Through The Sandglass

“at the avant-garde of solar”

 

On my 2013 Moroccan trip, we drove through the town of Ouazazate, “the door of the desert” and an old trading outpost that grew under French colonial rule as a garrison town and administrative centre. Its more recent claim to fame is as the country’s largest film studio, playing host to the shooting of scenes for Lawrence of Arabia to Game of Thrones, via Gladiator and Salmon Fishing in the Yemen. As we rolled out of town eastwards, I stopped to absorb the spectacular views of the alluvial fans reaching up towards the high Atlas Mountains, from which storms were rolling down violently into the valley. I thought of flash floods, but I was completely unaware of the area’s plans for a new source of fame – and electricity – the largest concentrated solar power (CSP) plant in the world, the first phase of which, as reported in the Guardian, is due to open shortly.

This is a fascinating mega-project, and “mega” is certainly appropriate: when completed, the four linked plants will generate 580MW of power, cover an area the size of Morocco’s capital , Rabat, and will have cost $9 billion. But they will make a key contribution to the goal of solar providing 14% of the country’s energy needs by 2020, together with the resulting substantial reduction in carbon emissions.

Maha el-Kadiri, a spokeswoman for the Moroccan Agency for Solar Energy (Masen), describes the projects as "at the avant-garde of solar", and the technology is certainly different and cutting-edge. Rather than being based on photovoltaic cells, CSP uses sun-tracking concave mirrors – each of them 12 meters high and numbering 500,000 just for the first phase, Noor-1 – to focus the heat on steel pipes carrying a synthetic heat-transfer solution. The fluid is heated to close to 400 degrees centigrade before transferring that heat to the water of the power-generating turbines. It’s a very different technology from photovoltaics, and is more expensive, but has one significant advantage: the heat can be stored. For Noor-1, the storage capacity (using molten salt, not, as the Guardian article reported, molten sand) will be around three hours, but for later phases this will extend to eight hours. When the project is completed, it will be capable of storage amounting to several thousand MW-hours.

 

Ouarzazate solar plant will create enough electricity to power a million homes once it is finished. Photograph: Graeme Robertson for the Guardian

It will be fascinating to see how this project evolves, and how it can overcome a number of challenges. As the Guardian reports:

The potential for solar power from the desert has been known for decades. In the days after the Chernobyl nuclear accident in 1986 the German particle physicist, Gerhard Knies, calculated that the world’s deserts receive enough energy in a few hours to provide for humanity’s power needs for a whole year.

Of course there is immense power capacity in the planet’s arid lands – just as there is in geothermal and tidal energy. But that’s not the point – there are any number of thorny and currently unanswerable questions:

The challenge though, has been capturing that energy and transporting it to the population centres where it is required.

The Noor project can supply much of Morocco’s internal demand, but it is looking to export electricity and, as the collapse of the Desertec project dramatically demonstrated, this is essentially impossible under today’s conditions. Desertec failed not only through internal wrangling, but also in the face of insurmountable political, legal and regulatory hurdles – the foundation for a power grid and interconnectors linking North African countries is simply not there, and, perhaps more surprisingly, it’s not there in Europe either.

Ahmed Baroudi, manager of Société d’Investissements Energétiques, the national renewable energy investment firm, is quoted as saying that  “We are already involved in high tension transportation lines to cover the full south of Morocco and Mauritania as a first step” and, on an extraordinary scale, both economically and politically, “The [ultimate] objective given by his majesty the king is Mecca.”

And then there are the questions about how much of the surface of the arid ecosystem we are prepared to cover with generating facilities, how much water these projects will ultimately require and what is the life of the installations. But we have to give Morocco a great deal of credit for testing this potential.

Unearthly dunes

Once in a while I enjoy losing myself in the wonders of Martian landscapes. Words just don't seem necessary for this selection from the latest HiRISE images.

[All images courtesy NASA/JPL/University of Arizona and thanks to Lee Allison at Arizona Geology for the heads up on the 122 new NASA images] 

Behold, Cataglyphis bombycina is an hairy ant

In writing The Desert book, I became acutely aware that, as a humble geologist, my knowledge has profound limitations. I am not a biologist, botanist, ecologist  - the “ist” list of deficiencies goes on. However, in needing to try to describe the extraordinary (and often unappreciated) diversity of arid lands and the remarkable adaptations that permit it, I read – and learned – a great deal. I was fascinated to discover that, in terms of the olympics of heat-tolerance, the silver ant of the Sahara is the gold medal-winner – from Chapter 6:

In the Sahara, Cataglyphis bombycina, the silver ant and its cousin, Cataglyphis fortis, are the most heat-tolerant creatures known (except, of course, for some types of microbes).

To forage on the carcasses of the less strong, these ants wait in their nests, preparing heat shock proteins, until the heat of the day becomes intolerable for their predators, and then boldly go about their business with body temperatures up to 50 degrees centigrade and ground temperatures in the 60s. The proteins help protect them, as does their reflective silver colouring, and they move at an amazing speed (the human equivalent of over 400 kilometres per hour) on unusually long legs for an ant, keeping themselves off the searing ground surface. Their extraordinary navigational abilities guide them back to the nest by the shortest route. Even so, the silver ants can only spend twenty minutes outside before they succumb and become food for their colleagues.

 

And now the story of the silver ants’ clever adaptations and capabilities becomes even more extraordinary. Under the title “Staying Cool: Saharan Silver Ants”, the School of Engineering and Applied Science at Columbia University recently issued a press release (written by Holly Evarts) that I will reproduce here in its fascinating entirety:

Nanfang Yu, assistant professor of applied physics at Columbia Engineering, and colleagues from the University of Zürich and the University of Washington, have discovered two key strategies that enable Saharan silver ants to stay cool in one of the hottest terrestrial environments on Earth. Yu’s team is the first to demonstrate that the ants use a coat of uniquely shaped hairs to control electromagnetic waves over an extremely broad range from the solar spectrum (visible and near-infrared) to the thermal radiation spectrum (mid-infrared), and that different physical mechanisms are used in different spectral bands to realize the same biological function of reducing body temperature. Their research, “Saharan silver ants keep cool by combining enhanced optical reflection and radiative heat dissipation,” is published June 18 in Science magazine.

“This is a telling example of how evolution has triggered the adaptation of physical attributes to accomplish a physiological task and ensure survival, in this case to prevent Saharan silver ants from getting overheated,” Yu says. “While there have been many studies of the physical optics of living systems in the ultraviolet and visible range of the spectrum, our understanding of the role of infrared light in their lives is much less advanced. Our study shows that light invisible to the human eye does not necessarily mean that it does not play a crucial role for living organisms.”

The project was initially triggered by wondering whether the ants’ conspicuous silvery coats were important in keeping them cool in blistering heat. Yu’s team found that the answer to this question was much broader once they realized the important role of infrared light. Their discovery that there is a biological solution to a thermoregulatory problem could lead to the development of novel flat optical components that exhibit optimal cooling properties.

“Such biologically inspired cooling surfaces will have high reflectivity in the solar spectrum and high radiative efficiency in the thermal radiation spectrum,” Yu explains. “So this may generate useful applications such as a cooling surface for vehicles, buildings, instruments, and even clothing.”

Saharan silver ants (Cataglyphis bombycina) forage in the Saharan Desert in the full midday sun when surface temperatures reach up to 70°C (158°F), and they must keep their body temperature below their critical thermal maximum of 53.6°C (128.48°F) most of the time. In their wide-ranging foraging journeys, the ants search for corpses of insects and other arthropods that have succumbed to the thermally harsh desert conditions, which they are able to endure more successfully. Being most active during the hottest moment of the day also allows these ants to avoid predatory desert lizards. Researchers have long wondered how these tiny insects (about 10 mm, or 3/8” long) can survive under such thermally extreme and stressful conditions.

Using electron microscopy and ion beam milling, Yu’s group discovered that the ants are covered on the top and sides of their bodies with a coating of uniquely shaped hairs with triangular cross-sections that keep them cool in two ways. These hairs are highly reflective under the visible and near-infrared light, i.e., in the region of maximal solar radiation (the ants run at a speed of up to 0.7 meters per second and look like droplets of mercury on the desert surface). The hairs are also highly emissive in the mid-infrared portion of the electromagnetic spectrum, where they serve as an antireflection layer that enhances the ants’ ability to offload excess heat via thermal radiation, which is emitted from the hot body of the ants to the cold sky. This passive cooling effect works under the full sun whenever the insects are exposed to the clear sky.

“To appreciate the effect of thermal radiation, think of the chilly feeling when you get out of bed in the morning,” says Yu. “Half of the energy loss at that moment is due to thermal radiation since your skin temperature is temporarily much higher than that of the surrounding environment.”

The researchers found that the enhanced reflectivity in the solar spectrum and enhanced thermal radiative efficiency have comparable contributions to reducing the body temperature of silver ants by 5 to 10 degrees compared to if the ants were without the hair cover. “The fact that these silver ants can manipulate electromagnetic waves over such a broad range of spectrum shows us just how complex the function of these seemingly simple biological organs of an insect can be,” observes Norman Nan Shi, lead author of the study and PhD student who works with Yu at Columbia Engineering.

Yu and Shi collaborated on the project with Rüdiger Wehner, professor at the Brain Research Institute, University of Zürich, Switzerland, and Gary Bernard, electrical engineering professor at the University of Washington, Seattle, who are renowned experts in the study of insect physiology and ecology. The Columbia Engineering team designed and conducted all experimental work, including optical and infrared microscopy and spectroscopy experiments, thermodynamic experiments, and computer simulation and modeling. They are currently working on adapting the engineering lessons learned from the study of Saharan silver ants to create flat optical components, or “metasurfaces,” that consist of a planar array of nanophotonic elements and provide designer optical and thermal radiative properties.

Yu and his team plan next to extend their research to other animals and organisms living in extreme environments, trying to learn the strategies these creatures have developed to cope with harsh environmental conditions.

“Animals have evolved diverse strategies to perceive and utilize electromagnetic waves: deep sea fish have eyes that enable them to maneuver and prey in dark waters, butterflies create colors from nanostructures in their wings, honey bees can see and respond to ultraviolet signals, and fireflies use flash communication systems,” Yu adds. “Organs evolved for perceiving or controlling electromagnetic waves often surpass analogous man-made devices in both sophistication and efficiency. Understanding and harnessing natural design concepts deepens our knowledge of complex biological systems and inspires ideas for creating novel technologies.”

The study was supported by the National Science Foundation under the Electronics, Photonics, and Magnetic Devices program (ECCS-1307948) and Physics of Living Systems program(PHY-1411445), and the Air Force Office of Scientific Research (AFOSR) Multidisciplinary Research Program of the University Research Initiative (MURI) program (FA9550-14-1-0389).

[Research was also carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory.]

And note that, once again, we are finding inspiration for new technologies not only from the life of the rainforest but from the desert.

 

[Header image: Bjørn Christian Tørrissen, courtesy of Creative Commons, Attribution-ShareAlike 3.0; other images via Columbia press release materials courtesy of Norman Nan Shi and Nanfang Yu] 

The Missing Sink: Carbon storage in the world’s deserts

Deep-rooted and completely erroneous preconceptions of our planet’s arid lands as sterile bit-players in the great game of the earth’s dynamic systems have long inhibited our scientific enthusiasm for, and understanding of, the desert. We are now beginning to catch up – take, for example, this recent headline from the American Geophysical Union:

The world's deserts may be storing some of the climate-changing carbon dioxide emitted by human activities, a new study suggests. Massive aquifers underneath deserts could hold more carbon than all the plants on land, according to the new research.

As described in a summary of this research on Science Daily:

Humans add carbon dioxide to the atmosphere through fossil fuel combustion and deforestation. About 40 percent of this carbon stays in the atmosphere and roughly 30 percent enters the ocean, according to the University Corporation for Atmospheric Research. Scientists thought the remaining carbon was taken up by plants on land, but measurements show plants don't absorb all of the leftover carbon. Scientists have been searching for a place on land where the additional carbon is being stored--the so-called "missing carbon sink."

The lead author of the report in the AGU publication, Geophysical Research Letters, is Yan Li, a desert biogeochemist with the Chinese Academy of Sciences in Urumqi, Xinjiang; he and his team examined the character of groundwaters in the gigantic closed system of the arid Tarim Basin, and came up with some fascinating – and provocative – results. Runoff waters from the surrounding mountains pick up, as a normal part of the carbon cycle, some CO₂ dissolved from the rocks and soils through which the rivers flow. However, by the time that water ends up in aquifers, the underground reservoirs beneath the desert, it contains substantial amounts of DIC, dissolved inorganic carbon.

Being able to date the carbon, Li and his colleagues could distinguish between old carbon originating from the rivers and very young carbon added to the water as it seeped through the soils of the irrigated oases along the desert margins. These are poor soils, not in themselves sources of much CO₂ - it originates from the respiration of the roots of crops and microbes in the soil. And because these crops are irrigated almost constantly, not only to keep them growing but to wash out the salts that, as in all desert agriculture, accumulate in the soil, most of the CO₂ is transported downward into the groundwater moving out below the desert to be trapped in the deep aquifers. Importantly, because of the salts, these waters are saline and alkaline and the solubility of CO₂ in saline/alkaline water is much higher than in pure or acidic water – the desert groundwater is a very significant CO₂ sink. 

Because of their ability to date the carbon dissolved in the waters, the researchers were able to establish that the levels jumped substantially in historical times as the development of the Silk Road enabled the beginnings of oasis agriculture. Man’s activities – irrigation and over-irrigation – have augmented the efficiency of this carbon sink by, it is estimated, a factor of twelve:

Based on the various rates that carbon entered the desert throughout history, the study's authors estimate 20 billion metric tons (22 billion U.S. tons) of carbon is stored underneath the Tarim Basin desert, dissolved in an aquifer that contains roughly 10 times the amount of water held in the North American Great Lakes.

The study's authors approximate the world's desert aquifers contain roughly 1 trillion metric tons (1 trillion U.S. tons) of carbon--about a quarter more than the amount stored in living plants on land.

And because this is a saline and alkaline aquifer, the water is completely unsuitable for agriculture – it will likely remain below the desert as essentially permanent carbon storage - undoubtedly not the only missing sink, but a hitherto unidentified one. As Li remarks: “The fact that such a huge carbon pool and active sink has been unstudied for so long may simply be because it is remote and hidden under deserts: out of sight, out of mind.”

 

[Image at the head of this post is of agriculture and dunes along the northern edge of the Tarim Basin, Google Earth; diagram of the process of carbon storage from Yan Li, Yu-Gang Wang, R. A. Houghton, Li-Song Tang. Hidden carbon sink beneath desert. Geophysical Research Letters, 2015; DOI:10.1002/2015GL064222]

Desert mayhem – Mad Max “Fury Road”

 

Our planet’s deserts are sweeping landscapes of variety and diversity, human and otherwise. But if you are looking for imagery of the desert as desolate and threatening, then the new Mad Max movie will do the trick – in spades. "Our world is fire and blood" declares one of the characters, and indeed it is, crammed with deranged creatures, bizarre weaponry, and outrageous vehicles (plus diaphanously dressed young women), all of them in virtually non-stop action, most of which, incredibly, is real as opposed to CGI.

My reason for seeing Mad Max – Fury Road was, of course to see the desert and the geology, but the pace and drama of the film made it seriously difficult to focus on the background scenery. That scenery was originally (this film has been a very long time in the making) supposed to be Australian, the locations planned around the outback mining town of Broken Hill. But the desert did not co-operate: rains came and the post-apocalyptic setting was festooned with wildflowers, creating an ambience deemed inappropriate. The whole production then switched to Namibia and the stunning arid landscapes inland from Swakopmund. Stunning locations and stunning film-making (the jury is, however, still out in terms of the environmental consequences).

  

I have to say that I enjoyed this Mad Max immensely – I was looking for entertainment rather than intellectual challenge and it most certainly delivered. Herewith, a few of the items I found particularly entertaining – no spoilers, just screen-grabs taken from the trailers on the movie’s website, plus a little commentary. 

 

The scene of Max emerging from being violently buried in the sand is extraordinary – it begins in such a way that the viewer’s sense of scale is completely lost – what are we looking at? It’s only as Max emerges that we become aware.

 

The mother of all sand/dust-storms, from which, of course, the key characters emerged unscathed – along with their vehicles.

 

And those vehicles are, in many ways, the stars. Huge and malevolent, inventive and monstrous steam-punk cannibalizations of vaguely recognisable trucks and cars with decayed post-apocalyptic industrial kitchen equipment and weaponry – plus music. The “Doof Wagon” is perhaps the most eccentric, a gigantic hurtling stage crammed with amps and sub-woofers, the crazed blind Doof Warrior strapped to the front with bungee cords, his enormous guitar doubling as a flame-thrower.

 

At the back of the Doof Wagon are huge drums, whose crazed players beat out the rhythm of war and violence. Oh, and the makings of a brass band – in the final scene of fire and mayhem as the Doof Wagon comes to a violently disintegrating end, I was delighted, in the lower right of the screen to see a tuba tumbling through the air.

 

Our heroes’ means of transport is the War Rig, fully equipped with a cow-catcher. Although no cows remain on the planet, this comes in handy as a sand-plough to extinguish another raging fire.  

No desert is complete without its salt-pans, quagmires after inundation, and, inevitably the War Rig becomes bogged down in the mud and the gloom. I was reminded of Isabelle Eberhardt’s description of the great salt lakes of Tunisia, the chotts:

treacherous expanses where a thin, apparently dry crust hides unfathomed pits of mud . . . And beneath the motionless crystal of the salty waters there are countless archipelagos of clays and multicoloured rocks, in perpendicular and stratified ledges . . . a labyrinth of deep canals, islets, pitfalls, of deposits of salt and saltpetre . . . a leprous region where all the earth’s secret chemistries are on display in the bright sun . . . An inchoate sadness hangs over this lonely region ‘from which God has withheld his blessing’, a vestige, perhaps, of some forgotten Dead Sea, with nothing to boast of but bitter salt, sterile clay, saltpetre and iodine.

It almost seemed as if Mad Max had employed Eberhardt as a script-writer.

As, once again, all seemed lost in the inchoate sadness and desperation, a lone tree miraculously appears in the mist. The poor tree allows the rig to be winched out of the mire, but at the cost of its own destruction.

 

It makes me wonder whether the true story of the lone Saharan Tree of Tenere, supposedly knocked down by a drunken truck-driver, could possibly be that Mad Max came by…

There is spectacular geology to be seen in the movie, but it does hurtle by at a bewildering rate – as does everything. But it is an incredible and highly-recommended super-charged experience.  

 

Our arid planet

Yet again, thank you NASA. As announced last month, their latest extraordinary earth-monitoring system is in orbit, commissioned and providing data: SMAP, the Soil Moisture Active Passive mission provides a high-resolution view of continuing changes in soil moisture across our world and allows understanding, analysis and planning in an unprecedented and fascinating way.

The map above is one of several already available:

These maps of global soil moisture were created using data from the radiometer instrument on NASA's Soil Moisture Active Passive (SMAP) observatory. Each image is a composite of three days of SMAP radiometer data, centered on April 15, 18 and 22, 2015. The images show the volumetric water content in the top 2 inches (5 centimeters) of soil. Wetter areas are blue and drier areas are yellow. White areas indicate snow, ice or frozen ground.

The soil moisture scale is in cm³/cm³ and demonstrates dramatically the often-forgotten fact that drylands, home to a third of our planet’s population, comprise over 40% of the land area.

As usual, the technology is extraordinary:

For an introductory description of how the radar and radiometer instruments conspire, see http://smap.jpl.nasa.gov/observatory/overview/. The NASA press release summarises the mission and the ways in which the data will be used:

Launched Jan. 31 on a minimum three-year mission, SMAP will help scientists understand links among Earth's water, energy and carbon cycles; reduce uncertainties in predicting climate; and enhance our ability to monitor and predict natural hazards like floods and droughts. SMAP data have additional practical applications, including improved weather forecasting and crop yield predictions.

A first global view of SMAP's flagship product, a combined active-passive soil moisture map with a spatial resolution of 5.6 miles (9 kilometers), is available at:

http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA19337

During SMAP's first three months in orbit, referred to as SMAP's "commissioning" phase, the observatory was first exposed to the space environment, its solar array and reflector boom assembly containing SMAP's 20-foot (6-meter) reflector antenna were deployed, and the antenna and instruments were spun up to their full speed, enabling global measurements every two to three days.

The commissioning phase also was used to ensure that SMAP science data reliably flow from its instruments to science data processing facilities at NASA's Jet Propulsion Laboratory in Pasadena, California, and the agency's Goddard Space Flight Center in Greenbelt, Maryland.

"Fourteen years after the concept for a NASA mission to map global soil moisture was first proposed, SMAP now has formally transitioned to routine science operations," said Kent Kellogg, SMAP project manager at JPL. "SMAP's science team can now begin the important task of calibrating the observatory's science data products to ensure SMAP is meeting its requirements for measurement accuracy."

Together, SMAP's two instruments, which share a common antenna, produce the highest-resolution, most accurate soil moisture maps ever obtained from space. The spacecraft's radar transmits microwave pulses to the ground and measures the strength of the signals that bounce back from Earth, whereas its radiometer measures microwaves that are naturally emitted from Earth's surface.

"SMAP data will eventually reveal how soil moisture conditions are changing over time in response to climate and how this impacts regional water availability," said Dara Entekhabi, SMAP science team leader at the Massachusetts Institute of Technology in Cambridge. "SMAP data will be combined with data from other missions like NASA's Global Precipitation Measurement, Aquarius and Gravity Recovery and Climate Experiment to reveal deeper insights into how the water cycle is evolving at global and regional scales."

It is, to me, wondrous that even a simple examination of the three successive images from which the one at the head of this post was taken reveals clear changes over the course of a few days – I can only begin to imagine what analysis of the real data will reveal.

The UN’s map and classification of global drylands drives home their importance to the way our planet works. The new SMAP data bring this to life in a dramatic way.

  

[SMAP image credit: NASA/JPL-Caltech/GSFC] 

New book review by Andrew Goudie

Well, sometimes you just have to throw modesty to the dusty winds and shamelessly take on a little self-promotion. The desert book was just reviewed for The Geological Society by Andrew Goudie, Emeritus Professor in Geography at Oxford, a leading international authority on arid lands. The review is available online (it will be published in Geoscientist in a couple of months), but here it is:

This handsome book is informative, well-illustrated, broad-ranging, and clever. The author, a geologist and professional writer, who in 2009 wrote a well-received book, ‘Sand: A Journey through Science and the Imagination’, has managed to weave together a whole array of different strands that serve to make deserts what they are. 

Using some of his own field experiences, coupled with a wide reading of the literature, he has succeeded in covering the science of deserts (including climate, geomorphology, and wildlife), while at the same time discussing the human inhabitants of deserts, art and literature, and some of the arresting characters who risked their lives in discovering and traversing the world’s dryands.

It aims, as the author explains, to ‘provide an evocation, a celebration, a consideration of our response to the desert, the idea of the desert’, for ‘deserts are landscapes of the mind as much as physical realities, places of metaphor and myth.’ Using examples from central Australia, the Namib, the Gobi, the Sahara, the Mojave and the Atacama, it examines such landscapes in the context of their place in history, as birthplaces of civilizations, evolutionary adaptations, art, ideology and philosophy. To be sure, it does not cover everything relating to this vast topic, but it provides a superb introduction to what makes deserts so fascinating and alluring.

To give an example of how different material is cleverly combined, consider his treatment of flash floods. The climatic and geomorphological conditions that produce them are described, there are some graphic descriptions from the literature, but there is also a description of an explorer who was killed by a flash flood in the Algerian Sahara, Isabelle Eberhardt. We learn that she probably had syphilis, was illegitimate, was a habitual user of drugs, was highly promiscuous, and cut her hair like a man.

Equally, some pervasive surface features - stone pavements - are explained scientifically, but are also placed in the context of the disturbance of desert surfaces in the Libyan Deserts by the narrow tyres of the Model T Fords used by great desert explorers like Ralph Alger Bagnold. Similarly, dust storms are introduced by a consideration of the life and writings of Mildred Cable and her colleagues in the Gobi, but this is followed seamlessly by a discussion of how the global importance of dust storms has been revealed by the latest satellite-borne sensors.

Lovers of deserts will love this book and will also learn much from it.

Reviewed by Andrew Goudie, University of Oxford.

 

[Image from NASA: A dust storm was blowing large quantities of dust out over the Persian Gulf and Arabian Sea on Saturday, December 13, 2003. In this true-color composite scene, acquired by the Terra and AquaModerate Resolution Imaging Spectroradiometer (MODIS) instruments, the dust storm (light brown pixels) can be seen extending from the Arabian Peninsula (left) eastward over the Persian Gulf and the Gulf of Oman toward the Arabian Sea. Parts of southern Afghanistan and much of Pakistan are also covered by airborne dust.]

The desert and the Large Hadron Collider

 

The possibilities surrounding the re-start of the Large Hadron Collider are endless, but what, of course, intrigued me in a recent piece in the New Scientist was the imagery of the desert. One of the aspirations for my book was to explore the many roles of the words “the desert” in our imaginations, and here they are as we continue our journey to unravel the secrets of life, the universe and all that.

The article begins:

THEY call it "the desert" – a vast, empty landscape separating us from a promised land that shimmers like a mirage on the horizon. A land full of answers, where we finally achieve a complete understanding of material reality.

Stop dreaming: we can't get to this nirvana. The way across the desert is too long and hot, and we have no vehicle to take us there. But if physicists' hopes are realised, a machine just waking from a two-year slumber could bring us a decisive step closer – and might even reveal answers closer to home…

Since February 2013, the LHC has been undergoing a comprehensive overhaul. Now it is gearing up again, more powerful than ever before, for a journey towards the desert – and the complete unknown. The excitement is palpable. "We are living in a once-in-a-lifetime experience, opening the curtains on a totally new energy scale," says Jim Olsen of the LHC's CMS experiment.

…

For most physicists, the conclusion is that the standard model is part of a bigger theory – one that brings us closer to unifying all forces and understanding matter at all energy scales. The problem is, although precise predictions vary, our best guess is that further bouts of force unification only lie at scales of trillions of TeV and above, that were last attained in the first trice of the universe – within 10^-36 seconds of the big bang.

No accelerator on Earth could conceivably achieve such energies. In this picture, what lies between us and the unattainable promised land is a desert devoid of interest. It makes the LHC's upgraded collision energy of 13 TeV seem a rather forlorn gesture.

Not so, says theorist Ben Allanach of the University of Cambridge. If the favourite candidate for a next-generation theory is right, the sliver of new territory we are about to enter could contain particles and phenomena that will take us a decisive step closer to an ultimate answer.

The theory in question is supersymmetry, or SUSY to its friends.

… gravity's true strength might be such that the promised land of unification lies at energies much closer to where we are now, perhaps even within the LHC's reach. Then the desert would be no desert, but full of a host of strange objects such as miniature black holes, which the LHC might be able to squeeze into existence by warping and pinching space-time in its collisions.

…

So the hope is that the territory about to be explored is a lush forest bristling with particles that give us clues to the nature of the desert – and beyond.

  

Georgia Tech Crab Lab: guest post on the art of sidewinding

Over the life of this blog, I have written a number of times on the remarkable and innovative work carried out at Georgia Tech’s Crab Lab, investigations into how critters get around in loose sand and how this can be applied to robotics (see, for example, here, here, and here). Crab Lab is headed up by Dan Goldman, and I was recently delighted (and flattered) that he contacted me about the “Sand” book. I asked if he and his colleagues would be willing to contribute a guest post – and here it is. Courtesy of Henry Astley, a postdoc “who loves all things snakes” and collaborator Joe Mendelson: the state of the art on the physics of sidewinding.

 

In spite of their barren reputation, deserts around the world teem with life, including a wide array of animals from beetles to camels. While much has been written about their adaptations to deal with two of the most notable characteristics of deserts, extreme temperatures and scarce water, far less attention has been paid to their interactions with the other distinguishing characteristic of many deserts: sand.

The ability to move from place to place is crucial for animals to find mates and resources, regulate their body processes, avoid predators, and colonize new environments. But sand makes locomotion difficult, whether moving on it or through it. Particularly problematic is that sand will behave as a solid under certain loads, but will yield and flow like a fluid under others, and very small differences in foot placement and movement can be the difference between moving and becoming hopelessly stuck. Animals deal with this challenging substrate in a variety of ways, whether by anatomical changes or selecting the best movement patterns.

Perhaps the strangest movement pattern of desert animals is the famous “sidewinding” locomotion, seen in certain snakes of sandy deserts around the world. While prominent herpetologist Clifford H. Pope wrote in 1955 “A study of [sidewinding] is recommended to anyone who likes to be confused,”, the underlying motion is quite clear when examined in detail. The snake lifts its head and moves it forward, placing it on the ground, then repeats this motion in a propagating wave down the body – see Science paper supplementary movies.

This produces a characteristic trackway consisting of a series of parallel lines, with the imprint of each scale on the belly clearly visible, showing that the snake does not slip (which would smear the tracks and erase the fine scale imprints). Ultimately, this seemingly complex motion can be reduced to a pair of waves producing vertical and horizontal body undulation, +- 90 degrees out of phase, which propagate together down the body. This simple model may be a “neuromechanical template”, a simple model of a motion which captures all the essential features, potentially serving a simple “target” for the animals to control their locomotion (see Sidewinding with minimal slip: Snake and robot ascent of sandy slopes). This two-wave template of sidewinding also produces sidewinding locomotion when applied to a snake robot, allowing the robot to move on sand effectively.

 

 Screen-grab from Science supplementary movies

This provides a great experimental tool, because the physics of sand have yet to be reduced to simple systems of equations (as has been the case in fluids for almost 200 years), making computer modeling of results difficult and time-consuming. However, the snake robot provides a “physical model” for movement in sand, allowing us to test hypothesized biological mechanisms. Further observations of biological snakes have revealed the modifications of the two-wave template responsible for effectively sidewinding up inclines and turning (see the recent PNAS paper), which in turn have further improved the effectiveness of the robot.

In spite of these insights, the serpents of the sand still hold many mysteries. Why do some snakes sidewind, while others don’t? Why can some species move effectively on sand, while others fail? How do sidewinders deal with obstacles? Can we reconstruct the evolution of this remarkable mode of locomotion from the tracks it has left, or has this history been lost in the sands of time? 

[My sincere thanks to all at Crab Lab for their work and this post. Photographs by Henry Astley]

On the Edge of the Sahara: a guest post by Ann Lingard

At the edge of the Sahara, I stood for a while and watched a dune move. It pushed out its toes, testing the flat ground in front of it; a small trickle of sand cascaded down the lee side and staked a claim, a first footstep of a few millimetres, across the stony flat.

We were in south-east Morocco, and had spent much of that morning crossing the reg, a gravel plain, and were now into the erg, a broad sea of dune-waves. It was a windy day, the sky hazy with particles and the ground beneath our feet blurred by a spray of sand. The particles whipped round our calves as we tramped up each windward slope. From each crest – the sharply-carved edges so familiar from tv documentaries and photos – there would be a view of more dunes; and then we would stride down the lee side where the negative pressure, created as the wind skimmed above our heads, sucked the disturbed sand upwards into our faces.

Having long ago read Michael’s book Sand, and having skimmed the relevant sections in The Desert (his new book arrived two days before our flight), I was delighted to experience for myself the physics and lexicon of dune-formation (saltation, reptation – lovely words): to watch the bounding sand-grains knocking into each other, leaping in the air, and co-operating to form small avalanches; to see the different patterns of aeolian ripples - and to draw comparisons with water-formed ripples on my home patch, the Solway shore.

Less delightful was the determined ingress of sand grains into clothes, socks, boots, eyes, hair and later, food (but no ‘sand in the sandwiches’ here – much tastier ‘sand in the salad’ and tagine instead).

And then, after about four hours’ walking, we came to an area of flat ground on which the dunes were scattered, not contiguous, encroaching individually or in small groups. Formerly this had been the bed of a lake, on the flood-plain of the River Draa, but after the dam was built upstream near the Atlas mountains and the river’s path moved for irrigation purposes, the lake inevitably dried out, leaving a stone-scattered and gently-contoured plain. Now, the sand was taking advantage of this empty space and was piling up and moving in, millimetre by millimetre.

However, it wasn’t only the dunes that were intriguing, for whenever we came to areas of reg, the flat and stony desert, there were scatterings of red or grey clay potsherds – handles, fragments of bowls, even a couple of large, almost-whole pots. Some pieces were engraved with simple patterns, and a few had remnants of green glaze. Had these fragments been washed down from dwellings in the Atlas or the Draa Valley? How old were they? Sadly, other than a comment that they were ‘perhaps a hundred years old’ it wasn’t possible to get a definitive answer from our Berber guide.

The camels, carrying three days’ water, the food, cooker and utensils, and our tents and baggage, moved faster than we did, and one of the camel-drivers had staked a sack on top of a ridge to show exactly where that night’s camp was being pitched. The camp-site, on flat ground between the tall dunes of Zahar, felt remote, yet without the use of GPS or compass, our guide had led us to this spot.

The next morning, an hour after we had set off, a lightly-laden camel and his driver suddenly appeared from between the dunes and crossed our path, following an unseen (to us) route. Elsewhere we saw camel footsteps imprinted and dried into what had once been mud. Humans and their animals were moving purposefully through this landscape, clearly using natural signs and age-old knowledge. Lacking this knowledge, and with only the footprints of other members of our party to follow, we would soon have been lost.

But not all the footprints were caused by human-related passage: parallel scrapes of the clawed feet of laboriously-moving beetles; a lizard’s skittering footsteps straddling the straight line of its tail; small mammalian footprints – gerbils, scampering and churning the sand around their burrows; and the focussed, straight-line padding of a fox: apart from these signs, no-one would have known that animals were living in this landscape.

After four days trekking through erg and reg, wadis and hamada, and feeling the chill of February nights that were deeply silent except for the occasional camel grumbling, and seeing into the depths of the Milky Way, I came away with a sense of wonder at what I had seen – but also knowing that, apart from saltation and reptation, I really didn’t understand a thing.

  

Sunrise at the well of Tilhatine

 

[Ann is an old friend of mine and of the Solway Firth, a sheep-raiser and weaver – and a wonderful writer. Enjoy Solway Shore Stories, her blog, Solway Shore-walker, and her extraordinary and compelling novel, The Embalmer’s Book of Recipes, now out in its second edition. See also Ann’s website. Since she has recently been trekking in the Moroccan desert, I requested a guest post – and here it is, so many thanks, Ann.]