July 5, 2012 | 2
So, the National Trust of Northern Island unveiled a spiffy new Visitor’s Center for the Giant’s Causeway, one of the great geologic wonders of the world. There’s just one problem, I learned this morning, thanks to the Twitter feed of physicist Brian Cox. Apparently the Trust couldn’t just stick with the scientific facts; they had to be “inclusive” with a segment in one of the audio exhibits that mentions that certain evangelical Christians believe that the 60-million–year-old formation was actually the result of Noah’s Flood a mere 4500 years ago.
In response to a query by the National Secularist Society, a spokesperson for the National Trust offered this olive branch:
“The interpretation in the visitor centre showcases the science of how the stones were formed, the history of this special place and the stories of local characters. We reflect, in a small part of the exhibition, that the Causeway played a role in the historic debate about the formation of the earth, and that for some people this debate continues today. The National Trust fully supports the scientific explanation for the creation of the stones 60 million years ago.”
Um, great. You know, there is scientific fact, and there is personal belief fueled by blind faith; they are two very different things. People can and do believe whatever they damn well please, but that doesn’t make it fact.
Let me paraphrase a quote ascribed to Galileo when people objected to the Copernican solar system on Biblical ground: “The Bible teaches us how to get to heaven. It is not a scientific treatise on how the heavens move.” (Galileo actually cited Cardinal Baronius for the statement, “The Bible was written to show us how to go to heaven, not how the heavens go.”) Or as Cox tweeted: “I don’t mind creation stories presented as mythology, but to suggest there is any debate that Earth is 4.54 billion years old is pure shit.”
‘Nuff said. But it did inspire me to dig up a fun post from the archives about the geophysics of the Giant’s Causeway. Because I’m guessing the National Trust also included the wonderful Legend of Finn McCool.
Irish legend is rife with memorable characters, among them a giant named Fionn mac Cumhaill — or, more colloquially, Finn McCool. As with all myths, the details vary but the essence of the tale is this. Finn McCool lived on the north coast of Ireland with his wife Oonagh.
One day his rival, the Scottish giant Benandonner began taunting him from across the channel — the usual “I’m bigger and tougher than you, little wuss-boy” macho drivel, no doubt accompanied by much beating of chests and flexing of biceps. (Clearly Benandonner was a wee bit insecure, perhaps because he didn’t have a catchy moniker like Finn McCool.)
Put bluntly, Benandonner said he could kick Finn’s ass if only that pesky channel wasn’t in the way to stop him. No self-respecting giant would stand for that insult to his masculinity. So Finn called his rival’s bluff, and built a causeway (bridge) out of huge stones across the water, since no boat at the time was large enough to hold a giant. And he invited Benandonner to come right on over and prove his point.
The variations diverge at this point, with some versions saying Finn merely wanted a chance to rest before the confrontation, after exerting so much energy to build the causeway, and others claiming he was frightened when Benandonner loomed into view and he realized his rival was indeed the bigger, stronger giant. (I’m inclined to favor the latter.)
Finn’s wife Oonagh was smarter than either male giant; she knew that battles aren’t always won on the basis of size and strength. She suggested stealth. She disguised her husband as a baby in a large nightgown and bonnet — possibly even a supersized rattle — and placed him in a gigantic cradle.
When Benandonner arrived, she invited him in for tea and asked him to be quiet so as not to wake the “baby.” Benandonner took one look and decided that if this enormous creature was Finn McCool’s infant, he had no desire to meet the father, and fled home to Scotland, ripping up the causeway behind him to ensure Finn McCool couldn’t follow him. (Jen-Luc Piquant thinks this proves they were both pathetic girly-men, for all their tough talk and macho posturing.)
The remnant of Finn McCool’s legendary bridge is still there, in what is now County Antrim in Northern Ireland. It’s called the Giant’s Causeway, and is considered one of the seven wonders of the United Kingdom. Justly so — it consists of nearly 40,000 interlocking basalt columns, some as tall as 36 feet. The tops of the columns form “stepping stones” leading form the foot of the cliffs before disappearing under the sea. I’ve had the privilege of standing on those columnar formations in person, during a visit to Northern Ireland many years ago, and they’re pretty damned impressive.
Finn McCool is just a legend, on a par with the American giant, Paul Bunyan, dreamed up to explain how such a bizarre formation like the causeway ever came into being in the first place. It looks far too regular in terms of its patterned structure to have been caused by natural processes.
And yet it did. First “discovered” in 1692 by the then-Bishop of Derry, Sir Richard Bulkeley II officially announced the causeway’s existence in a presentation before the Royal Society of London, of which he was a member.
(Historical sidenote: There’s little record of Sir Richard II — a Google search yielded plenty of information about his father, but little about the son, who left no heirs and was therefore the last scion of that particular baronetcy. He was apparently deformed, but well-educated, a fellow of Trinity College and at Oxford, and in addition to his paper on the Giant’s Causeway, he also presented papers on a self-propelling chariot of his own invention, and a scheme for improving Ireland by cultivating the planting of maize. Alas, he succumbed to religious fervor in his dotage, falling in with a cult of self-proclaimed French prophets whom he believed would cure him of his deformity. They didn’t.)
Theories abounded as to how the causeway had formed: some said men had made it with picks and chisels, and of course, there was the legend of Finn McCool. The scientists were inclined to favor nature but were mystified as to the mechanism until 1771 when a Frenchman identified only as Demarest announced that it was the result of volcanic activity. (There’s even less Google-info on Demarest than there is on poor Sir Richard II.)
That’s still the accepted explanation, although it’s continually being refined as science progresses. The columnar joints that make up the causeway were formed roughly 60 million years ago by the cooling and shrinking of molten lava from a massive volcanic eruption.
According to physicist Lucas Goehring of the University of Toronto, who presented a paper at the 2007 APS March Meeting on his work with fellow Toronto colleague Stephen Morris, this is what probably happened. When the lava flowed into the sea, it quickly cooled, contracted, and crystallized into the near-perfect hexagonal columns we see today. In fact, geologists believe there were three major lava flows, giving rise to lower, middle and upper basaltic layers, with the causeway columns occurring in the middle layer. That kind of shrinkage inevitably causes stresses that fracture the rock.
Per Goehring: “The columns are formed as a sharp front of cooling moves into the lava flow, assisted by the boiling of groundwater. As the front advances, it leaves behind a crack network which evolves into an almost hexagonal arrangement. This network carves out the columns.”
Similar structures can be created with a simple kitchen experiment: mix equal parts corn starch and water and place into a coffee cup. Dry the mixture by shining a bright light above it. Within a week or so, the mixture will be completely dry and you can break it apart to reveal an interior that is broken up into “starch columns.” You can see a short video clip of their corn starch experiment here.
In addition to studying the genuine article in situ in both Ireland and Scotland, Goehring and his cohorts have figured out how to control this tabletop kitchen experiment so precisely that they can study the formation process in much greater detail than scientists could in the past, augmented by X-ray tomography to give the first genuinely 3D imaging of the internal structure of the columns.
Among the more surprising findings: (1) the columns are not quite as perfectly hexagonal as previously believed, and (2) the continuous dynamics of the formations can be found even deep inside the structure, similar to, say, dry foams. Also, the size of the columns depends on the speed at which the cracks advance, and the rate at which the water can move through the starch. That’s why lava-formed columns are 1000 times larger than the tabletop experiment: the analogous properties of lava are much slower.
Columnar joints are more common than one might think: they are also found at Devil’s Tower National Monument in Wyoming, at the “Organ Pipes” formation on Mount Cargill in New Zealand, and at the Devil’s Postpile National Monument in California. Ice can also make interesting formations, according to Meredith Betterton of the University of Colorado, Boulder.
Betterton became enthralled by the large icy spikes — called penitentes because they resemble a procession of white-hooded monks — she observed while viewing glaciers in the Andes. “I thought, ‘Wow, what’s going on here?’” she admits, and being a scientist, she set about figuring it out.
(She’s not the first to be thus fascinated. Charles Darwin described penitentes in 1839, while relating a March 1835 excursion in which he squeezed his way through snowfields covered in penitentes on the way from Santiago, Chile, to the Argentine city of Mendoza.)
Along with colleagues at the Ecole Normale Superieure in France, Betterton created the first artificial versions of these spiky ice formations, which can be found quite frequently on high-altitude glaciers where the air is particularly dry. She also devised a mathematical model to predict the process. The hope is that this research will yield useful insights into how glaciers evaporate; it may also lead to a practical strategy for preserving glaciers in light of global warming.
There’s probably a fascinating legend somewhere on a par with Finn McCool to explain how these spikes of ice form, but science is more than capable of stepping with its own explanation. Penitentes arise when the sun’s rays evaporate snow in such a way that the ice turns directly into water vapor, without melting into water first. The process is called sublimation.
The snowy surface might start out smooth, but it gradually develops depressions as some areas sublimate faster than others, and the resulting curved surfaces concentrate more sunlight and speed up the sublimation even more, leaving behind a forest of towering spikes of ice. Penitentes are nature’s ice sculptures.
Rising temperatures slow the formation of penitentes quite a bit, an especially alarming factor in light of global warming, because fewer ice spikes could accelerate the melting of glaciers. The spikes cast shadows, you see, and serve as a natural cooling mechanism. There’s a working hypothesis that spreading a small layer of dirt over glaciers could help preserve them by fostering faster formation of penitentes.
This turned out to be true with the small-scale versions Betterton created in her lab. She spread printer toner on her artificial snow layer to simulate pollutants common to glaciers around the world, and found that the ice spikes grew more rapidly as a result. It’s a bit counter-intuitive, since carbon-based pollutants actually increase melting rates on glaciers because the ice absorbs more sunlight and therefore heats up more quickly. The formation of more penitentes could offset that damage.
Not that Betterton thinks she has all the answers now about the mechanisms behind penitentes — not by a long shot. “There’s lots of things not yet explained, and that’s what makes this field so fascinating,” she said. But I doubt it has anything to do with Irish giants or Noah’s flood.
An earlier version of this post originally appeared at the old Cocktail Party Physics archived blog on March 6, 2007.
Images: (top) Giant’s Causway, Northern Ireland. Credit: Petr Brož. Source: Wikimedia Commons. (center) A View of the Giant’s Causeway: East Prospect. 1768 engraving by Susanna Drury. Public Domain.Source: Linda Hall Library of Science, Engineering, and Technology. (bottom) Field of Penitentes on the Upper Rio Blanco, Central Andes of Argentina. Credit: User:Arkavi. Source: Wikimedia Commons.
Betterton, M. D. (2001) “Theory of structure formation in snowfields motivated by penitentes, suncups, and dirt cones”, Physical Review E 63(056129).
Darwin, Charles. (1839) Journal of researches into the geology and natural history of the various countries visited by H. M. S. Beagle, under the command of Captain Fitz Roy, R.N., 1832 to 1836, H. Colburn, London.
Drake, Stillman. Discoveries and Opinions of Galileo. New York: Doubleday Anchor Books, 1957, pp. 173-216.
Goehring, Lucas, and Stephen W. Morris, (2005) “Order and disorder in columnar joints,” Europhysics Letters, 69, 739.
Goehring, Lucas, Zhenquan Lin, and Stephen W. Morris, (2006) “An Experimental Investigation of the Scaling of Columnar Joints,” Physical Review E 74, 036115.
Goehring, Lucas, and Stephen Morris. (2008) “Scaling of columnar joints in basalt,” Journal of Geophysical Research, Vol. 113, B10203, 18 PP., doi:10.1029/2007JB005018.
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