Who’s Interested in Some Geogallivanting?

Summer adventuring season is almost upon us! Lockwood and I will be doing an epic trip to the Josephine Ophiolite next week, and hopefully later this summer we’ll make it to the John Day Fossil Beds. I had a coworker prodding me about those the other day. You know, I love it when folks get all up in my face asking about things I’m woefully ignorant about, because then I’m all like, “Right! Field trip!” or get heavily involved in research, and I adore that.

You know what else I love? Proving to people they’re smarter than they think. Also, showing them things that make their eyes pop wide.

Moi with maclargehuge glacial erratic on Whidbey Island. Photo snapped by Cujo359.

Moi with maclargehuge glacial erratic on Whidbey Island. Photo snapped by Cujo359.

So that’s why I’m saying I think it’s time to take a few of you out in the field. You know you wanna! If you’re in the area or will be coming by this summer, why not spend a Saturday or Sunday poking round the local geology with me? We’ll have good food and good fun and in some places can even bash on a rock or two.

If any of you are interested, let me know, and I’ll get some schedules worked out. We could have a few day trips, possibly even an overnight or two, depending on what you’re up for. I’ve got a few ideas of the places we could go. If you think of others, bung ‘em in the comments, and we’ll see what we can do.

I’d love to go geotripping with you!

Moi demonstrating wind direction on an Oregon dune. You, too, could watch me do silly stuff for science! Photo shot by Lockwood.

Moi demonstrating wind direction on an Oregon dune. You, too, could watch me do silly stuff for science! Photo shot by Lockwood.

Can’t make it? We’ll take enough photos and post enough delicious detail that you can be there with us vicariously. I won’t neglect you!

A Personal Post from Karen

I have a cousin by marriage — we’ll call her Mary for the sake of this post, not her real name.  She has lots of health issues, though the most dire one is bipolar disorder.  It keeps her from holding down any sort of job.  She’s married to a guy who has troubles of his own, and is often on disability.  Family members say he’s amazingly lazy; I only met him once, at their wedding, so I can’t say.   But they definitely have trouble making the rent AND eating.

I suggested she put up a web page (another relative, who runs a small ISP, will host one for free), explain the situation, and put up a Paypal donate button.  I, and I suspect many of her friends, would be glad to sign up for small Paypal subscriptions.  I got no response.  Perhaps she’s having a “down” episode.

I want to help Mary help herself, but I don’t know how.  She does fantastic things when she’s “up”,  and struggles mightily when she’s “down”.  She does take meds, but they don’t seem to help much.

So I ask you, readers of this fine blog, for suggestions.

Thanks, Karen

The Real Heart of the Ocean

One hundred years ago*, a ship sideswiped an iceberg on its way across the ocean, and the Titanic legend was born. Speaking of legend, James Cameron’s film was so sweeping and dramatic that some folks think it must have been entirely fictional. But it was based on a true story, right down to the Heart of the Ocean.

The Love of the Sea. Sapphire and diamonds set in platinum. Photo reproduced here with the kind permission of the Nomadic Preservation Society.

Only, the real Heart of the Ocean wasn’t a blue diamond. It wasn’t heart-shaped. It wasn’t ever owned by Louis XVI. And it wasn’t called the Heart of the Ocean, although it’s now known as The Love of the Sea. There’s definitely a love story involved, though. Not to mention, geology.

This lovely and simple sapphire graced the neck of 19 year-old Kate Florence Phillips, a Worcester, England shop assistant eloping to America. Henry Samuel Morley, twenty years her senior and owner of one of the shops she worked in, had given her the necklace before they embarked on a new life together. They boarded as Mr. and Mrs. Marshall, with second-class tickets and likely first-class dreams. Henry had left his wife and child provided for. In San Francisco, he and Kate were to begin anew. One can imagine her face, glowing with happiness, with the necklace that symbolized their future glittering on her chest during dinners in the Titanic’s elegant dining rooms.

Then came the iceberg, and the reality of too-few lifeboats, and women-and-children first as the band played and the passengers scrambled to survive. Henry died in the icy Atlantic waters. Kate made it off the ship and back safely to England on the Celtic. She carried nothing but a purse with her trunk keys, a pregancy, and her beloved sapphire necklace.

That’s the human story of that deep-blue oblong. I, being a geology addict, am touched by their love story, but also by that beautiful necklace. What, when you come right down to it, is a sapphire? How did it form? And how did it end up nearly going down with arguably the most famous shipwreck in history?

It’s possible the Love of the Sea isn’t even a natural sapphire. The art and science of synthetic sapphires had emerged by 1902; ten years later, when Henry Morley went shopping for his new love and the Titanic sailed, over 7,000 pounds (3,200kg) of them were produced every year. But let’s assume that Henry was a true romantic and a gentleman who would have preferred a naturally-occurring gem. It’s more geological that way.

Crystal structure of corundum. Image credit: NIMSoffice at en.wikipedia.

I suppose it isn’t quite so romantic to point out that what he was purchasing was basically aluminum: aluminum oxide (Al2O3). It’s the crystalline form of aluminum oxide, which makes all the difference. This crystalline aluminum mineral is called corundum, and people have been wearing it with pride for thousands of years. It’s also a bonza industrial abrasive, and clear slices of synthetic corundum are used to make bullet-proof “glass.” Corundum is, in fact, the 2nd hardest mineral: a 9 on the Mohs hardness scale (if I ever open a restaurant, I’ll call it Mohs Diner). So Kate was wearing two minerals used on the hardness scale: diamond’s number 10. And you now have a new bit of cocktail party conversation. Accessorize accordingly.

A SUPERB, gemmy, doubly terminated sapphire crystal from Ratnapura, Sri Lanka. Ex Irv Brown TN Collection. Small, yes, but gorgeous riveting color! 1.6 x 0.5 x 0.4 cm. Image and caption credit: Rob Lavinsky, iRocks.com

A SUPERB, gemmy, doubly terminated sapphire crystal from Ratnapura, Sri Lanka. Ex Irv Brown TN Collection. Small, yes, but gorgeous riveting color! Image and caption courtesy Wikimedia Commons.

In its pure form, corundum is pretty much clear. Like so many things, impurities are what makes it fascinating. Ruby, the deep-red variety, gets its color from a trace of chromium. Padparadscha, a rather charming pink-orange gem, contains chromium, iron and vanadium. And sapphire, our gem of interest, can occur in a variety of colors from yellow to purple to true sapphire blue. The blue color is a result of traces of titanium and iron. But it’s not just down to trace elements: it’s about chemistry, too. That ocean blue is caused by a little thing called intervalence charge transfer. I wish I could translate that into plain English for you, but I have not yet studied enough chemistry to manage it. It’s got something to do with electrons. And it means that, while 1% chromium is required to make a ruby ruby-red, it only takes .01% titanium and iron to make a sapphire sapphire-blue. Neat, eh?

For an even better blue, sapphires can be heat-treated. Even the Romans did it. But the final oh in that deep, dark blue is OH, hydroxide. Sapphires with higher OH intensities have an almost TARDIS-blue hue. Less OH means a paler sapphire. My very own wee Montana sapphire, for instance, is probably low in OH, although I don’t consider it low in ooooh. Yes, I’m partial.

Sapphire from Madagascar. Image credit: Wikimedia Commons.

Sapphire from Madagascar. Image credit: Wikimedia Commons.

That was the easy stuff. “Here’s where it gets complicated,” as Amy Pond says. Because it’s not enough for me to know chemical compositions and why sapphires are blue (or purple, or yellow, or clear). No, I had to go and wonder, “How do these form, then?” I thought it would be a bit of a lark. You know, read a couple of papers about pretty things, breeze right through ‘em and be able to tell you precisely how sapphires begin and grow. By the end, a passing acquaintance with the geological dictionary had blossomed into an intimate friendship as I cried on its shoulder, and I’d decided a petrology course is most certainly in my future. Yeah. It gets that complicated. What follows is a super-simplified version.

A superb example of these strange sapphires collected in the mid 1990s by the Gochenour brothers, in Riverside County. This crystal is very aesthetically placed, and displayed in the matrix. These are significant and unusual big sapphire crystals for a US locality. Ex. Pala International/William Larson Collection. Image and caption credit: Rob Lavinsky, iRocks.com

The basic requirements for sapphire formation appear to be magma and country rocks rich in aluminum but poor in silica. You’ll find sapphires in some volcanic fields, and in metamorphic rocks like gneiss, mica schist and sometimes marble. Picture magma, that hot melty stuff. We begin with ultramafic and mafic melts, which is basically a fancy way of saying magmas that have very little silica and a lot of magnesium and iron. This hot rock rises, on account of being hot. As it ascends from within or near the Earth’s mantle, it’s going to encounter the country rocks – the locals, who were already chilling, probably lived there a while. Some of those country rocks have a low silica content, but lots of aluminum. As they get invaded by the hot stuff, they melt a bit themselves and mix in.

A gemmy, translucent, Sapphire cluster with thin hexagonal plates comprising a very sculptural specimen. Elegant, rare, and VERY appealing. A VERY RARE somewhat gemmy, translucent, SHARP, mogok sapphire. Most specimen sapphires are from Sri Lanka while in Mogok, rubies rule (it is “the land of rubies” after all!) 2.5 x 1.7 x 1.7 cm. Image and caption credit: Rob Lavinsky, iRocks.com

Now, different minerals start to crystallize out while magma’s underground. It’s a process called fractionation. It’s a fascinating process, and one we’ll explore in-depth someday. For now, it’s enough to know that some minerals crystallize out before others. Some of these minerals may very well be our very own corundum, with its trace elements. The whole process of creating sapphires is, judging from the abundance of “most likelies” and “mays” in these papers, still rather fuzzily understood. But we do know we find sapphires in basaltic lava fields or eroded remnants thereof, mafic dikes, places where granitic pegmatites interacted with silica-poor country rock, rocks formed by contact metamorphism (basically, where magma baked the country rock into something a little different), and in other metamorphic rocks. So we know it takes high aluminum content, low silica, lots of heat, mixing, and cooling to cook up a sapphire. Pretty much. And then they might be carried up to the surface by an eruption, or left quietly in place to erode out later.

Sapphires are buggers to extract from their native rocks, but they’re tough enough both physically and chemically to survive erosion, and so can be economically mined from sediments, especially stream deposits. They’re left behind when the lavas they grew in are weathered down to soil, where they can be recovered. And then the gem-quality ones are cut, polished, and end up as jewels that might, just possibly, get rescued along with their owner from a famous sinking ship. Lovely!

Sapphire crystals. Image credit: Wikimedia Commons.

Image Credits:

The Love of the Sea photograph reproduced with the kind permission of John White of the Nomadic Preservation Society.

All other images filched from Wikimedia Commons.

References:

Beran, A. and Rossman, George R. (2003): OH in naturally occurring corundum. European Journal of Mineralogy, v.18,N4, pp.441-446.

Coenraads, R., Sutherland, F. and Kinny, P. (1990): The origin of sapphires: U-Pb dating of zircon inclusions sheds new light. Mineral. Mag., 59, 465-79.

Srithai, B. and Rankin, A. (2006 ): Geochemistry and genetic significance of melt inclusions in corundum from the Bo Ploi sapphire deposits, Thailand. In Pei Ni and Zhaolin Li (Eds), Asia Current Research on Fluid Inclusion (ACROFI-I).

Charles Pellegrino: Ellen Mary Walker. Charles Pellegrino Website. Retrieved 4/14/2012.

Nomadic Preservation Society: Inspiring Jewellery Goes On Show… Retrieved 4/14/2012.

Want moar geology? Check out David Bressan’s post on the iceberg that sank the Titanic.

 

*Previously published at Scientific American/Rosetta Stones.

Superheroes and the Law

Okay, all you geeks, here’s a little something a damned good friend at work turned me on to:

Law and the Multiverse. Read it. Love it. Image filched from their blog for promotional purposes.

Law and the Multiverse. Read it. Love it. Image filched from their blog for promotional purposes.

Seriously. Law and comic book worlds. Law as it pertains to superheroes, supervillains  and other comic denizens. This is awesome. I’m a huge advocate of using stories and story worlds to teach other things. I learned a lot of my science and developed a burning passion for it partly through people who wrote books discussing the science of Star Trek. I learned to appreciate philosophy by reading essays by philosophers exploring the philosophy of Middle Earth and Batman. So why not learn a little law by reading what lawyers have to say about how laws would work in comic book universes?

Click the banner if you’re with me on that.

This is bloody brilliant, and I hope they turn it in to a book.

Geologists are Punny

Geologic language is very conducive to puns. It’s inevitable: you get two geologists together in the same room, they’re gonna let loose with some geo puns. It’s as certain as gabbro being called “black granite” by purveyors of quality countertops.

And we can keep it up past the point of reason. But we’re very gneiss about it.

geo puns

Blue: I like rocks! I am a nerd!

Black: likes this

Purple: Geology rocks.

Green: Don’t take it for granite.

Green: Shale I continue?

Purple: Of quartz.

Green: Igneous is bliss.

Blue: Wow! I love this convo! Thanks for being so gneiss.

Green: It was sedimentary, my dear Blue.

Orange: You’re definitely one of the boulder people I know!

Yellow: Groaning!!!!! lol

Red: Don’t let erosion wear you down!

Cyan: Oh Blue, if you weren’t such a dol-i-mite make more fun of you!

Purple: I gravel at your feet, master of puns.

That is made of epic win. There’s some in there I hadn’t even heard! I’d better start rocking it, or someone might bring the hammer down.

(Thank you, I’ll be here all week…)

Enough Cute to Make a Spartan Cry

No, I’m not going to show you what “this” is. I’m going to make you go look. It’s got to do with cats, ducklings, a shark, and a Roomba. You’re totally going to go look now, right? Swallow what you’re drinking first.

Right? That was hysterically cute. I shall now make it worse by bombarding you with more cute courtesy of the Daily Squee, I Can Has Cheezburger, and my own sick twisted sense of humor..

leonidas stop

ha ha no

lol

 

Nonsense Handily Diagrammed in a Variety of Languages

This is one of those things that every skeptic should have handy at all times. Happily, there are t-shirts (use the drop-down for a variety of styles, including women’s. Yay different styles and colors!).

Anyway, here’s the diagram:

Shamelessly filched from the Reason Stick.

Shamelessly filched from the Reason Stick.

 

 Visit the link, and you’ll find one in Croatian, one in Italian, one in Spanish, and another that includes conspiracy theories. I bloody love this thing! I’ve gone ahead and ordered one on a snazzy shirt. I’ll post a picture of me strutting round in it when I get it. Should I wear it to one of the local fundie churches and bring my Skeptic’s Annotated Bible? Or would that be too obvious?

New at Rosetta Stones: The Founding Mother of Modern Geology You Probably Don’t Know

We’ve got our next Pioneering Woman in the Geosciences up: Mary Horner Lyell. Yes, married to that Lyell. Some of you may not have known she was a fine scientist in her own right. It was hard finding information on her, but I did manage to draw together enough for a sketch, and I think you’ll like her quite as much as I do. Go introduce yourselves.

It’s Good to be a Skeptic

All of this is true:

what skeptics have

Aside from that wonder of birth stuff. Sorry, but I find it more icky than inspiring. What I do think is wonderful is that the squalling bundle of raw need that rips its way out of a woman kinda like something from Aliens ends up becoming a small mobile science question generator. I love it when kids reach that age where everything is wonderful and they want to know why. I love it when a few of them never lose touch with that child within them.

This is why things like creationism and “intelligent design” make me so angry. They destroy that sense of wonder. They hollow it out, and fill the void with bullshit. They destroy that child asking why. That, I cannot forgive them for.

Let the world fill with skeptics. Let wonder never cease. Let us never hear a “Because” without asking “Because why?”

Mélange et Trois: A Trip across Subduction Zone Madness

Few places on Earth are so full of geological mayhem as a subduction zone. Life in the interior of a continent in no way prepares you for the chaos you’ll encounter when seafloor dives under continent. Where I grew up on the Colorado Plateau, the geology’s like a lovely layer cake: nice horizontal slabs of schist and sandstone and sediments from ancient seas stacked neatly one after the other, with a volcano on top. Washington state is also like a layer cake: one that had a tiramisu jammed in with it, and some mystery dessert stuffed into the last empty space on the table, and then the whole table got caught in an argument between a steamroller and a bulldozer, leaving a jumbled mass only just barely recognizable as bakery products – with a volcano on top.

USGS geologists describe the rocks in the Chilliwack Terrane as “Highly folded and commonly upside down.” That’s one of the better behaved bits, mind. Some of the rocks in the Northern Cascades are so messed up that geologists can only describe them as a mélange – a mixture.

It’s madness. And in less than a hundred miles, I’ll show you some of the wildest crustal contortions you ever did see. We’ll go from a beach that has got deep ocean floor stuck atop it to a place 2,000 feet up where plutons of contentedly crystallizing magma endured the twice-baked potato experience. On our way, we’ll cross something on the order of eight different terranes, bits of crust that belonged elsewhere before they found themselves emigrating to America.

Ready for a wild ride?

Map of field trip area, Compiled from OpenCycleMap by Cujo359.

Map of field trip area, Compiled from OpenCycleMap by Cujo359.

 

Rosario Head, Fidalgo Island

 

We’re in medias res, here at this idyllic island beach. To the west, the Juan de Fuca Plate is busy piling up the Olympic Mountains. The Juan de Fuca’s a remnant of a remnant: two other plates met their demise in the Pacific Northwest before it. One of those plates, rammed against and beneath the North American Plate, plastered the lands we stand on to the edge of the continent. That plate, the Kula Plate, was responsible for most of what we’re about to see.

Rosario Head, Fidalgo Island, San Juan Islands

Rosario Head, Fidalgo Island, San Juan Islands

Have a walk along this tiny little beach on Fidalgo Island, and you’re walking across terranes. When I took the above photo, I was standing on the Decatur Terrane. The head is a knob of the Lopez Terrane. Just beyond Rosario Head, a short walk, you’re back on the Decatur again. Faults and folds have sliced, diced and twisted these rocks into a remarkable jumble. You’re looking at an anticline, actually, when you view Rosario Head. Think of it as the crest of a land wave: synclines are the troughs. The land around the Pacific Northwest is wavier than the ocean.

Let’s go stand on an anticline, shall we?

Folded ribbon chert atop Rosario Head. Author for scale.

Folded ribbon chert atop Rosario Head. Author for scale.

If you want to get an idea of the power of the forces at a plate boundary, note how contorted these rocks are. They’re ribbon chert, formed in a deep ocean environment from the silica skeletons of radiolarians. For ages, they lived their lives and died their deaths, drifting silently down to the seafloor, where time and pressure turned them to stone. You’ll find ribbon chert all over here, the quartz layers interleaved with slate. These layers were once happily horizontal. Now, they’re standing on end, folded and twisted.

It’s gorgeous rock.

Ribbon Chert, Rosario Head. Penny for scale.

Ribbon Chert, Rosario Head. Penny for scale.

 

A geologist could get lost up there for hours, and I did. Don’t be afraid to take a biologist along if you visit: there’s tide pools in the ribbon chert at the bottom of the head that will make them scream for joy.

If you tear yourself away from the ribbon chert, you can investigate pillow basalts, greywackes, and a nice icing of glacial till, all within a few hundred yards. You’re walking on the remnants of a volcanic island arc that’s 160 million years old if it’s a day, acquired by the North American continent, and then planed by an ice sheet that left behind a jumble of debris only a shade over ten thousand years old.

And if you’ve ever wanted to visit an ophiolite, congratulations! You’ve done just that.

Tear yourself away from the ribbon chert and tide pools. Up SR 20, across the Skagit basin, and into the mountains, we shall visit another island.

 

Limestone Quarry, Concrete, WA

 

We’ve gone back in time. Here, a coral reef flourished sometime in the Carboniferous, roughly 330 million years ago. We’re in another island arc, where volcanoes erupted and islands with their reefs formed, although this islands’s quite a lot older than the one we just visited. And it wasn’t really here: these rocks have been rafted in on a plate and scooted along faults to reach their present location, arriving sometime in the Cretaceous. This is the Chilliwack Terrane, that exotic block of land that inspired the phrase “Highly folded and commonly upside down.”

Folds in limestone, quarry in Concrete, WA. Quarry wall is roughly 100 feet (30 meters) high.

Folds in limestone, quarry in Concrete, WA. Quarry wall is roughly 100 feet (30 meters) high.

Those poor crinoids and corals had a rough time of it after they died. Their calcium-rich skeletons got mooshed into limestone so thoroughly that it’s hard to find a good fossil here, and then squashed into folds, which are easily visible in the quarry walls. And, insult to injury, their destiny was to become concrete. Hence, the name of the town. These little limestone lenses litter the Chilliwack Terrane, and in a land full of volcanics and metavolcanics, topped with yet more volcanics, they’re a delightful interlude.

Calcite crystals in limestone. Hand sample from quarry in Concrete, WA.

Calcite crystals in limestone. Hand sample from quarry in Concrete, WA.

You can find any number of calcite veins running through the rocks here, where water dissolved the calcite from the limestone and redeposited it. Some of it has turned some rather spectacular oranges and reds, which indicates there’s an iron-rich source of something around. But as gorgeous as some of those samples are, it’s a bit hard to concentrate on them. You see, there’s this view:

Mount Baker and Mount Shuksan from limestone quarry, Concrete, WA.

Mount Baker and Mount Shuksan from limestone quarry, Concrete, WA.

I told you there’s a volcano on top. From here, you can see it. Mount Baker is a result of the subduction of the Juan de Fuca Plate. To its right, you can see Mount Shuskan. Young mountain and old, volcano and uplift, all in one glance. Mount Baker is only about 100,000 years old, and, despite its peaceful appearance, is the second most active volcano in Washington. It would have been further to the east had the angle at which the oceanic Juan de Fuca Plate is subducting under North America hadn’t steepened.

Mount Shuskan is over a hundred times older. It formed when yet another terrane slammed into North America in the Cretaceous, about 120 million years ago, and is composed of metamorphosed oceanic basalt. This is what happens to quiet ocean floors when subduction grabs them: they can end up stuffed miles below the Earth’s surface, where they get cooked, then popped all those miles back up to an elevation of nearly 10,000 feet, high and dry.

And we’re about to see what happens to rocks that get deeply buried and then raised up as high peaks, although we won’t be personally encountering any more ocean floor.

 

Diablo and Ross Lakes

 

SR 20 takes you up and up, from what we in the West call hills (although in some regions, they’re mountains in their own right) and into a wonderland of sharp, towering peaks, with chains of lakes that don’t look like they were created by simple human beings damming the Skagit River.

Colonial Peak and Pyramid Peak from Diablo Lake Overlook. The extraordinary blue of Diablo Lake is caused by glacial sediments carried down by creeks.

Colonial Peak and Pyramid Peak from Diablo Lake Overlook. The extraordinary blue of Diablo Lake is caused by glacial sediments carried down by creeks.

We’re in the Metamorphic Core Domain now, standing on the Chelan Mountains Terrane. This area has been mountains more than once. As the Kula Plate collided with North America and terrane after terrane was plastered to the continent, great slabs of rock were thrust up. Magma stitched everything together, forming plutons more than once, which were then deeply buried and metamorphosed. The results are all around us here. Colonial and Pyramid Peaks are made of the beautiful Skagit Gneiss. If you’re a fan of banded and orthogneiss, this is your bliss.

Orthogneiss at Diablo Lake Overlook.

Orthogneiss at Diablo Lake Overlook.

Photos can’t capture how gorgeous these 60-90 million year old rocks are. The snowy white feldspar and quartz set off the glittering crystals of hornblende and biotite wonderfully. Everything glitters.

Those rocks testify to great masses of magma, which cooled underground and stitched newly-accreted terranes to the resident rocks. It might have been the weight of those masses that drove everything 20-30 kilometers (12-18 miles) down, where those granitic rocks got metamorphosed to orthogneiss. But that wasn’t the end of the story. About 45 million years ago, another episode of magmatism sent dikes of granitic pegmatite through the orthogneiss. You can see a magnificent example of this Challis Episode activity just across the road:

Roadcut through Skagit Gneiss. White streaks are granitic pegmatite dikes.

Roadcut through Skagit Gneiss. White streaks are granitic pegmatite dikes.

Things get rather hot in subduction zones.

Just up the road, you can also see evidence of how broken up things get when plates ram each other. Through all of these collisions, the crust has been folded, faulted, and fractured. As terranes got shoved over and under one another, bits broke off and went along for the ride. Things have been so thoroughly smashed up and metamorphosed that geologists find it difficult to figure out just what things used to be. Some of the gneiss and schist in these areas may have begun life as sedimentary rocks, but they’ve been so transformed it’s hard to know for sure. One thing’s definite, though: there were calcite-rich critters living in shallow seas, probably around volcanic island arcs, and their remains can be found down by Ross Lake, turned to marble.

Marble along the shores of Ross Lake.

Marble along the shores of Ross Lake.

You may have to get your feet wet to get a good look at it, but the cold dip is well worth it. There’s something about a rare bit of locally-grown marble that’s irresistible. This isn’t Michelangelo’s marble: it’s not that glowing creamy white, and it’s full of folds and fractures and evidence of a very rough life. But it’s ours, and we love it.

Coming down the trail to the lake, you’ve passed a fabric of orthogneiss and schist, cut with faults. We’re down in the Ross Lake Fault Zone, which marks the border between the highly-altered Metamorphic Core Domain, and the lightly-touched rocks of the Methow Basin to the east. Rocks have been scooted along this fault zone for tens of millions of years as movement along faults continued. Stand in the center of the dam, looking northeast toward Jack Mountain, and you’re staring at a stack of terranes piled up like so many bagels in a bag.

Jack Mountain from Ross Lake.

Jack Mountain from Ross Lake.

A thin slice on top, rising from left to right, is a bit of the Methow Domain’s Hozameen Terrane. Beneath it is the Little Jack Terrane, and then we’re back down on the Metamorphic Core Domain. Three terranes in one glance. One ginormous fault zone. Some truly outstanding geology, and we haven’t even gotten to the story of the modern Cascades yet.

The Kula Plate, followed by its sibling Farallon Plate, disappeared millions of years ago, swallowed up beneath North America. The Farallon Plate is still with us, in fragments: the Juan de Fuca Plate is one of its last gasps. As the Farallon broke up, and the angle of the subducting slabs changed, the edge of the continent warped. And with that warping came the mountains. They were born a mere five million years ago, and they’re still growing.

In a mere hundred miles, we’ve crossed hundreds of millions of years, at least five terranes, and barely seen a native North American rock. We’ve passed active volcanoes and walked on extinct island arcs. We’ve tramped ocean basins, reefs and plutons. The scenery here is dramatic: the geology even more so. We’ve only just begun to unravel the tangled history of the mélange that makes up one of the greatest geological stories on Earth.

Quite a trip, isn’t it?

Image Credits: Map of field trip area compiled by Cujo359 using data from OpenCycleMap. All photos by Dana Hunter.

References:

Brown, E.H. et al (2005). “Revised ages of blueschist metamorphism and the youngest pre-thrusting rocks in the San Juan Islands, Washington.” Canadian Journal of Earth Sciences, v. 42, p. 1389–1400.

Brown, E.H. et al (2007). “Tectonic evolution of the San Juan Islands thrust system, Washington.” The Geological Society of America Field Guide 9.

Carson, Bob and Babcock, Scott (2000). Hiking Guide to Washington Geology. Sandpoint, ID: Keokee Books.

Figge, John (2009). Evolution of the Pacific Northwest. Seattle: Northwest Geological Institute.

Haugerud, R.A. and Tabor, R.W. (2009). “Geologic Map of the North Cascade Range, Washington.”

Joseph, N. L. et al (1989). “Geologic guidebook for Washington and adjacent areas: Washington Division of Geology and Earth Resources Information Circular 86.”

Tabor, Rowland and Haugerud, Ralph (1999). Geology of the North Cascades: A Mountain Mosaic. Seattle: The Mountaineers.

Tucker, Dave (2010): “Baker River limestone and the town of Concrete, Washington.” Northwest Geology Field Trips.

USGS: Geology of North Cascades National Park: Virtual Field Trips.

Washington State Department of Natural Resources: Geology of Washington.

 

Previously published at the Scientific American Guest Blog.