Yesterday's News & Observer got from its staffer Kerstin Nordstrom an engrossing tale of technical climbing and geological mystery that is playing out in one of the nation's foremost national parks. The story is also hobbled by some over-simplifications and errors, but not enough to cipple it.
The news is that a UNC grad student and his professor are taking advantage of the former's technical climbing skills to painstakingly sample the sheer granite monolith that is El Capitan, a 3000-foot-+ monster of almost vertical walls in Yosemite Valley. Visitors often put binoculars on the thing and are surprised and sometime terrified-by-imagining-themselve-there when they see people climbing slowly toward the top, hanging on ropes and spending nights sleeping on a ledge or even suspended and swaying in their sleeping bag 'portaledge' platforms - like spiders' egg sacs - over the abyss.
It captures well the dedication and adventure than can occur in scientific research. It tells of the mystery of the formation processes of such towering stones as this. The valley of the Yosemite is a welter of granite and granodiorite plutons. El Capitan is the largest. Plutons form in the Earth's crust where blobs of magma rise near but don't reach the surface, cooling and crystallizing. Nests of them are called bathyliths, multi-unit igneous complexes that may be scores to hundreds of miles across. The UNC effort aims, it says here, to scrutinize the detailed crystal distribution and trends on El Capitan's face. That may help choose between two competing hypotheses - which Nordstrom calls theories - of the exact sequences of injection and cooling that form such things. She calls one the blob theory. The only technical term I can find that fits the bill (yes, wikipedia) is 'Stokes Diapir.' Blob theory works for me.
So the story has color and sweep. The faults are in the details. She calls it the largest chunk of granite in the world. Hmm, there must be bigger plutons somewhere, maybe in the giant Idaho bathylith,that are bigger but perhaps still unrevealed by the sort of erosion that has Yosemite's plutons including this one and half dome standing tall. The park's website asserts that El Cap is the worlds largest granite monolith. A monolith is something that rises above its surroundings, a natural obelisk or other edifice. Simplifying that to largest chunk, period, is no biggie but still a fib.
Other problems, and this is mostly off the top of my head so I might we wrong on some scores but probably not all: The story recounts the tectonic setting, a subduction zone, that led to the batholith and its plutons. It says conditions were extreme, "temperature in the thousands, pressure thousands of times atmospheric pressure." Well, hot felsic magmas may be more than 1000 C, or about twice that in F, but that's not many thousands. And pressures in subduction zones are no higher than they'd be under any other conditions at the same depth - maybe less, as felsic rock is not particularly dense. So there's nothing special about their pressures. Magmas in such places are not necessarily molten material from under the crust as the story implies - they often form in the crust. Finally, I'm unsure that glacial carving had a lot to do with the sheer walls and overall shape of Yosemite's monoliths - the granite monoliths of tropical Rio de Janeiro such as Corcovado and Sugarloaf are comparable but coped with no glaciers.
Finally, and not to pile on, the molten predecessor to granite may indeed be a mineral soup, sort of, but iron and magnesium are not minerals. They are elements. The soup was more elemental than mineral. It would also have included such elements as aluminum, oxygen, potassium, silicon, sodium. Those are not minerals either. When it cooled the elements formed many minerals: feldspar, plagioclase, biotite, hornblende, quartz, mica, etc. None of those gets mention.
It's nonetheless a useful story. It blends one person's distinct skills and enthusiasms with the scientific quest to explain the world around us. It is told in an engaging way that will leave readers with a sense, if not an understanding, how science can be done. It also serves as reason, after a draft nears publication, for a journalist to re-check its technical details with expert sources.
- Charlie Petit
