Through The Sandglass

Bubbles and grains of sand

Having returned from exhorting my geoscientific colleagues to converse with the physicists who are exploring the bizarre behaviours of granular materials, I am now endeavouring (hopelessly) to catch up on the piles of journals and magazines that were awaiting me in London. I have just been perusing the April editions of the New Scientist, and came upon the following short report, titled “Bubbles exhibit weird sandy behaviour”:

A SQUIRT of bubbles can act like a liquid or a solid depending on its density - a feat thought unique to grainy materials such as sand.

Pour sand, seeds or powder down a chute and they can flow like a liquid. But if the grains are packed so that they fill 64 per cent or more of the chute, they jam up and behave like a solid. The grains are thought to start moving with their neighbours, forming temporary "necklaces" that resist flow, although it is unclear why the transition occurs at this point.

To investigate whether bubbles behave in a similar way, Rémi Lespiat and his colleagues at the University of Paris-East in France squirted nitrogen gas into a chamber of water and monitored the resulting bubbles' passage through a tube.

At low densities, the bubbles flowed. But when they filled 64 per cent of the tube, they jammed just like the grains (Physical Review Letters, DOI: 10.1103/PhysRevLett.106.148302). The result suggests there may be a universal rule that kicks in when objects fill 64 per cent of a space.

"It's surprising that they get the same figure," says Randall Kamien at the University of Pennsylvania in Philadelphia. He suggests using the insight to evenly mix bubbles of gases for medical applications.

My exhortations in Milan included references to the phenomenon of jamming, the analogies between jammed materials (such as glass), and traffic flow (living in Jakarta this has particular resonance), and, for that particular audience, the poorly understood behaviour of sand in their well-bores. The reference in the New Scientist piece to “necklaces” reminded me of an illustration that I had used in my talk – the bridging (and therefore jamming) of granular materials as they flow through an orifice (think, for example, of an ineffectively designed sandglass). Thanks to the wonders of the ability of photo-elastic materials to show us the distribution of stress (and the formation of “force chains”) during flow through a chute (and thanks to the researchers at Duke University who revealed this), the illustration at the head of this post shows exactly such a necklace, bridging and jamming flow.

And now it seems that bubbles do exactly the same thing – what a strange and wonderful world we live in.

Sand, steam, and slowing down - serendipity in Milan

 
On the opening night of the AAPG International Conference in Milan, I was lucky enough to be invited for a guided tour of the Museo Nazionale della Scienza e della Tecnologia "Leonardo da Vinci," followed by dinner in the part of the museum that was once an old priory. It was an altogether enjoyable experience, and one that started off with one of those odd, random, and entertaining convergences. The first stop on our tour was the transport hall, a cavernous space filled with diverse means of locomotion, and we spent a while examining a serious piece of engineering in some detail – steam locomotive 691-022, built in 1914, and retired from the Milan to Bologna route. It of course caused nostalgic conversations amongst those of us of a certain age, the personal archives of sight, sound, and smell being stimulated and re-lived.

Towards the end of his description of this leviathan, our guide posed a question: “given the lack of friction between the wheels and the track, how was the monumental momentum of this locomotive countered when trying to bring the thing to a halt?” Rather modest brake shoes were observed, but it was agreed that they would be quite ineffectual since the whole thing would simply continue to slide. It was, inevitably, yours truly who felt compelled to shout out “sand!” The dome on the top of the boiler (visible in the photos above) was the sand box from which a pipe can be seen leading downwards to feed the sand onto the track. Of course, yours truly had failed to bring a camera for the occasion, but here’s a photo (courtesy of this website) of the same mechanism on a US locomotive of around the same vintage – the brake shoe is also clearly visible.

 Go to Wikipedia for the workings and components of a typical steam locomotive, and on the associated diagram, number 7 points out the sand dome (or sand box) and number 19 the sand pipe:

 
Look up “sand box” on Wikipedia and you will find the following:

A sandbox is a container on most locomotives and self propelled multiple units, or trams, (a type of train that runs on roads) that run on tramways and adhesion railways. The container holds sand, which can be dropped on to the rail to improve rail adhesion under very wet or steep conditions.

The sand may be delivered by gravity, by a steam-blast (steam locomotives) or by compressed air. Gravity sanding requires that the sand is dry so that it runs freely. Steam locomotives in the USA had a single sandbox, called a "sand dome" placed on top of the boiler where the rising heat helped to dry the sand. Even with this arrangement, sand pipes tended to clog, and by the 1880s, pneumatic sanding systems were being proposed. On diesel and electric locomotives and railcars, sandboxes were and are fitted close to the wheels so as to achieve the shortest possible length of delivery pipe. Depots may have a sand drier installed to warm and to dry the sand before it is used.

Our guide at the museum pointed out that that even this method of slowing down the train was hardly rapid – he told us that, from a speed of 120 km'/hr, it would take 100 kms to halt this train. We found this hard to believe – but he did point out that the distance from Milan to Bologna is 300kms.

 Now, this may seem like old technology, but it isn’t. The Wikipedia page on on the sand box includes the following image from a current UK train; note the reminder to “fill with dry sand only” – the assumption must be that the engineers responsible for maintaining this piece of kit have never built a sandcastle.

And, this is not the end of the story with respect to the value of arenaceous materials in the running of the railways. There is a standing joke here in the UK that originates from our illustrious rail network’s explanation of timetable disruptions by “the wrong kind of snow.” This is second in infamy to the  excuse of “leaves on the track.” It seems that autumnal shedding by the arboreal borders of much of this country’s rail system comes as something of a surprising inconvenience. But, yet again, sand comes to the rescue – through a material that I had never encountered before looking into the background for this post, a material that should be elevated to a prominent position in the arcane world of arenophilia: SANDITE!

 Please consult scot-rail.co.uk, “Scotland's online railway community,” to learn about methods that “are used to improve track conditions during the leaf fall season. This is done using a combination of water cannons and the application of sandite (a thick sand based paste that improves adhesion) to the rail surface.” Here's the delivery system - the tanks are, presumably, full of....sandite.

I never cease to be astonished…..

 

[Photos of the 691-022 from http://www.viaggivacanze.info/newsite/2011/02/milano-se-la-conosci%E2%80%A6-te-ne-innamori/ and http://commons.wikimedia.org/wiki/Category:FS_691; modern sand box image licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. Attribution: Roger W Haworth]

Suna

 
The calligraphy above translates from the Japanese as “sand sand sand sand.” Why my sudden interest in suna, as the Japanese word is transcribed? Simply because I very much appreciate that the first (and, so far, only) foreign translation of the book has now been published, and, being back in London, I now have the pleasure of holding a copy in my hands. And what a strange experience that is – something so intimately familiar, yet so inaccessibly alien:

 
It is a beautifully produced hardback publication (translated by Yumiko Hayashi and published by Tsukiji-Shokan), more compact than the US or UK editions. And it has what is now the third different cover graphic, and a separate wrap-around:

It, of course, starts from what is, for us, the back, a flip through the pages yielding only the occasional glimpse of familiarity – the illustrations:

And, having flipped for the first time, a sudden sense of alarm arose – where are the plates? A second flip revealed that they are indeed there, but all bound in at the very beginning (the back), before anything else.

So there it is, a fascinating symbol, an elegant example of Japanese script with its calligraphic variations. This instantly reminded me of one of the many personal discoveries made during the research for Sand, the strange, often surreal, yet compelling book by Kono Abe and film by Hiroshi Teshigahara, Suna no onna, “Woman of the Dunes.” Sometimes translated as “Woman in the Dunes,” the original title is, more accurately, simply “Sand Woman.”  

Here’s what I briefly wrote in Chapter 5:

Woman in the Dunes, the 1964 film by Hiroshi Teshigahara, won the Grand Jury Prize at Cannes and was nominated for two Oscars. Based on the novel by Kobo Abe, the setting is the sweeping wilderness of sand dunes along the Japanese coast at Tottori. An amateur insect collector finds himself abducted and consigned to cohabit with a woman whose crumbling house lies at the bottom of a deep depression in the dunes; she exists “only for the purpose of clearing away the sand.” The sand constantly threatens the house, an outpost on the edge of a village, “already corroded by the sand,” whose way of life is defined by fighting the dunes and selling the salt-tainted sand—illegally—to construction companies. In both the book and the film, sand is the enemy but also the central character. The meticulous cinematography and Abe’s writing beautifully document sand grains and their movement: liquid avalanches descending on the house, windblown grains, and the forms of shifting dunes. The book is a lesson in the behaviors of granular materials. And, inevitably, the sand is a powerful metaphor for time: “Monotonous weeks of sand and night had gone by.”

Looking at various original film posters and book covers, there it is, in yet further variations, the symbol that I have now become quite fascinated by:

So, my thanks to the Japanese publishers – and their readers – for their interest and my novel experience. And, if any readers of this blog could provide me with a translation of what, in particular, the wrap-around says, I would be most interested!

Wave base, moving sand - and the first underwater feature film on TtS

In addition to my hyper-sophisticated new camera, knowing that there would be snorkelling on our recent trip, I also treated myself to a very modestly priced little camera that is good to 3 meters underwater – and wow, am I glad that I did, it’s amazing. Having overcome the initial sense of horror at jumping into the sea with a camera, I managed to record, albeit amateurishly, in still images and on film, much of the spectacularly beautiful and fascinating world that even a simple snorkel allows you to witness.

Once the ungainly (and abrasive) process of donning flippers in the beach swash zone of the waves is complete, progress seaward reveals the zone of wave-activated sand before depths acceptable for the coral gardens are reached. The variety of types of coral is simply astonishing, never mind the fish, for which the hackneyed word “teeming” is the only appropriate one that comes to mind.

But, of course, the areno-nerd also found that barren sandy zone of some considerable interest. From where the waves break on the beach out to a water depth of around a couple meters, the action is too violent for the corals – but the action is played out by the sand. Ralph Bagnold, having finished all he could do with desert sand (lacking the necessary comprehensive long-term wind data), turned his attention to sand transport in water, and described how he spent many hours simply floating around in shallow waters observing the movement of sand; I understand his fascination. For, even on a calm day, with very modest waves, the sandy bottom is a stage for tempests of grains and what for all the world look like miniature aqueous sandstorms, and yours truly spent some time attempting to document the action.

The bedforms are diverse – large scale ripples and small-scale dunes, one of these looking exactly like a star dune in the desert but on a rather smaller scale:

The action is directed and produced by the waves. The corals stay safely below normal wave base, but here everything is in motion. The movement of water as a wave passes takes on the form of a series of circular orbital paths, their diameter decreasing exponentially with depth, as shown at 2 in this illustration (thanks to the Intro Geology Course at Fort Hays State University):

 

The scale of water movement is related non-linearly to the wavelength, and essentially that movement becomes trivial at depths greater than half the wavelength – the depth known as the wave base, below which virtually no sediment is moved and corals are happy. But something else goes on as a wave approaches the shallowing sea floor on its way to the beach – the water column becomes squashed, compressed by the lack of room to move, with the result that the orbits become elliptical and the wave crests sharper and higher (3 in the illustration above). This is, of course, particularly dramatic and catastrophic in the event that the water movement is that of a tsunami – but then that is also no ordinary wave. So, off the beach, above wave base, these elliptical orbits energetically pick up sand – and, as the wave passes, move it back and forth, incessantly, and, I found, compellingly. Shape-shifting again, the ripples and mini-dunes constantly destroyed and reformed.

Here are a couple of stills from the movie (I de-saturated them and modified the contrast, since underwater colour is difficult to reproduce accurately), and then – the movie.

 
 

This is not a storm, the waves are not exactly pounding (the photo below shows the beach – and yes, the colour is accurate - more of that in a later post); but just look at the scale of sand movement on a normal day, and imagine what this would look like during a hurricane.  

But I must end by returning to below wave base and include just a few of the denizens of these wondrous underwater landscapes.

 

Tugu Beach: black sands on the move - and sand ladies

 
A week shipboard, tossed about in a small cabin, simple and basic, always creaking, and with the ever-present and heady aroma of diesel fumes (I won’t go into any details on the bathroom), was worth every minute for the experience and the spectacular places visited. But, by the time we returned to Bali (before the earthquake), a little landlubber luxury was definitely in order. This we attained superbly with a two-night stay at the Tugu Hotel in Canggu, blissfully removed from the manic hustle and traffic of Kuta and Denpasar. This kind of quintessentially Indonesian hotel, with its superb rooms, excellent food, beautiful grounds, and ever-attentive and friendly staff, comes, of course at a price – but a price that would nevertheless secure you not very much by way of a New York or London hotel, and a price that was worth every rupiah. And, while this blog is explicitly non-commercial, I can only recommend the Tugu as a gloriously different place to stay. As a flavour of what I mean, here, taken from our room (using the amazing “hand-held twilight” noise reduction function of my new toy), is the setting for our dinner the first night, next to the lotus pond, listening to the sound of the surf:

 
Which, inevitably, brings me to the shore. The surf was up and the surfers were out, but my focus was, of course, on the details of the beach. Here, the sand is a chromatically dramatic mix of glistening black volcanic grains (with occasional apple-green glints of the mineral olivine), glittering quartz, shell fragments, and our ubiquitous friends, the foraminifera.  

This palette, when used by the constant brush of the waves, yields delightful beach patterns. But, better still, where a stream comes down to the beach, and the heavier black volcanic grains behave differently from their lighter-weight colleagues (the placer effect of granular segregation), then things become quite spectacular.

 
This stream had carved out a miniature valley, revealing the old layers of storm sands that constantly avalanched down into the flow, a small-scale animated exhibit of earth surface processes.

And then the stream flow went to to work transporting and sorting the sand, sculpting it into ripples and small dunes, each structure graphically defined by the dark and light grains. A dynamic, shape-shifting system – and, being the areno-nerd that I am, I spent some time simply watching the ripples move, forming and re-forming, swirling and migrating. And here’s the movie:

   

Once carried down to the shore, the sand is then entered in a new transportation game, and becomes the massive cargo of unceasing wave action.

This being Indonesia, Tugu Beach is not simply a place for surfers and basking tourists – it is a hive of entrepreneurial (and undoubtedly illegal) activity. Sand is a valuable commodity here, and there was an industrious group of women (who, traditionally, do all the hard work in Bali), digging up sand, filling bags, and then taking them away by carrying them on their heads:

Every day in Indonesia brings some new experiences, some unexpected surprises – Tugu Beach proved to be a place where all of these were pleasurable.

 

A flavour of things to come (but probably later rather than sooner)

I am now returned from what can only be described as an utterly memorable and spectacular trip. Although it began with some uncertainty when we found that our original transport/hotel, the Ombak Putih, was belching noxious black smoke after an engine overhaul, we transferred to the miraculously available Sea Safari VII:

Looking for all the world like a pirate ship – which, after all, the original Bugis phinisi vessels, on which she is based, often were (raiders of the Makassar Straits) - she proved a very comfortable (if basic) means of enjoying the glorious landscapes, seascapes, and peoples of Nusa Tenggara, with a delightful crew, good food, and more than sufficient supplies of cold beer. The only disappointment was that, unlike the Ombak Putih, her height did not allow the sails to be unfurled and actually put into action; however, stability is important, and, regardless, the experiences of the voyage far outweighed this piece of the equation. For example, here is our trusty transport moored in one of the bays of Komodo Island – where, I can assure you, there definitely be dragons, and remarkably unpleasant creatures they are.

 
There are countless tales to tell, and told many of them will be. Here, for example, are some characters that will feature in future editions of Sunday Sands:

 
However, over the next couple of weeks, the telling of tales may well be sporadic: I leave soon for a return to the UK and a trip to Milan where I will be giving an invited talk at the international conference of the American Association of Petroleum Geologists (you can, perhaps, make a guess as to my general topic – but it will, specifically, be an appeal for geologists to “interface” with the remarkable work going on in the world of the physics of granular materials, a potentially fruitful conversation that, surprisingly, does not seem to take place very often).

But as a result of this, and the inevitable domestic tasks after being away from my London home base for six months, posts may be irregular; I have an extensive photographic archive from the trip (to be precise, over 1000 pictures) and these will at least provide grist for the visual mill. I have always tried to routinely split infinitives but, more importantly, post something vaguely scientific (reporting on active research that I find fascinating), and I am acutely conscious of my recent dereliction with respect to this; all I can say is that time eludes me, but that I shall endeavour to return to fulfilling this aspiration.

For now, psammophiles: the variety of flora and fauna that find sand a pleasing habitat never ceases to amaze me – I had not properly appreciated that mangroves fall into this category: