Through The Sandglass

An Antipodean adventure and an extended hiatus

 
From this Friday, I will be essentially – and, I must admit, largely blissfully – out of touch with the world. I am off on an epic four-wheel-drive tour of a large chunk of the Australian outback, starting and ending in Alice Springs, and traversing four deserts, the Tanami, the Great Sandy, the Little Sandy, and the Gibson. Here’s a general map of the route:

As a result, there will be a hiatus in terms of new posts for a while, but I suspect that I might have a few topics in mind by the time I return. If you spot any entertaining arenaceous items in the news while I’m away, please let me know!

 

[For those interested, more details can be found here; the majority of time on the trip will be navigating the Canning Stock Route through a region resonant with exploration history and indigenous culture – many of the images at the head of this post are taken from an Australian Geographic article, and there is a wonderful resource on The Canning Stock Route Project, a recent art-based initiative designed to “explore the cultural diversity of Aboriginal communities and their interconnections with each other and their Country and their part in a greater Australian story.”]

Icons old and deep

 
Thanks to Walter for bringing to my attention this particularly resonant and compelling image from the recent coverage of the investigation of a dramatic shipwreck in the Gulf of Mexico.

Here’s part of the original report from NOAA:

NOAA, BOEM: Historic, 19th century shipwreck discovered in northern Gulf of Mexico

May 16, 2012

  While most of the ship's wood has long since disintegrated, copper that sheathed the hull beneath the waterline as a protection against marine-boring organisms remains, leaving a copper shell retaining the form of the ship. The copper has turned green due to oxidation and chemical processes over more than a century on the seafloor. Oxidized copper sheathing and possible draft marks are visible on the bow of the ship.(Credit: NOAA Okeanos Explorer Program.)

During a recent Gulf of Mexico expedition, NOAA, BOEM and partners discovered an historic wooden-hulled vessel which is believed to have sunk as long as 200 years ago. Scientists on board the NOAA Ship Okeanos Explorer used underwater robots with lights and high definition cameras to view remnants of the ship laden with anchors, navigational instruments, glass bottles, ceramic plates, cannons, and boxes of muskets.

Equipped with telepresence technology, Okeanos Explorer reached audiences around the world who participated in the expedition through live streaming Internet video. As members of the public ashore watched live video from the ocean bottom, they became “citizen explorers,” sharing in the discovery with maritime archaeologists, scientists and resource managers from a variety of federal, academic, and private organizations.

The NOAA-funded 56-day expedition that ended April 29 was exploring poorly known regions of the Gulf, mapping and imaging unknown or little-known features and habitats, developing and testing a method to measure the rate that gas rises from naturally-occurring seeps on the seafloor, and investigating potential shipwreck sites.

The shipwreck site was originally identified as an unknown sonar contact during a 2011 oil and gas survey for Shell Oil Company. The Department of Interior’s Bureau of Ocean Energy Management (BOEM) requested this and other potential shipwreck sites be investigated during NOAA’s Gulf of Mexico expedition. Surveys and archaeological assessments are required by BOEM to aid in its decision-making prior to issuing permits for bottom-disturbing activities related to oil and gas exploration and development.

“Artifacts in and around the wreck and the hull’s copper sheathing may date the vessel to the early to mid-19th century,” said Jack Irion, Ph.D., a maritime archaeologist with BOEM. “Some of the more datable objects include what appears to be a type of ceramic plate that was popular between 1800 and 1830, and a wide variety of glass bottles. A rare ship’s stove on the site is one of only a handful of surviving examples in the world and the second one found on a shipwreck in the Gulf of Mexico.”

Significant historical events occurring in the regions around the Gulf of Mexico during this time include the War of 1812, events leading to the Texas Revolution, and the Mexican-American War, he said.

“Shipwrecks help to fill in some of the unwritten pages of history,” said Frank Cantelas, a maritime archaeologist with NOAA’s Office of Ocean Exploration and Research. “We explored four shipwrecks during this expedition and I believe this wreck was by far the most interesting and historic. The site is nearly 200 miles off the Gulf coast in over 4,000 feet of water in a relatively unexplored area.”

The news has been reported widely, these extracts being from CBS News and the Associated Press:

"When we saw it we were all just astonished because it was beautifully preserved, and by that I mean for a 200-year-old shipwreck," said Jack Irion, maritime archaeologist with the Department of the Interior's Bureau of Ocean Energy Management in New Orleans… Among the wreckage were "a rather astonishing number of bottles," particularly square gin bottles known as case bottles, as well as wine bottles, Irion said. There were many ceramic cups, plates and bowls that didn't appear to be cargo. Some were green shell-edged pearl ware, a British import popular in the United States between 1800 and 1830. The ship's kitchen stove was found intact. "Very few shipwrecks have been found that still have the stove intact," Irion said. "You can very clearly see the features of the stove. It's in rather good shape." Also discovered were an anchor, cannons and muskets. Irion said researchers have not yet determined whether it was a merchant, military or pirate ship… The wreckage can also give insight to the lives of the crew, where they had been, where they were going and their role in the economy and world history. "It's as if we get a glimpse into what their lives were like, like a time capsule," Irion said.

All kinds of fascinating stuff, but I can’t understand why no mention of the sandglasses lying in the sand…

Black sands, black crystals, and a green queen

 
Pelabuhan Ratu, a sweeping beach on the south coast of Java pounded continuously by the breakers of the Indian Ocean. A popular destination, but one that I have not visited – today’s feature comes courtesy of, and with thanks to, Carol Banks, the latest recruit to my growing army of sand-snatchers.

Pelabuhan Ratu means “Queen’s harbour,” and the place comes with myths and legends galore – but more of that later: for now, the sand. The most popular and developed part of the long beach is a typical tropical white, but great stretches are also gloomily black and less attractive – except to an arenophile, for this is a lovely sand.

I chose the Google Earth image above to show the less-developed section, the river clearly bringing its cargo of black sands down to the coast. When the sand is wet, it is truly a dark charcoal-grey colour, but dry it out and it takes on a speckled brown and grey character – not particularly attractive at first glance. But look closely, and you will see transparent quartz grains, glittering like diamonds amongst the dull fragments of dark volcanic rock. Then there are the grains of the local limestones, together with a few shell fragments, shattered by the surf.

Looking more closely, those grains of transparent volcanic quartz really are beautiful:

 
A number of them, dramatically the one at the upper right, show conchoidal fractures. These are where a material breaks along curved surfaces, often complex and rippled, very much the form of a mussel shell, hence the name (from the Greek for mussel or cockle). This behaviour is typical of amorphous materials such as glass and its natural volcanic version, obsidian – it’s this kind of fracturing that is exploited in the making of obsidian and flint tools. Strictly amorphous materials such as glass have no internal structure to guide fractures; this is not true of quartz, but its mineral structure, and the strength of the bonds between the silicon and oxygen atoms, make it behave very much as if it were amorphous.

The apple-green jewels amongst the grains are the mineral olivine, a common constituent of the kinds of volcanic materials of which Java is constructed. Shine the microscope light through the sand, and the glowing glory of these grains is revealed:

But, in the first group of microscope photos above, there are also very distinctive tiny black grains, clustering together, looking vaguely metallic, and often of a very regular, geometric, shape. What are they? Well, the answer is easily discovered by passing a magnet over the surface of the sand – these little grains defy gravity and hurl themselves upwards on to the magnet’s surface, reasonable behaviour for magnetite.

Magnetite is an iron oxide, chemical formula Fe₃O₄, and is another common constituent of the local volcanic rocks; it’s the most magnetic of all minerals, and is the key to the lodestone, used for early compasses. Left free to fulfil its ambitions, magnetite can form large clusters of glorious crystals such as this specimen, up to ten centimetres across, from one of the mines in St. Lawrence County New York, and in the collection of the New York State Academy of Mineralogy. Unfortunately, since it is a valuable source of iron, magnetite has a social dark side: because it is heavy, the waves of the beach concentrate the grains into placer deposits, and, along the south coast of Java these have been the source of sometimes violent conflicts between developers and local farming communities. But back to the bright side of magnetite, so to speak.

Because these grains do form placer deposits, a little amateur panning in the kitchen separated them out from the lighter grains (I could, of course, have used my magnet, but that wouldn’t have been so much fun). Here are some family portraits:

The amazing thing is that so many of these grains are hardly worn at all, and their original crystal shape is preserved. Look at the one that seems like two pyramids stuck together – that’s the original octohedral form of the mineral, a single, almost perfect, crystal of magnetite. Raw diamonds are often octohedral, but these grains are just humble iron oxide – beautiful nevertheless, don’t you think?

So, what about the queen whose harbour, or bay, is Pelabuhan Ratu? Well, this stretch of the Java coast is the haunt of Nyai Roro Kidul, the mythical Queen of the Indian Ocean in these parts, and a shape-shifting spirit of Javanese and Sundanese folklore. She is, of course, beautiful, but she is powerful, able to take your soul on a whim. Various versions of the legend describe how a beautiful princess was struck with black magic by a jealous rival in the palace and developed a horrible skin disease. She fled to the ocean and plunged into the waves, where she was cured and crowned queen by the marine spirits and demons. Her sacred colour is green, and there is a local belief that wearing green will anger Nyai Roro Kidul – so, arenophiles, should you visit Pelabuhan Ratu, please choose your outfit with this in mind.

A sad story of desert preservation

 
A story that appeared all over the news recently caught my eye for a number of reasons - here’s an example of the headlines: “Frozen in the sands of time: Eerie Second World War RAF fighter plane discovered in the Sahara... 70 years after it crashed in the desert.”

The Western Desert of Egypt and Libya is strewn with well preserved wreckage from WW II, but this is an extraordinary example. This is the BBC description:

A World War II RAF fighter, which crash-landed in a remote part of the Egyptian desert in 1942, has been discovered almost intact. There was no trace of the pilot, Flt Sgt Dennis Copping, but the British embassy says it is planning to mount a search for his remains.

The RAF Museum in Hendon, north London, says it is hoping to recover the plane as soon as possible.There are fears souvenir hunters will start stripping it.

The 24-year-old pilot, the son of a dentist from Southend in Essex, went missing over the Western Desert in June 1942, flying an American-made P40 Kittyhawk single-engine fighter. Two-and-a-half months ago an aircraft believed to be his was discovered near a remote place called Wadi al-Jadid by a Polish oil worker, Jakub Perka. His photographs show the plane is in remarkably good condition, though the engine and propeller have separated from the fuselage. The original paintwork and RAF insignia are said to be clearly visible, almost perfectly preserved in the dry desert air.

But of the pilot there is no sign. He appears to have executed a near-perfect emergency landing, perhaps after becoming lost and running out of fuel, and to have survived the crash. He rigged a parachute as an awning and removed the aircraft's radio and batteries but then apparently walked off into the desert in search of help. Almost 100 miles from the nearest settlement, he stood virtually no chance.

David Keen, an aviation historian at the RAF Museum, says the pilot broke the first rule of survival in the desert, which is to stay with your plane or vehicle. But the very same conditions which made the pilot's prospects so bleak have helped preserve the plane. Mr Keen says of the many thousands of aircraft which were shot down or crashed during the Second World War, very few survive in anything like this condition.

He said: "Nearly all the crashes in the Second World War, and there were tens of thousands of them, resulted on impact with the aircraft breaking up, so the only bits that are recovered are fragments, often scattered over a wide area. "What makes this particular aircraft so special is that it looks complete, and it survived on the surface of the desert all these years. It's like a timewarp."

The RAF Museum has a P40 Kittyhawk on display, but it has been put together from parts of many different aircraft.

Recovering Flt Sgt Copping's plane will not be easy. It is in a part of the desert which is not only remote but also dangerous, because it is close to a smuggling route between Libya and Egypt. The defence attache at the British Embassy in Cairo, Paul Collins, says he is hoping to travel to the area in the near future, but is waiting for permission from the Egyptian army.

He told the BBC: "I have to go down there. This is a serviceman who was killed, albeit 70 years ago. We have a responsibility to go and find out whether it's his plane, though not necessarily to work out what happened. He went missing in action. We can only assume he got out and walked somewhere, so we have to do a search of the area for any remains, although it could be a wide area. But we have to go soon as all the souvenir hunters will be down there." 

He said the British authorities are trying to find out whether Flt Sgt Copping has any surviving close relatives, because if his remains are found a decision will need to be made about what to do with them.

A compelling story. And, of course, being a geologist and having spent some time in the Western Desert, I was curious – where, exactly, was the plane found? The location mentioned, Wadi al-Jadid, is a very large area south and west of the village of Mut, part of the sprawling oasis of Dakhla – through which I had passed, travelling to the southwest on my way to the Gilf Kebir several years ago. Geologists have a strange tendency to look at the rocks in a photo or in a movie (and, unnervingly for passengers, out of the car window while driving), and an examination of the photos above reveals a couple of things. First, all the gumph in the press reports about “buried in the sands of time” is exactly that – this is an area of sand-blasted limestone outcrops across which the blasting grains would bounce, swirl, and keep going: no dunes deep enough to have buried the plane could accumulate there. Second, the reports variously describe the location as being one hundred or “more than 200” miles from the nearest town, which is, perhaps, Mut. Vast areas to the south and west of Mut are covered by dunes sweeping across seemingly endless gravel plains – few outcrops,none of them limestone. Only after around 150 miles did we enter the distinctive blasted limestone landscapes. I would suggest that this image from my trip is evocative of the general environment shown in the photos of the plane:

I have no intention of providing a guide to bounty-hunters – the area shown on the Google Earth images below is still huge (and, anyway, I may be wrong - I am, see comment discussion below after this was posted):

And there is other scattered WWII wreckage strewn through this part of the desert:

The desert preserves, dramatically and effectively, with or without sand. From elsewhere on that trip are some further examples (the unopened can of sliced bacon, and the battery are from the 1930s):

Incidentally, the comment in the BBC piece that the area is “also dangerous, because it is close to a smuggling route between Libya and Egypt” I believe is somewhat misleading. Those photos come from the desert west of the Gilf Kebir and it is there, along the Libyan border, that certainly the main people smuggling routes run – I know (and wish that I didn’t), because we saw some of the trucks in the distance.

The CNN report describes how “The young pilot, according to [British military historian] Saunders apparently became disoriented during the flight and headed in the wrong direction. Another RAF pilot flying nearby ‘tried all sorts of things’ to get his attention, but Copping ‘bizarrely’ ignored a series of warnings.” So where should the pilot have been trying to get to? The Imperial War Museum website proves to be yet another wonderful internet resource. Here are two images from their online archives of the North African Campaign:

Left, “A Curtiss Kittyhawk Mark I of No. 112 Squadron RAF taxies through the sand at a landing ground in the Western Desert. A mechanic sitting on the wing is guiding the pilot, whose forward view is obscured by the aircraft's nose.” Right, “Trolleys loaded with 250-lb GP bombs are drawn up in front of a line of Curtiss Kittyhawk Mark IIIs of No. 260 Squadron RAF at Marble Arch landing ground, Libya, prior to a bombing sortie.” (Reproduced courtesy of the IWM Non-Commercial Licence).

 

These landing grounds were scattered across the Western Desert, but, appropriately, close to the Mediterranean coast; the Google Earth image above shows one of the British-American joint bases, RAF Gambut, from which the Kittyhawks flew. The pilot of this one was certainly, tragically, a long way from home.

 

 

 

 

Reposing differently on Mars

Sand, Mars, and a challenge to conventional wisdom. What better ingredients for a post could I wish for?

The two images above show sedimentary fan deposits, the great  - yes, fan-shaped – aprons of detritus that accumulate at the foot of a gully, driven by gravity, often, on earth at least, assisted by periodic torrents of water. Water is an interesting factor: on Earth these things are often called “alluvial fans” because the occasional flood clearly plays a role.

These images are an opportunity for a quiz, since one is from Earth and the other is from Mars – which is which? Sorry, but I’ll maintain the suspense for a while. Are the fans on Mars alluvial – is water involved? The debate about the role of water in Martian surface processes continues, and it’s fascinating and the evidence for,against, ambiguous, is diverse. One of the lines of reasoning involves the slopes of fan deposits – they can be characterised by lower angles than expected and this is cited as a result of the lubricating effect of water. But this makes one critical assumption: that the slope of a deposit of granular materials (the angle of repose) is not affected by the low gravity of Mars – the angle of repose is independent of gravity. But is this assumption correct? Oddly enough, this question had not been seriously addressed until Maarten Kleinhans of Utrecht University together with Sebastiaan de Vet of the Institute for Biodiversity and Ecosystem Dynamics (IBED) at the UvA and colleagues from Delft University of Technology decided to do so. How? Well, as the University press release describes, they took a plane:

The research team used a parabolic flight campaign to mimic Mars’s lower gravity and test the effect on angles of repose of different materials. As the plane followed its roller coaster style path, slowly rotating cylinders containing different materials experienced one tenth of Earth's gravity, Martian gravity and the Earth's normal pull.

And here, from their paper in the Journal of Geophysical Research, is the gravity-reducing plane.

 
But, before we look at what they found, let’s back up for a minute and remind ourselves about angle of repose. In its simplest sense it’s the slope that sand, or any granular material, naturally settles at after it has been poured. It varies substantially with the nature of the material – grain size and shape and so on. The paper included this helpful illustration of “A pile of rounded gravel at the angle of repose, built by Gijsbert F. Kleinhans.”

Because it’s important in many contexts, I have written several posts on the angle of repose, for example in kitchen physics, and “From Bogart to Bugs,” And it’s one of many principles of physics that can be observed simply by watching the flow of sand in this blog’s icon, the sandglass. But the sandglass, simple though it may appear, illustrates the complexity of many things, among them the angle of repose. For there is not one simple angle of repose for a given material – there is a static one and a dynamic one. Essentially, the static angle of repose is demonstrated when a pile of grains is at rest, but, once they start avalanching down a slope, the constant angle of the avalanche is different, and that’s the dynamic angle of repose, always lower than the static.

There are different ways of studying all this (should you be inclined – and many people are), but a classic is the rotating cylinder. This is basically like watching clothes in the drier – a transparent cylinder is partially filled with granular material and rotated – the sand, or whatever stuff you chose, cascades down-slope constantly at it’s dynamic angle of repose. When it comes to rest, it does so at its static angle. This is exactly the equipment that the Dutch researchers took up with them in their gravity-reducing plane: nine cylinders half-filled with sand, gravel, glass beads, some in air, some in water, their behaviours captured by HD video cameras:

All kinds of clever corrections for the noise and accelerations of the aircraft itself were applied. Each stomach-churning parabola allowed for around 20 seconds of experiment at gravities of down to one tenth the normal earthly value – the gravity on Mars is just over a third of Earth’s.

As the authors write in their paper, “Our main result is surprising.” They found that, with decreasing gravity, the static angle typically increases by around 5 degrees, whereas the dynamic angle decreases by about 10 degrees. And this is true of all the materials and regardless of whether they were in air or water – the angle of repose is not independent of gravity. The difference between the two angles is critical to the natural behaviours of granular materials, and in these experiments it increased by roughly an order of magnitude. Why is this important? If the static angle is higher, then a slope can build more steeply, but, once stability is lost, then avalanches cascade down the slope at the dynamic angle – if this is low, then the avalanches keep going and involve more material.

So, bigger avalanches, lower slopes on Mars are possible without the lubricating effect of water. And, as the authors point out, this gravity dependency of the angle of repose has implications for a wide variety of phenomena on Mars and elsewhere.

Ah yes, the answer to the quiz: it was great fun juxtaposing these images (well, to me at least) because of their remarkable similarities. The image on the left is of gullies and fans in a severely eroded 100 kilometer impact crater in the southern polar region of Mars (courtesy NASA/JPL/University of Arizona). On the right is a Digital Elevation Model (DEM) image of gullies and fans on Svalbard (a.k.a. Spitsbergen) from the Europlanet HRSC-AX flight campaign. The laws of physics are compellingly universal.

 

[Many thanks to Brian Romans of Clastic Detritus for catching this paper for me. Paper citation: Kleinhans, M. G., H. Markies, S. J. de Vet, A. C. in 't Veld, and F. N. Postema (2011), Static and dynamic angles of repose in loose granular materials under reduced gravity, J. Geophys. Res., 116, E11004, doi:10.1029/2011JE003865.]