Through The Sandglass

A sacred mountain

I have taken countless photographs of Mont Canigou, since this view is from my place in France and the mountain's mood and appearance are ever-changing, ever compelling. This particular mood is from just a few minutes ago. Canigou dominates this part of Roussillon, barely in France and certainly in greater Catalonia (village name signs are in both languages and the culture is deeply Catalan). It's no wonder that Canigou is a sacred mountain for the Catalans - it's inspiring to anyone. It's not the highest peak in the Pyrenees, but its isolated grandeur earns it pride of place. Oh, and the geology's great, too....

Holiday greetings

Original image of a granular gas experimental model: thanks to Matthias Schröter at the Max Planck Institute for Dynamics and Self-Organisation in Göttingen for his guided tour of the facility.

 

Jindal berms, Jindal berms

 
We are approaching that time of the year when reflections on events and lessons learned from the previous twelve months are in vogue – and, depressingly more often than not, the events are tragic and no lessons were learned. It has not been the habit of Through the Sandglass to indulge in such reflections, but this year the timing of a report on a topic that your humble correspondent devoted much attention to is too compelling to ignore. I refer, of course, to the draft report of the Presidential Commission investigating the Gulf of Mexico oil disaster. As reported in the New York Times, “A chain of sand berms built by the State of Louisiana to block and capture oil from BP’s runaway well in the Gulf of Mexico stopped a “minuscule” amount of oil and was largely a waste of money.”

A waste of a very large amount of money. The political posturing and dissembling (there are other words that I’m tempted to use, but I won’t) beggars belief – but it continues, as does the mindless bulldozing (the image above is from last week). Anyone who has read the numerous dispatches in this blog and, more importantly, the links to reports and views of people who actually know what they are talking about, will have no problem discerning the absurdity of some of the statements of Louisiana officials quoted below; the idea that this has now transmuted into a barrier island restoration project would be laughable if it were not so dangerous. This whole project has been, for want of a better word, a scam. 

I will take the liberty of quoting from the New York Times writer, John Collins Rudolf, who, in his report of the 16th December, wrote:

A chain of sand berms built by the State of Louisiana to block and capture oil from BP’s runaway well in the Gulf of Mexico stopped a “minuscule” amount of oil and was largely a waste of money, the staff of the presidential commission investigating the spill said in a report issued on Thursday.

The report, a draft, found that a decision by Thad W. Allen, the retired Coast Guard admiral who led the spill response, to approve construction of the berms was made under “intense political pressure” from federal, state and local politicians and against the advice of an expert panel advising on the spill response.

“The decision to green-light the underwhelmingly effective, overwhelmingly expensive Louisiana berms project was flawed,” the commission staff wrote.

The berms were first proposed by a Dutch engineering firm and became a top priority for Gov. Bobby Jindal of Louisiana, who exhorted President Obama and federal agencies to authorize the project. The state drew up plans for 101 miles of berms and requested a permit from the Army Corps of Engineers.

The panel of experts advising the response effort determined that the structures could not be built quickly enough, and federal responders initially leaned toward rejecting the plan, the report found. But after aggressive lobbying by state and local officials and intervention by the White House, Admiral Allen approved the construction of six segments of berms in late May. BP then agreed to pay $360 million for construction of approximately 40 miles of berms.

In a statement, Admiral Allen said that responsibility for authorizing the barriers rested solely with him. “The ultimate approval of this proposal was my decision,” he wrote.

By October, about 10 miles of berms had been built several miles from the gulf coastline at a cost of $220 million, with construction paid for entirely by BP. Louisiana officials estimate that the berms stopped 1,000 barrels of oil from the spill.

By contrast, more than 800,000 barrels were captured at the wellhead, and roughly 270,000 barrels were burned off by Coast Guard vessels. Skimming operations recovered at least 34 million gallons of oil-water mixture.

“$220 million for a spill response measure that trapped not much more than 1,000 barrels of oil is not a compelling cost-benefit tradeoff,” the commission staff wrote.

In a letter to the commission on Thursday, Garret Graves, director of the Louisiana Office of Coastal Activities and leader of the sand berm project, insisted that the berms had achieved their purpose. “A number of photographs, surveys and interviews suggest that the berms were successful at stopping oil,” Mr. Graves wrote.

Governor Jindal criticized the report’s conclusions as “partisan revisionist history,” and drew attention to the coastal restoration benefits of the sand berms. “We are thrilled that this has become the state’s largest barrier island restoration project in history,” Mr. Jindal said.

Louisiana officials continued to build the berms months after BP’s well was capped, when much of the rest of the oil spill response had shifted from stopping oil to long-term restoration.

In October, under criticism from federal officials and environmental groups, the state declared it would largely halt construction of new berms and shift about $100 million of the remaining project money into a long-term coastal restoration effort.

The report acknowledged that the berms could potentially have a positive impact on Louisiana’s degraded coastline, but said that issue should be considered separately from their value as an oil spill response.

The Washington Post carried an article on the report in which it stated that:

The report cites an e-mail from Thad W. Allen, the retired Coast Guard admiral who was the federal government's point man on the spill, in which he asked, "What are the chances we could pick a couple of no-brainer projects and call them prototypes to give us some trade space on the larger issue and give that to [Louisiana Gov. Bobby] Jindal this weekend?"

I am, like, I suspect, many people, lost for further words. I will simply end with a few seasonal lines penned by the poet-in-residence at Through the Sandglass, Richard Bready:

Jindal berms, Jindal berms, 

Swindle all the way,

Hardly stopped a drop of oil but got a lot of pay.

Sunday sand: green grains of Groningen (and a lot of gas)

Having celebrated the sand enthusiasts of the Netherlands in my previous post, it’s an appropriate time for a Dutch sand (again, thanks to Carla) – one that displays, with subtle understatement, some seasonal colours (although, given the current weather conditions in Northern Europe, this should perhaps be white). Near the city of Groningen, in Northern Holland, is a lake, the Sellingerbeetse. It’s not a natural lake, but rather one that formed from waters flooding a very large hole in the ground, a hole created by sand mining.

 
These sands were deposited during the ice ages, but are probably marine, glacial debris being reworked and winnowed in shallow seas of an interglacial period, and their subtle colours reflect this. The beautiful blue-green hue results from grains being coated with a thin veneer of the mineral glauconite, so named from the Greek glaucos, meaning, oddly enough, blue-green. Glauconite is an iron-potassium member of the phyllosilicate group of minerals, the micas, whose crystalline form appears as thin sheets  - if you insist, glauconite’s empirical formula is K_0.6Na_0.05Fe³⁺_1.3Mg_0.4Fe²⁺_0.2Al_0.3Si_3.8O₁₀(OH)₂

Glauconite is a common mineral in sedimentary rocks, particularly sands and sandstones, and was first recognised as being widespread during the nineteenth century research voyage of HMS Challenger. It forms by the chemical alteration of unstable mineral grains, for example, the mica, biotite, contained in sands gently moving around and accumulating in shallow marine conditions. Many of the green sands of the world result from their glauconite content, exceptions being where the grains themselves are green minerals, such as the olivine sands of Hawaii. The mineral has been used as a pigment and, because of its potassium content, a fertiliser.

But while we’re talking about Groningen, it should be mentioned that, deep below the fields of crops, is another kind of field, and one that owes its fame to sand. Europe’s largest gas field, and the tenth biggest in the world, lies below Groningen and takes its name from the city and the province. Discovered in 1959, the Groningen gas field covers an area of 900 square kilometres and contained a staggering 99 trillion cubic feet, 2,800 billion cubic metres of recoverable natural gas, a large portion of which still remains. Its discovery revealed the foolishness of the conventional wisdom of the time that there was no oil or gas in Northern Europe or the North Sea; enough said about conventional wisdom. The rocks that contain the gas, the reservoir, are sandstones, 250 million years old, formed during the dire conditions of the Permian period when desert environments dominated much of the planet and the greatest extinction of life was imminent (see a couple of posts from last year). Blowing dunes bordered densely saline seas and flash floods delivered their cargoes of sand to the salt flats and the shorelines. Great thicknesses of sand and salt accumulated and were buried, but the spaces between the sand grains ultimately provided these rocks with sufficient porosity to store the huge volumes of gas that eventually migrated into them. These rocks, known in Northern Europe as the Zechstein formation, form the reservoirs for much of the region’s gas reserves, and were responsible for kick-starting the successful search for indigenous energy sources, along with the technology and infrastructure to effectively manage extraction and use. Furthermore, the scale and value of the Groningen gas field was eventually recognised as worthy of more than simply mass production: it is now managed as a “swing producer,” its remaining reserves conserved except during times of demand that exceeds the capacity of smaller fields – and, judging by the weather conditions at the moment, Groningen may well be fulfilling exactly this function as I write. A detailed description and history of the Groningen gas field can be found here.

Sands modern and ancient, green and red (the dire conditions continued - the Zechstein is overlain by the Triassic sandstones that I wrote about earlier this month); we should leave the arid world of the Permo-Triassic return to the relatively benign surface of Groningen with another image of Carla’s glauconitic Sellingerbeetse grains.

A sand enthusiast - and a creative idea

I’m not at all clear why it should be so, but it seems to be a fact that continental Europe is home to far more people who enjoy the fascination, beauty, and diversity of the sands of the world than is, even in proportion to population, the UK. I’ve written a little about sand enthusiasts, arenophiles, before, and those whom I have encountered, even virtually, are Italian, French, German, and, in particular, Dutch. My own very modest collection has been very much enhanced and augmented by the generosity of two Dutch collectors, one of whom I shall focus on today. Carla has not only sent me a wide-ranging selection of samples, but also pointed to beaches of interest along the French Atlantic coast prior to my grand expedition last year – for example, the spectacular garnet placer sands of Bretignolles. She and I continue to share information and ideas by email, and not long ago she wrote that she and her husband were off to Utrecht for a special “sand day” put on by a couple of the local geological societies. I was impressed to learn that there was sufficient general interest to organize this kind of thing – has there ever been such an event in the UK? But I was further impressed to see what Carla and her husband had prepared for the exhibition: six display boxes, each on a different sand theme –  and each with descriptions of origins, uses, minerals, and organisms of the sands displayed. These are not only beautifully and thoughtfully made, but they are highly informative, educational and attention-grabbing – three examples are shown at the head of this post (click on the image to enlarge). Of course, the text is in Dutch, but visual quality and effect is visible to anyone. Here's the detail of part of the display on mineral sands:

I asked Carla if she would describe the ideas behind these boxes and the way they are put together. Here’s what she wrote (and, by the way, she confesses concern about her English – I’m sure that any reader will agree that Carla’s command of a non-native language puts the rest of us to shame… And I had to check on passe-partout: it’s what is otherwise referred to as card mat, or mountboard, used in framing)

My exhibition boxes (size 35 x 45 x 5 cm)

As my sand collection has grown to almost 13.000 samples I felt the urge to finally think up something more useful to do with the sand samples than what I did before. The choice of sand samples is now quite extensive. So….why should I not bring more people into contact with this material in all its aspects by showing them a varied choice of samples together with some text and pictures, so they will never again say: “Isn’t sand just sand?”

By means of several self-made exhibition boxes I can show people many different types of sand samples: (heavy) mineral samples, biogenic samples, desert samples, river samples, etc.

More boxes will follow next year, to start with one about the size and appearance of sand grains. Actually this will be the most important one of them all, but..well.. that’s how I am..

The self-made boxes have a painted wooden frame covered by a glass plate, which can be taken out by removing one of the top laths at the short side, which has been screwed on to the box for this purpose.

The lay-out inside contains a passe-partout (the kind to frame photographs), in a colour matching the samples (desert sands!). Several quadrangles have been cut out for text and pictures. Some pictures are my macro photographs of sand. Because I do not always carry a microscope this is a good alternative for people to get an idea of the kind of sand.

I fixed the plastic boxes with sand (micro mount boxes or a larger kind, often used for minerals, micro fossils, tiny crystals, beads, seeds) on to the passe-partout with pieces of double-sided tape.

The paper for the text is a special kind of paper which will not discolour. At least…..that’s what I have been told.

As the wooden boxes are not really very large I noticed its limits too well, but alas, my house is not a palace and one has to keep count with the available storage capacity. So size is important and, more or less to my regret, the additional information had to be rather brief. As a Dutch person I decided to use my own language as the purpose of the boxes is mainly to show them on occasional meetings or exhibitions here in the Netherlands.

Designing the boxes was actually great fun, every case got its own appearance. I hope people will start to think differently about sand after a close look at the contents.

Carla.

I think that this is fantastic, and can only salute her enthusiasm and creativity. She would also seem to be extremely well-organized – here are some photos of a minute part of her collection (and note how dramatically the sands of Australia, on the left, capture its geology, and contrast it with the composition of New Zealand, on the right).

So many thanks, Carla – and keep up the good work! Any closet emulators hiding in the UK, or do I have to go to the Netherlands?

I’ll finish with one of Carla’s stunning photos – the foraminifera Ammonia beccarii from Corsica, relatives of the critters that have appeared in some of my Sunday Sand series.

Sunday sand: where's Walter?

Not long ago, my old friend (in every sense), Walter, set down in front of me a wonderful and equally venerable Dutch tobacco tin. This he had retrieved from a far-flung and dusty corner of his remarkable forge in the rolling hills of Pennsylvania – I can vouch for the fact that, given the complexity and number of such dusty corners, his locating it attests to the fine state of his memory.

He opened the can with care and relish and revealed the contents: a mystery sand from an Oregon beach. It seems that the fine state of his memory only extended so far: he could not recall where he was when he collected it (it was, after all, the 1960s). The beach was purple-grey-green, iridescent in the sunlight, and the sand an interesting pot pourri of local ingredients. It’s so poorly sorted that the larger grains don’t qualify as sand at all, being more towards the gravel family (the left image is simply a desk-top photo). This, together with the angularity of many of the grains, suggested to me that this is a river sand, but Walter insists that he was on a beach – somewhere in Oregon.

 
Now there are parts of the Oregon coast that are renowned for black and grey sand beaches – indeed, the inappropriately named Gold Beach is one (shown here). These beaches are along the southern coast of the state, and the ingredients derive from the typically complex geology of the interior, particularly that of the the Klamath Mountains. The geology records the same kind of tectonic mayhem that is found all down the west coast of North America, and similar to that of the San Francisco area, one of whose sands I’ve described before. But up in Oregon, there’s a further complication, and added ingredient – the volcanoes of the Cascade Range. Another analogy with the geology further south is the mining history of Oregon: placer sands yielding, amongst other treasures, gold and platinum – hence, perhaps, the name of Gold Beach. The mining activity took place along the major rivers draining the mineral-rich terrains of the interior – the Coos, the Coquille, the Rogue. These rivers brought their cargoes of sand down to the coast where waves and storms continued the winnowing and sorting, and concentrated placer deposits of minerals have also been (and in places still are) mined along the beaches and old coastal terraces. The geological map of southwest Oregon (thanks to Andrew Alden and his online collection) shows the diversity of ingredients delivered to the coast: in red and pinks, the young volcanics of the Cascades, in yellows and greens the sedimentary and volcanic rocks of old collisional terrains (together with patches of granites in red), in purple fragments of oceanic crust and mantle caught up in the turmoil, and in brown around Coos Bay, the detritus of all this chaos.  

So it seems to me that Walter’s sand probably comes from that stretch of coast south of Coos Bay, where the beaches are dark and the rivers supply endless loads of poorly sorted sediments for the coastal processes to play with. Any other ideas in this game of “Where’s Walter”?

[For those interested in the black sands of Oregon and details of the state's placer mining history, here are some further links: the Oregon History Project, Netarts Bay, a 1903 article on Rogue River platinum, beach mining history in California and Oregon, and a couple of articles from The Ore Bin, a publication of Oregon's Department of Geology and Mineral Industries - one here (see page45) and the other here (see page 21).]

Snot's troglodytes and rifting continents

 
I was born in Nottingham – some time around the late Pliocene: there’s a plaque somewhere, I’m sure. Nottingham is an old city, founded in Saxon times, when it was known as Snotengaham, the place where Snot’s people lived; it was strategically sited on sandstone bluffs overlooking the river Trent and the Norman invaders would later build their castle there. The city is, of course, best known for the legend  of Robin Hood and his merry men (and, presumably, women), and draws many visitors for that reason. But the castle today is a relatively modern affair (see the bucolic print below, from 1776) and Robin Hood is a brand more than anything else. However, the inquisitive will find evidence of real history that is far more tangible – centuries of excavation into the sandstones beneath the city.

I remember as a kid the famous “Trip to Jerusalem” pub and its rooms and caves carved back into the rock; and the history of the city’s caves came with all the dire, dark, and bloody stories that kids love – dungeons and death, mysteries and evil-doing. Evidence of the subterranean maze can easily be seen from the outside today, entrances in the cliffs frustratingly closed by locked doors and metal grills.

 
This man-made cave system, space hewn from the rock, has developed over the centuries because the sandstone is relatively poorly cemented and easily excavated. At least since Mediaeval times, tunnels and rooms have been carved out for a vast array of purposes, including dungeons, beer cellars, cess-pits, tanneries, malt-kilns, houses, wine cellars, tunnels, summer-houses, air-raid shelters, sand mines, follies, dovecotes and, for while during WWII, the storage of radium. Temperatures underground remained constant and cool, making for ideal conditions for brewing and storing ale – the Mediaeval malt kiln below is an example of the year-round brewing facilities that made Nottingham famous for its beer (a reputation sadly much-diminished).

 
The known extent of this subterranean infrastructure probably only represents a fraction of the entire system, and now a project to survey and map the caves is well-underway, superbly documented on the project website - “The Nottingham Caves Survey is the first part of the Caves of Nottingham Regeneration Project (CoNoRP). This is a two-and-a-half year project funded by the Greater Nottingham Partnership, East Midlands Development Agency, English Heritage, the University of Nottingham and Nottingham City Council. The project intends to take a fresh look at Nottingham’s caves and encourage the City and its visitors to appreciate the caves for the unique historical resource they are.” The survey is based around the wonderful technology of 3D laser scanning, described on the website:

Laser scanners come in a variety of forms but they all work in a similar way. The scanner fires out a beam of laser light which reflects back from the first thing it hits. The instrument measures the amount of time it takes for the light to return, and from this can calulate how far away that object is. The scanner then rotates the beam a little, and takes another measurement. It continues to rotate vertically and horizontally until it has taken measurements in a 360-degree horizontal circle and usually a 310- degree vertical circle. All the measurements are accurate to around +/- 2mm. From these measurements we have an almost complete 3D survey of a cave. What makes this technology really exciting is the speed at which modern laser scanners work - up to 500,000 survey points per second! The resulting ‘cloud of points’ can be connected to adjoining scans to produce complete surveys of cave systems. Once downloaded into the processing software we can do lots of different things with the point cloud data - make simple sections and plans, elevation maps and isometric images, fly-through videos, explorable .mov images, TruView web delivery, and virtual or real models. Because of the accuracy of the survey data, it can also be used for monitoring the caves. We can go back and re-survey a cave after a year or a hundred years and see exactly how and where it has changed.

And the results are dramatic. The strange image at the head of this post is laser-scanned orthographic plan of the Peel Street caves, Nottingham’s largest cave system and a sand mine that was excavated between 1780 and 1820. Here’s an example, showing the caves in the Castle Rock, including the infamous “Mortimer’s Hole,”  Brewhouse Yard caves, and “Ye Olde Trip to Jerusalem Inn” caves (click for full-size image).

The images are stunning, and, on some of the high resolution versions available on the project website, you can begin to see the sedimentary structures:

 
So where did these accommodating sandstones come from? In the UK, they are part of the appropriately named Sherwood Sandstone Group, the outcrops around Nottingham being originally named the Bunter Sandstone; essentially all of them are red. They were deposited in desert and fluvial environments during the Triassic Period a couple of hundred million years ago, and their structures, including beautiful cross-bedding, record flash floods and blowing sand:

 
These photographs, courtesy of Ian West at the University of Southampton, come from the south coast of England where the Triassic Sherwood Group inevitably underpins the Jurassic Coast World Heritage Site. For the Sherwood Group, along with whatever its local equivalents may be in local nomenclature, extends across the UK and into the rest of Europe. The sandstones are often, as they are in Nottingham, poorly cemented and porous and can make excellent reservoirs for water and for oil and gas. But the Triassic sands don’t stop on the south coast of England – they can be found, in all their red glory, down the east coast of North America, where they preserve the first dinosaur footprints ever found (by the wonderfully named Pliny Moody working on his father’s farm in Massachusetts in 1802) and provide the building stone for New York’s iconic brownstones.  

These rocks formed as the supercontinent of Pangaea disintegrated, rifted apart to leave the testaments of red sandstone separated by the Atlantic Ocean:

Therein lies a story that links the mediaeval troglodytes of Nottingham with the Battle of Gettysburg – but that’s for another day.

 

[Thanks to Geoff Manaugh at his ever-fascinating BLDGBLOG for alerting me to the story of the Nottingham cave survey. Nottingham images from the caves survey project website.]

 

Sunday sand: a nuptial arena

 
This last summer, the wedding of the daughter of friends of ours took place on North Stradbroke Island, off Australia's Queensland coast. A dazzling expanse of dunes and beaches, it’s considered to be the world’s second-largest sand island (a quick quiz, no prizes – what’s the largest? Hint: it’s not too far away). It’s only natural that sand contributed to the memories of the nuptial event, and that a sample of such would fall into my hands, almost pure quartz, the grains sparkling with a subtle range of hues and shapes.

 
It’s tempting to view North Stradbroke as a barrier island, but it probably isn’t. The core of the island is made up of old sand dunes that were reworked and redistributed as sea level rose and fell during the ice ages. This process goes on, dramatically and dynamically today, the coastal area and swirling offshore sand banks constantly shape-shifting with time, the seasons, and storms. Indeed, the island only became an island little more than a hundred years ago as a result, it would seem, of a strange conspiracy of circumstances. In a storm of 1895, a Scottish ship carrying (what else?) whisky and dynamite, was wrecked on the narrow strip of sand that then connected what is now the island to the coast to the south. The whisky was, of course, salvaged, as was the dynamite which was stacked up in the dunes and intentionally detonated. The explosion caused some considerable damage and destroyed much of the vegetation holding the sand together, and the next major storm ripped into the beach and opened up the Jumpinpin Channel. A little time playing around with Google Earth historical imagery will demonstrate the ongoing dynamics of the sands around the channel which is steadily migrating northward; an entertaining documentation of coastal change, together with old maps and shipwreck legends,can be found here.

So, a long-lived and spectacular playground of sand; but, along with the attractions come problems, for, amongst the old dunes, the natural processes of winnowing and segregation have produced placer deposits, concentrations of grains whose mineralogy is of commercial interest. For sixty years or so, the sands of North Stradbroke Island have been mined for the minerals rutile, zircon, and ilmenite, concentrated in these placer sands. Rutile is primarily titanium dioxide, and ilmenite is an oxide of iron and titanium, and so these minerals are a source of titanium metal, but, even more importantly, its oxide, which is the base for multiple applications as a white pigment. Your skimmed milk may be thus whitened and your refrigerator may owe its brilliance to North Stradbroke Island.

But sand mining is an unsightly business, conducted on a huge scale: around 50 million tonnes of sand are mined each year to produce 500,000 tonnes of minerals.

 
The State Government now has a plan (not without controversy because of the economic and employment implications) for closing down the mining operations and turning more than half the island into a State Park by next year, and 80% by 2027. Details of the plan and the controversy can be found on Queensland Government website and in articles from the Sydney Morning Herald and the Courier Mail.

 
As is so often the case, the tensions between commerce and communities, landscapes and livelihoods, result in a complex of grey areas for policy-makers to work through. But it is certainly inarguable that North Stradbroke Island’s sands create a stunning and unique landscape, worthy of our respect and preservation.

 

 

Sand and ice 2: sorting out a glacial mess

Those folk who have had the pleasure (dubious, at times) of wandering around the front of a glacier know what a mess the place is – hardly an ideal campsite, but then necessity, as I can attest, can be a mother.

Glaciers are mighty combinations of bulldozers and conveyor belts on a massive scale, scouring the landscape and transporting huge volumes of carelessly jumbled debris: boulders, pebbles, gravel, mud, and, of course, sand. Only when the ice melts do the streams of water begin to sort things out; but they can do this quite efficiently, and significant sources of high quality aggregates, sand and gravel, owe their origin to the processes going on as glaciers retreat (I’ve written earlier of how the glacial sands of Long Island built New York). But those processes are complex and varied, and leave behind a chaotic landscape, a topography filled with arcane terms – eskers, kames, drumlins, and kettles. But hidden within that chaos are the geo-clues that, if examined carefully, provide the forensics for reconstructing the retreat of the glaciers. And it is this kind of detective work that is the subject of the second in my thematic miniseries, “Sand and ice.” As I described in episode 1 last week, a random selection of two journals from the stratigraphic pile of reading-to-catch-up-on provided this theme, the second one being from The Proceedings of the Geologists’ Association. In the latest issue, Stephen Livingstone and his colleagues at Durham University tell a meticulously documented story of how an area of Cumbria, known to the cognoscenti as the Brampton kame belt, records the last retreat of the British-Irish ice sheet ten to twelve thousand years ago.

 
The ice sheet in this region retreated westwards, away from the uplands of the Pennines and the Lake District, eventually leaving behind, as sea level rose, the landscapes of the Solway Firth and the surrounding lowlands. As the ice retreated, all the geological rubbish that was carried on top of the glaciers, trapped within them, contained in meltwater channels below them, and transported by rivers in front of them, was left behind, dumped. The landforms that result can be referred to as glacial karst. This was not a term that I had encountered before, thinking of karst only as the dramatic limestone scenery that results from the collapse above dissolved cavities and large cave systems. But that process of solution and collapse occurs as a glacier melts – except that the solution is the melting and disappearance of the ice. Among the strange topography that results, are kames - “steep-sided, variously shaped mounds composed chiefly of sand and gravel, formed by supraglacial or ice-contact glacifluvial deposition.” These landscapes often show topographic inversion – in other words, what was once a low point is now high, and vice-versa. Think of a lake forming in a depression on top of a glacier, and visualise that lake being filled with sediment carried into it by meltwater and flowing from collapsing moraines; imagine then what happens when the glacier disappears. The pile of lake sediments are undermined and will subside and be deposited on what was the land surface below the ice and form a hill, a kame – a topographic high. It’s this kind of process that formed the jumbled topography of the Brampton kame belt.  

The approach that Livingstone and his colleagues have taken is simply a classic, elegant, piece of geological work, putting together and meticulously documenting, the pieces of the puzzle. The land today is covered in farms, villages, and vegetation, but high-resolution radar imagery provides an uncluttered view of the landscape for detailed mapping. Boreholes provide data from the subsurface, but, most importantly, there remain a number of sand and gravel pits in the area, some of them still active. These provide three-dimensional views of glacial rubbish dumps:

  The paper describes how the authors defined a series of lithofacies associations (LFA) from these spectacular exposures. A “facies” is the collection of characteristics of a sediment that are diagnostic of the environment in which that sediment was deposited. In broad terms, the sands of a beach will be different from those of a river bar, but the diagnostic distinctions of different facies are far more subtle and detailed than that. “Litho” simply means that the facies are defined by sediment character (grain size, structures, and so on), rather than including biological or fossil evidence. And associations means that two  or more facies are commonly found together and jointly contribute to the environmental diagnosis. So, having got the jargon out of the way, here’s the kind of detailed depiction of what can be seen in two faces of the aggregate pit shown above (best to open up the full-resolution image in a separate tab in order to see the detail).

 
All this data is collected from observations over just 15m vertically, and perhaps 30m horizontally; the illustration shows the spatial distribution of the different sequences of sediments, the grain size and internal structures (ripples, for example), and the relationships between underlying and overlying beds – all of which lead to the definition of three distinct LFAs. These sediments are interpreted as having been deposited in complex river (fluvial) systems flowing across the debris-strewn “dead ice” of the melting glacier. The paper references modern-day analogues from Iceland for the lithofacies associations – in the middle photograph below, this kind of “dead ice” can be seen in the banks of a lake set in the midst of the dynamic sedimentary chaos on top of a melting glacier.  

 
In the walls of the Brampton sand pits, there is further dramatic evidence of subsidence as the ice beneath piles of sediment melts: faults. In the lower right photo of the exposures, above, there are beautiful miniature faults cutting across the beds, formed as the pile of sediments collapsed.

This kind of approach is documented from boreholes and other sand pits, and the paper concludes with a description of the sequence of events that leads to the development of these complex landscapes of glacial karst and topographic inversion (ah, one other piece of terminology – diamicton refers to any sediment that contains a wide range of grain sizes, from boulders to mud, generally glacial in origin and otherwise known as till) :

I enjoyed this work as the second episode of my miniseries on sand and ice, and I hope that I have conveyed its classic and meticulous approach. It’s a great illustration of how careful examination of the sedimentary record (and, of course, the testaments of sand in particular) help us understand our surroundings and the landscapes of our planet. I’ll leave you with a couple of stunning photographs of glacial sediments from the Open Geoscience site of the British Geological Survey:

 

[The full reference for the Livingstone et al. paper is: The Brampton kame belt and Pennine escarpment meltwater channel system (Cumbria, UK): Morphology, sedimentology and formation, Stephen J. Livingstone, David J.A. Evans, Colm Ó Cofaigh and Jonathan Hopkins, Proceedings of the Geologists’ Association, 121 (2010), 423-443. This was first published online in 2009, but unfortunately is not open access. However, Livingstone’s doctoral thesis, “Reconstructing ice dynamics in the central sector of the last British-Irish Ice Sheet” is available in its entirety (all 119 mb!) online at http://etheses.dur.ac.uk/195/. The image at the head of this post of kames in the proglacial area of Virkisjokull, Iceland is from the BGS image collection.]