kalahari: “The first thing that strikes you about the Australian deserts is their continental scale: from east to west, more than 2,000 kilometres across. Collectively, they form the largest arid region in the southern hemisphere, covering some three to five million square kilometres of desert uplands, stony desert, sand plain, and dune-fields: about 70% of the Australian landmass. Like the Kalahari, these deserts are well vegetated and only moderately arid.” Mike Smith and Paul Hesse in 23 deg. S. Archaeology and Environmental history of the southern deserts (2005).

Transformation of the Sahara from a vegetated mosaic that once attracted elephants, to a hyper arid desert was triggered by changes in the tilt of the earth’s axis. “Climate scientist Gavin Schmidt, of NASA’s Goddard Institute for Space Studies, explained that around 8,000 years ago, the tilt of the Earth’s orbit changed from around 24.1 degrees to the present day 23.5 degrees … The changes in the Earth’s orbital tilt and precession (or the wobbling motion) occur because of gravitational forces emanating from other bodies in our solar system.”

“This tilt changes between roughly 22 and 25 degrees … every 41,000 years … recent research is suggesting that the effects of global warming – particularly the oceans – could cause a change in the Earth’s axial tilt. Scientists from NASA’s jet Propulsion Laboratory say that the current melting of ice in Greenland is already causing the tilt to change at a rate of approximately 2.6 centimetres each year. They predict this change could increase in the years ahead. Given the very strong dependence of vegetation on water availability, the end of the “Green Sahara” came about quite suddenly around 5,500 years ago. Thus a very slow change in the orbit (led) to an abrupt collapse in that ecosystem.”

Coincidentally or as a consequence of dwindling game, the region’s hunter gatherers turned progressively to animal husbandry and land use impacts such as over grazing by goats and cattle are implicated in desertification and the nature of the Sahara we know today. There is much speculation, conjecture and debate concerning the processes at work in the Saharan landscape. Single cause and effect is possible but a combination of factors seems more likely.

In a reversal of climate change fortunes, some scientists are predicting that climate change may even result in a “greening” of the Sahara, ushering in an age when a preponderance of losers will surely outnumber the world’s winners.

A world away, in Alice Springs, there are predictions of temperature rises assuaged by possible increases in frequency and intensity of rainfall, courtesy of the subtropical monsoon. My friend, Botanist ecologist, Peter Latz, predicts the likely rise of “woody weeds”, native Acacia’s for the most part, as shrubs take advantage of the elevated carbon in the atmosphere and replace stressed grasslands.

In Australia, maintaining the cliché of wind sculpted desert dunes is a long standing obsession of professional image makers despite the obvious difficulties and an overwhelming body of contradictory evidence.

Marketers, publishers and documentary film-makers have invested many decades striving to achieve the Saharan ideal for desert landscapes in Australia. In his landmark 2022 book, Australian Deserts, ecologist Steve Morton recounts a conversation with a film director, jubilant after securing his prized footage, a desert sequence finally made possible after the film crew removed all the vegetation from a Centralian dune to match the expectations of their intended and unsuspecting audience.

Like most photographers who are drawn to Munga-Thirri I have wandered the tallest dunes and studied red crests looking for graphic images, though more in the style of Death Valley than Namibia.

It’s amazing what you can do with a wide angle lens to expand the apparent size of sculpted features and the textured patterning of rippled sand but Sahara it is not. The most barren dunes in my experience are the crescent or horse-shoe dunes associated with the ancestral flows of the Finke River.

Recalling a time when the river ran wider and deeper, wind and floods over the aeons have transported the finest sands from the old palaeo-channels and thrown these up to form perched dunes well above and beyond the influence of active river channels and wetlands.

Depending on the light, these crescent dunes are pale yellow or cream and support very little vegetation though it must be said they occupy relatively small areas, measured in tens of hectares rather than square kilometres. Similar situations on a larger scale occur in Western Australia (eg. Eucla and Ooldea) where highly mobile dunes even threaten local infrastructure such as roads. Some examples are about geography and others a combination of factors including destructive land uses and erosion.

Much of the perennial vegetative mantle of Munga-Thirri while impressive in biodiversity and biomass is of little value to pastoralists intent on the traditional grazing of livestock. In good seasons, desert annuals enhance native pastures but availability to grazing stock is the exception rather than the norm and the vagaries of weather are an unforgiving and difficult host.

Feral camel herds with their capacity to subsist on minimal water and graze taller shrubs and trees are rapidly multiplying and pose a threat to the future of these de-facto wilderness regions.

Infertile soils and low rainfall are undoubtedly the greatest assets of Australia’s arid regions simply because these “deficiencies” mostly lock out big agriculture, in the form of intensive grazing and with it, widespread land clearing and degradation.

These natural defences also provide some protection against weeds and are further enhanced in the Tanami, Gibson and Great Victoria deserts where the unpalatability of spinifex is a saviour of inland Australia, much of it virtually unmanaged wilderness and existing outside the protections of the conservation estate. More recently the declaration of Indigenous Protected Areas have stepped into this management void and in the process offered ranger jobs in regions where employment options are sparse.

These great deserts, long considered self-protecting by virtue of comparative isolation and a low density of humans are facing expanding threats from feral animals such as camels, invasive buffel grass and the fracking ambitions of mining companies that threaten aquifers and water dependent ecosystems.

Wildfires that sweep across the country are perhaps the most serious threat, one that can only be remedied through greater investment in mosaic burning as practiced traditionally by Aboriginal people and now a more likely scenario that includes the aerial deployment of incendiaries at optimal times.

The light aircraft approached old Andado in the late afternoon. The parallel dunes were boldly defined with low angled light casting wide and deep shadows on the opposite side to the setting sun. A linear cloud lies parallel to the horizon. A breath-taking view of Munga Thirri.

9 COMMENTS

  1. Brilliant. Fascinating. Evocative. Instructive. Thanks again Mike. Too long absent from these edifying pages.

  2. Thanks for readers’ kind words.
    I forgot to mention the presence of significant areas of Mitchell grass on heavier clay soils that are valued by pastoralists.

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