geology

Posted by Ellen

On Saturday morning, geophysicists believed Iceland's Bardarbunga volcanic system had begun erupting beneath the huge glacier that hides it from view. By Saturday evening, however, new data or new interpretations of the data were raising doubts about this conclusion; the magma might still be trapped in rock a few kilometers below the bottom of the ice.

The actual eruption might have already begun or might begin at any moment or might never happen at all. But Bardarbunga's magma is definitely on the move down there in the earth's crust, melting some of the rock in its path and shouldering the rest out of its way, along a northeasterly route tracked by literally thousands of earthquakes.

Halldor Eldjarn has set the earthquake data to music, which you can listen to in near-real time.

Posted by Ellen

At the north end of Castlepoint sheep station is Castle Rock itself, noted and named in the eighteenth century by Captain Cook. The rock anchors one end of a limestone reef; on the headland at the other end is Castlepoint Lighthouse, built in 1913, originally fueled by oil but now wired into the grid and controlled from a switchboard in Wellington, a couple of hours away. Its light is visible 22 miles out at sea.

The postage stamp above dates from 1947.  For almost a century beginning in the 1890s, the New Zealand government operated a life insurance company that had government franking privileges and printed its own stamps. Lighthouses were nineteenth-century symbols for insurance companies (as were big rocks, e.g., Mutual of Omaha). The government sold off its insurance operations in the 1980s, to a corporation doing business as Tower Life of Dunedin, New Zealand.

The reef at Castlepoint is not at all like the coral reefs growing placidly around tropical lagoons; geologically, it's a chunk of ancient seafloor millions of years old heaved up violently during seismic activity associated with the collision of the Pacific and Australian tectonic plates.

The limestone in the reef is richly fossiliferous, and directly underneath the lighthouse it's pocked with caves.

Inside the reef is a lagoon and a wide, hard-sand beach, crucial features in the development of a large sheep station here, back in the days before highways. Since the coast in this region has no natural harbors, sheepmen used to drive wagonloads of wool bales down the beach, to be loaded at water's edge into small boats that ventured out at high tide to meet up with cargo ships waiting offshore.

Today, shipping activity at Castlepoint is mostly recreational in nature, and the hard-packed beach now serves tractors and boat trailers. The blue tractor in the picture below is driverless and remote controlled from the boat, where the captain calls for it to push an empty trailer down into the surf and then pull the loaded trailer back up to high ground.

In the picture below, the tiny figure walking the beach near water's edge is my mother-in-law.

Posted by Ellen

All it took was a few days of bad weather like this, every year for maybe half a million years, and most of the sediment that used to blanket this part of South Dakota has washed on down the White River and then into the Missouri and the Mississippi and the Gulf of Mexico.

This was an ancient seabed, back in the day, deeply mucky, collecting sand and silt and mud from the Black Hills nearby and the Rockies beyond. The sediments piled up in layers hundreds of feet thick, but when the ancient sea drained and the lithified muck was exposed to the elements, wind and rain and frost proved to be powerful chisels. 

It's believed that in another half million years, the remaining spires and parapets will have crumbled down into the gullies, and it'll be curtains for the scenery hereabouts.

Posted by Ellen

It must have been Oscar Wilde who said that you could never be overdressed or overeducated. In fact, he may be saying it just now, as he contemplates the world outside his childhood home in Dublin's Merrion Square, dressed to the nines from the neck down and wearing a becoming shade of snark across his face.

Sculptor Danny Osborne was as much prospector as artist for this project. He found the jade for Wilde's smoking jacket in extreme northern British Columbia, near the Yukon border. The pink collar and cuffs are from manganese-rich veins of zoisite in Norwegian shale.

The shimmery trousers are larkivite, also from Norway, a coarse-grained rock rich in anorthoclase feldspar, mined in Oslo Fjord. The well-polished shoes are black charnockite, from southern India; they get their shine from a distinctive kind of pyroxene known as hypersthene.

The 35-ton boulder that Wilde lounges on is Irish, but it's not in situ; Osborne found it in the Wicklow Mountains outside of Dublin.

The statue was sponsored by the Guinness Ireland Group and dedicated in 1997, ninety-seven years after Wilde's death at age 46.

It seemed appropriate, even necessary, to end this posting with a Wildeism. Settling on a single passage, however, proved ridiculously difficult, and it is certainly unfair to the man to reduce him to well-dressed witticism. But this line may do as well as any: "Every saint has a past, and every sinner has a future."

Or this: "Being natural is simply a pose."

Posted by Ellen

Years of drought have drastically lowered the water level of Lake Abbe, along the border between Djibouti and Ethiopia in the Horn of Africa. Vast stretches of what used to be lake bottom are now exposed, including clusters of limestone formations like these, many of which are chimneys venting sulfuric steam.

The chimneys formed when the vents were underwater; heat from the steam caused minerals to precipitate out of the lake water and build up around the rims of the vents.

Lake Abbe is a salt lake, the lowest point of a desert drainage system that has nowhere to drain. It's full of steam and sulfur because it's probably the birthplace of a new ocean, a triple junction of spreading faults where three tectonic plates are being pulled relentlessly apart from one another. Two of the faults are already so deep that they are full of ocean water: the Red Sea and the Gulf of Aden. The third fault stretches south from Lake Abbe through eastern Africa as a chain of lakes and deep depressions: the East African Rift. 

Along these faults, tectonic plates are pulling apart from one another at rates approaching an inch a year, thinning out the earth's crust in the region, and generating much volcanic activity and gaseous emissions. The geologic evidence strongly supports the likelihood that someday the land around Lake Abbe will be thousands of feet underwater, near the middle of a big blue sea.

But it will take a while. Rifting began here about 60 million years ago. At current rates of divergence, the new basin is spreading roughly 10 miles every million years. In another 100 million years, we'll have an ocean about a thousand miles across.

The drought may (or may not) be over by then.

Posted by Ellen

Well, I didn't know there really was such a thing as the Big Rock Candy Mountain, but here it is, rising above a resort with the same name along Highway 89 near Marysvale, Utah.

Volcanic explosions, followed by magmatic intrusions, followed by twenty-odd-million years of erosion and hot-springs-type chemical interactions have streaked the mountain with colorful mineral deposits. The reddish rocks contain iron-based minerals, including hematite and pyrite, while the whitish rocks contain potassium-based minerals, notably including kaolinite, a valuable white clay used to make paper glossy for magazines or photos.

The mineralization of Big Rock Candy Mountain acidifies runoff water, leaving the soil here relatively inhospitable to vegetation. Nonetheless, ponderosa pine are hanging on, especially near the ridgetop.

It's hard to imagine that in the 1930s there would have been anything about this part of the world that was hospitable to hoboes, either. No lemonade springs, no lakes of stew and whiskey too, no cigarette trees, nothing but more of the longing and aching that inspired Harry McClintock's song.

Posted by Ellen

 

The sun was shining brightly on April 10, 2010, when a hillslide suddenly slumped down onto this highway near Keelong City in northern Taiwan.

The soil was dry. There was no seismic activity in the area. It was just one of those things.

Posted by Ellen

 

C-T scans have been in the news recently; evidently, they can sometimes be dangerous, zapping people with risky levels of radiation. My master's thesis involved a C-T scan, but fortunately a very safe one, of a rock instead of a human being. Rocks can sit there and take huge doses of X-rays without injury or complaint, making them ideal targets for this sort of procedure. Because there's no need for radiological restraint, scanning a rock can yield much clearer, more detailed results than scanning a live person. It's also a lot cheaper.

The rock I sent to Texas for a C-T scan was a metamorphic chunk of the North Cascades mountains in the state of Washington. It had garnets in it. Each garnet was surrounded by a shell of pure-white minerals: quartz and plagioclase. The rest of the rock--what we termed the matrix-- looked dark gray in color; it actually consisted of the same white minerals as in the shells, flecked with tiny black grains of a kind of mica called biotite.

We were trying to figure out why the garnets were set off from the rock matrix by the white shells, which we called coronas. Our hypothesis was that unusual conditions during the rock's metamorphism had permitted garnet growth but had simultaneously limited diffusion of elements that the garnets would consume during their growth. We wanted to know more about the geometry of the coronas, and about the separation between garnets and matrix. So we shipped a core of rock about an inch in diameter to a C-T lab at the University of Texas, where it was zapped with X-rays;  the results were reconstructed by a computer, rendered in 3-D, colorized, and made into a little animated movie.

I've posted the movie on YouTube. I recommend watching it--even if it's not your kind of movie, it only lasts 12 seconds. The garnets in the rock are rendered red, the corona shells green, and the matrix rendered as transparent, with a slight reddish speckling of biotite grains. When I first saw this movie, I'd spent months working with the rock sample, but I was surprised by how long and snake-like the coronas are, and how many clumps of garnets each corona engulfs. How did this happen? The short answer is that the rock got squished squished and heated and stretched and squished and heated again during its mountain-building experience, which coincided roughly with the era of the extinction of the dinosaurs. The long answer is published in a journal called Canadian Mineralogy.

And now, the rock is doing a star turn on the internet, in what I honestly believe to be the first true hard-rock video on YouTube.

Posted by Ellen

Early in the morning of June 19, 2002, the Landsat 7 satellite swooped across the Indian Ocean and snapped this picture of Reunion Island. The volcano there, Piton de la Fournaise, was quiet that day--the clouds in the picture are just clouds, passing by.

Geologically, Reunion is virtually a twin to Hawaii halfway around the world, a huge shield volcano above an oceanic hotspot. It has been one of the most active volcanoes in the world throughout modern history, erupting almost every year, sometimes more than once, since 1670. The whole island is made of basaltic lava; it's the tip of a volcanic monster mountain rising from the ocean floor. All over the island are volcanic vents, cones, craters, and large calderas, where lava domes exploded and collapsed. The caldera that is currently most active, toward the top of this picture, has slumped down all the way to sealevel at the coast.

Basaltic rock weathers to make rich soil, and here as in Hawaii the climate encourages lush vegetation. New lava doesn't remain bare rock for long.

Politically, Reunion is part of France; because of its time zone far to the east of Europe, the euro became legal currency here a few hours before it did anywhere else. Eight hundred thousand people live on the island.

Posted by Ellen

Tsingys. Which means: the kind of place where you don't want to walk barefoot.

We use the German word, karst, as a general term for tsingys and other less extreme landscapes carved by the chemical interaction of limestone and rainwater. Limestone is oceanic in origin, formed at the bottom of the sea from the shells of dead sea creatures. When tectonic forces thrust the seafloor up onto dry land, rainwater immediately begins chewing away at it, in a chemical reaction something like the vinegar-and-baking-soda volcano of an elementary school science project.

Monsoon rains have been attacking the Jurassic limestone bedrock of western Madagascar for millions of years, dissolving channels in the surface and opening up caverns underground. Eventually, as the caverns expand, the rock above tthem collapses, forming sinkholes. The sinkholes enlarge along fissues and underground drainage channels, eventually forming steep-sided  "solution valleys." The rains continue to eat away at the rock between the valleys, until all that is left is raggedy spikes. Tsingys.

It's so hard to get around in this landscape that the flora and fauna have yet to be catalogued. Even animals and plants have a hard time traveling here; they live in micro-ecosystems that have evolved in isolation from one another as well as from the rest of the world.

Ten percent of the earth's surface is karst, but most of it is too young or too arid to develop the extreme features of the tsingys. But all karst is evolving slowly or rapidly toward the kind of landscape seen here. It will be kind of a shame in a few million years when Florida gets to looking like this; who's going to want to visit beaches where you can no longer walk barefoot?