Helenite: can volcanoes really weep gems?

If you are on this blog, you know I’m a nerd. You’re probably a nerd too. Have you ever considered your nerd origin story? Mine began at age 7 or so in the basement of my grandparents’ house in Ottawa, Canada. Behind the washing machine and toy trains, the walls were lined with DECADES of National Geographic Magazines to pore over while the grown-ups wanted me out of their hair. When I was 9 they gave me a subscription so I could amass my very own giant yellow pile of nerdy heaven with priceless pull-out maps. I have an everlasting affection for this magazine. But it’s not the main content of the magazine I want to write about today.

It’s the ads.

In every edition, there’s at least one ad selling the reader some rare, shiny thing – a coin or a gem. The format hasn’t changed since at least 1975. The ad is full of small text raving about the product. There’s a close up with photoshopped sparkles, and a free gift with purchase. This month’s shiny trinket feature seemed tailor-made to my inner magpie. Gems? From a volcano? In my state? How can I be a geologist and never learn about a volcano spitting out gems before!

It, uh, turns out that volcanoes don’t actually spit out gems. More on that in a bit.

First off let me point out some of the positives from this ad, lest I seem too harsh. Helenite is shiny! very green! fairly cheap! 3/3 for Courtney’s inner magpie points. But there is a suspicious amount of purple prose in the ad. Let’s see what a quick google search will reveal.

The ad implies that helenite is a gem linked to the eruption. It weasels out of saying that the gem is naturally created or manufactured, but most people automatically link gems with being natural. The ad also hypes its rarity. Unfortunately they are false on both points.

Mount St. Helens erupted in 1980 in the southwestern corner of Washington, and blanketed the surrounding area in 540 million tons of ash. To give some context, 540 million tons is equivalent to 531.5 USS Nimitz nuclear powered aircraft carriers. Is the raw material rare? You be the judge.

USGS map of ash distribution

The suddenly ashen forest immediately surrounding the mountain was owned and logged by the Weyerhaeuser Company. The helenite legend goes that when Weyerhaeuser went in to salvage their equipment that had been caught in the crossfire, they found a strange effect. Their acetylene torches reacted strangely with the ash as they tried to free their machines. The heat from the torches fused the ash into a novel green glass.

Photo of uncut helenite, from geologyin.com

Of course anything shiny will draw people trying to make a buck, so now helenite is marketed and readily available as a cheap alternative to emerald, or as a souvenir. It’s softness gives it away – it’s only about 5.5 on the Mohr’s hardness scale that ranges from 1 (powdery) to 10 (diamond). An emerald scores 7.5 to 8 on that scale. Manufacturers also add cobalt or gold powder to add a blue or red tint to the finished product, so helenite is sold in a range of colors besides green.

And there have been some studies done that cast doubt on whether helenite is actually made of pure Mount St. Helens ash after all. A 1988 study published in Gems & Gemology melted known Mount St. Helens ash and compared it to a s purchased specimen of helenite. The study found that melted ash from the eruption looked like obsidian – dark gray, not green. The author used x-ray fluorescence and found out that the ash had much more iron and titanium in it which gave the dark gray melted ash its color, and higher quantities of aluminum which made the melted ash melt at a much higher temperature. The genuine Mount St. Helens’ ash melted at 1,300 degrees F, while the helenite melted at 800 degrees F. This variation is much more than you would expect, even given that ash composition within an eruption can vary. I made the dual pie charts from the information in the paper to compare the composition of genuine ash with the composition of green glass…

Even with some canny google searching and combing through the US Patent office, I couldn’t find out who actually manufactures helenite that is sold by jewelers, or how they obtain the ash. Maybe I just have to do an Indiana Jones style Hunt for the Helenite when this COVID-19 thing is over?

All this being said, I would absolutely buy helenite in a gift shop. Especially if it came in teal. After all, my inner 9 year old National Geographic-reading nerd is not that far from the surface.

Shiny!

References:

https://www.usgs.gov/faqs/how-much-ash-was-there-may-18-1980-eruption-mount-st-helens?qt-news_science_products=0#qt-news_science_products

https://geology.com/gemstones/helenite/

http://www.geologyin.com/2016/12/worlds-most-amazing-gemstone-found-in.html

https://www.gia.edu/gems-gemology/summer-1986-green-glass-nassau

https://pubs.usgs.gov/gip/msh/ash.html

https://www.pioneerjewelers.com/blue-radiant-bar-earrings-30h

Rampart Ridge Rocks!

At Vanderbilt University’s Wilderness Skills club we classified adventure into two types of fun. Type 1 fun was fun to experience and fun to remember. Type 2, the slightly more common type, was miserable while it happened but either has a great reward or created a story that got you attention at parties.

The hike up to Rachel Lake after work with a 30-pound pack on my back was decidedly Type 2.

RampartRidgeZoom

Where in the world was I? Trailhead marked in blue, trail in dark green. map created in ArcMap by C. van Stolk using trail shapefiles created by the US Forest Service and ESRI’s Streets basemap.

Rampart Ridge trail map

Trail in bright green – map created in ArcMap by C. van Stolk using trail shapefiles created by the US Forest Service and ESRI’s terrain basemap.

I got off work early on that Friday, headed east on I-90, turned off at the exit for Kachess Lake, bounced up potholed gravel roads to the trailhead, and set out for adventure. I knew the hike went from 2,800 to 4,800 feet in four and a half miles. What I had foolishly overlooked is that it gains 1,400 feet in the last 1.2 miles. A significant distance of that 1.2 miles is literally in a creek bed. It had me questioning my life choices. I had planned to go all the way up to Rampart Lakes at 5,100 feet but I was absolutely done by the time I got to Rachel Lake. I was too cranky to eat my ramen noodles. I set up my tent at the outskirts of an inordinately crowded back country campground just as it got dark, made a cup of tea, and turned in for the night.

The next day was 100% heavenly Type 1 Fun.

I left the burden of my camping stuff where it lay and headed uphill into a clear blue day. My goal was Alta Peak at the northern end of Rampart Ridge, elevation 6,152 feet. I climbed up the ridge past fields of glacier lilies and heather and creeping phlox. It took me about two hours to make it to the top, with views of Mt. Rainier, Mt. Adams, and Glacier Peak. I settled in for an hour with my chair and my map to plan further adventures while I could see so much of the landscape!

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Alta Peak, looking south at Mt. Rainier (center) and the Summit at Snoqualmie ski routes (center right).

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Alta Peak, looking north (the white tip of Glacier Peak is peeking out from behind the Four Brothers on the center right)

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Looking down past the snowdrifts to the basin below Alta Peak

I then rambled downhill to have lunch at Lila Lake. It was hopping with backpackers but I found a nice spot to eat my snack assortment and get yelled at by a marmot.

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Once I had my fill of exploring the bouldery outcrops at Lila Lake, I headed south to Rampart Lakes. I spent the rest of the afternoon basking on a rock with a view at the Rampart Lake furthest along the trail. I braved the water for a swim and dried off in the sun while reading a mystery novel and enjoying my sippy flask of rosé. I did not join the hikers who were penguin-sliding down the snowdrift straight into the lake, though.

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Rampart Lake, looking up at Rampart Ridge.

Around 6pm I headed back down to Rachel Lake to cook dinner and explore the campsite possibilities in the main campground for next time. I went to sleep in an exponentially better mood than I had the previous night.

Sunday morning I hoped to make it down the horribly steep creek bed part of the trail before the day hikers would be heading up it. Mission successful! I took loads of photos of wildflowers. I set up to finish my novel and eat lunch at a rocky waterfall overlook about a mile from the trailhead.

By this point Friday’s uphill slog was completely a thing of the past. All things considered, the trip had been a delight.

But wait! I couldn’t ignore the cool rocks. You know me.

The rocks exposed up at Rampart Ridge were gray with white clusters of larger elongated crystals. I thought they were really distinctive, but didn’t know their name.

It turns out these rocks have the epic moniker of “glomeroporphyritic basalt”. Glomeroporphyritic translates out of science Latin into “collected-together larger crystals”. In geology-ese, “porphyritic” refers to an igneous rock texture where larger crystals are set in a matrix of rock crystals with a much finer texture, like blueberries in a muffin.

Porphyritic igneous rocks form in two stages – the first one at deep in the earth’s crust, and the second in a shallower, cooler zone at or near the earth’s surface. The large white crystals in Rampart Ridge’s basalt formed when the magma was deep underground. They had plenty of time to slowly cool into large crystals in the hot environment at depth. However, some igneous or tectonic process suddenly shoved the magma body up towards the surface. This made the rest of the magma cool suddenly. Because these newer crystals did not have time to grow, they stayed very small.

But why did this one white mineral form crystals at depth, and not the others?  I turn to a familiar chart from my geology textbooks for the answer. It’s called Bowen’s Reaction Series, and describes the order in which minerals crystallize out of molten rock. This series springs from painstaking experiments involving pulverized minerals, a very very hot oven, and more patience than I possess. They revealed that minerals form into crystals at the different temperatures along a gradient.

The elemental mix of magma that becomes basalt creates the white mineral calcium plagioclase and the dark gray/black mineral pyroxene, with only trace amounts of other minerals. Calcium feldspar has a higher melting temperature, and so solidifies at a higher temperature while pyroxene has not yet formed into crystals. An important caveat is that not all magma contains all the elements necessary to make every rock in the series, so several minerals may be “skipped” in a certain magma body.

For example, quartz has the lowest melting temperature of all the common minerals, which is why it often forms decorative crystals or veins in the voids left when other minerals have already crystallized.

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Quartz veins in volcanic rock higher up on Alta Peak.

The two kinds of rock I saw on this hike date mainly from the Eocene and Oligocene time periods between 55.8 and 23 million years ago. Washington was roughly at it’s current location on the globe back then and the volcanoes of the Cascades were starting to rev up. Since then, these rocks have been folded by tectonic forces, broken by faults, and eroded until they cropped out in the patchwork patterns that geologists map today.

rampart ridge edited map

Summarized in MS Paint from the original Snoqualmie Quadrangle Geologic Map by Tabor, Frizzell, Booth, and Waitt of the USGS: https://pubs.usgs.gov/imap/i2538/

The glomeroporphyritic basalt dates from the late Eocene period. It’s colored medium green and marked as Tnbg on the map above.

Tv and the light pink color stands for Oligocene volcanic rocks – an igneous jumble that’s a few million years younger than the glomeroporphyritic basalt. The rocks on Alta Peak are describe in the USGS pamphlet for the Snoqualmie quadrangle as “coarse volcanic breccia and tuff with minor ash flow tuff). They look almost like concrete made with blocky, angular aggregate. Breccia describes rocks created when magma shattered and engulfed surrounding rock as it erupted. Tuff forms when ash becomes cemented by its own heat, like how I described in the Smith Rocks post from 2018. Breccia makes up the ridgeline of the photo below – you can really see how this one rock classification encompasses a bunch of different kinds of rocks that erode differently to create a mix of straight ridge lines and messy talus slopes.

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It’s hard to get a sense of the scale of the waterfall in the center from the photo. I could hear it roaring down the rocks from a quarter mile away!

I’m still doing research about how these rock types ended up juxtaposed. Western Washington’s rocks tell a complex story of bits of foreign continents (called accreted terranes) that were stuck onto the rest of North America by subducting plates, then covered with volcanic rocks and shuffled around by faults. It’s the northern relative to the process in Southern Oregon that I wrote about in my accreted terranes post. Up here, the terranes were even more altered by volcanism and faulting.

It definitely created a fantastic landscape!

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Volcanic breccia on Alta Peak

Resources:

Definition of glomeroporphyritic basalt: https://blogs.agu.org/georneys/2011/07/14/geology-word-of-the-week-g-is-for-glomeroporphyritic/

USGS map and pamphlet for the Snoqualmie Quadrangle: https://pubs.usgs.gov/imap/i2538/

Info on volcanic breccia: https://en.wikipedia.org/wiki/Breccia#Volcanic

Information on Bowen’s reaction series: https://courses.lumenlearning.com/physicalgeology/chapter/3-3-crystallization-of-magma/

 

Ireland: The Giant’s Causeway and Carrick-A-Rede

There are some geologic features that are just way too cool for humans NOT to write a myth about them. The long-standing explanation of the columns of the Giants Causeway was that the giant Finn MacCool wanted to build a bridge to attack his rival in Scotland and that they destroyed the bridge in their fighting, leaving only the Causeway in Ireland and Fingal’s Cave in Scotland remaining. Then that long-standing story gets to rub shoulders with whatever geologic explanation comes along a few centuries later.

On this vacation, we got to road-trip to one of the most stunning geologic sites in Ireland – the Giant’s Causeway.  While we were up there anyways we decided to check out the Carrick-A-Rede rope bridge too, where I got an unexpected extra dose of cool geology.

Ireland trip

Giant’s Causeway is a phenomenal exposure of basalt. Sure, the rock type itself is nothing new. I wrote my thesis about basalt in northeastern Oregon. This particular basalt became famous for the huge field of well-exposed basalt columns, a feature that forms when lava gets the chance to cool slowly. And not only do you get to see the sides of the columns like you can in Oregon, but you can clamber over the tops of them too. It’s well worth the money for the audio tour. There are two versions for two different audiences- normal person and geology nerd – and both are entertaining and informative.

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This basalt flowed out of cracks in the local limestone around 55 to 60 million years ago, when the Atlantic Ocean was opening up. It took two stages to create the landscape here. First, about 6 basalt flows spread evenly across the landscape. Then volcanism stopped for a while; there was enough time for a the top part of the basalt to be weathered a rusty brown color as chemical reaction changed the basalt to laterite, lithomarge and bauxite. This zone is called the Interbasaltic Formation here. There was also time for water to carve a valley into the landscape. Later, volcanism restarted and a huge volume of lava poured into the river valley! At the time of formation, this deposit would have been a lava lake 90 meters (295 feet) deep! We know it had to have happened all in one event, because there are no weathered layers within it.You can see a basalt cliff at the level of my head in the background of the photo to my right – that basalt was deposited on top of the plateau beside the river valley. The thickness of the lava in the river valley meant that it cooled quite slowly, allowing the formation of the regular 4 to 7 sided columns.

You can see what I just described in the photo below. Note that you can see all three layers behind my mom, but that she’s standing on the Giant’s Causeway basalt that flowed into the valley that was cut into the Lower Basalt Group.

Giant's Causeway basalt annotated photo

My mom Lise, always the best tour guide, is here to introduce you to basalt geology! We didn’t hike up to the Organ Pipes, but they’re a beautiful exposure of both the colonnade and entablature layers of the Giant’s Causeway Basalt formation. Finn MacCool’s Chimneys are precarious free-standing basalt columns whose companions were eroded away on the headland.

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Checking out the lower basalt groups – they were physically weathered into rounded shapes as groundwater percolated down into the formation. The fancy name for this is “spheroidal weathering”. You can see a little bit of the Interbasaltic group in the top left corner of the photo, where the dark gray basalt has been chemically weathered into orange/brown minerals.

Whether they’re the ones I studied in Oregon or the Irish ones in this post, basalt flows have a certain internal structure to them. It’s determined by the fact that the molten rock cools mostly from the top down, with a little bit of cooling driven by the cooler ground underneath the flow. The quicker a region of the lava cools, the smaller the size of the cooling features. Air or contact with underlying rock rapidly cooled the lava at the very top or bottom of the flow, giving it a crumbly texture. In the diagram below, these areas are the vesicular top and bottom. Just below the vesicular top, the rock was cooling more slowly. Small cracks propagated from the top of the flow downwards as the rock cooled and shrank. The rock was cooling just quickly enough that the pattern of cracks was somewhat chaotic, creating blocky shapes or the curved and twisting “fanning columns” in this “entablature” zone.

basalt flow interior

Illustration of a basalt flow interior with vesicular zones, entablature, and colonnade from: https://jgs.lyellcollection.org/content/157/4/715

At Giant’s Causeway you can see huge boulders from the entablature zone that have fallen down among the columns. They have kind of a “giant meatball” rubbly texture that contrasts with the smooth elegance of the columns but makes them easy to climb.

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Below that is the sweet spot of cooling, whose features dominate the Giant’s Causeway. In the “colonnade” zone of the basalt flow the cracking pattern propagates neatly downwards. A hexagonal pattern develops when cooling contraction occurs at centers of mass that are evenly spaced in a homogeneous body of lava. If there are variations in the thickness or composition of the lava then other geometries of fracture may occur, with anywhere from 4 to 8 sides.

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Giant’s Causeway’s famous colonnade layer, with geologist for scale.

You can see in the picture above that the columns are broken by joints perpendicular to the ones that define the columns. These are subtle ball-and-socket joints that formed when the area was subjected to horizontal stresses after the rock had cooled and the columns had formed. These ball-and-sockets allow the formation to bend a bit.

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concave “socket” column top on the left, convex “ball” column top on the upper right.

Later that day the sun came out and we decided to check out the Carrick-A-Rede rope bridge. It’s absolutely touristy but worth it on a beautiful day like that. The bridge and island are only accessible by paying for a group tour that departs at regular intervals. You end up parking in a nearby abandoned limestone quarry called Larrybane Quarry.  It has beautiful seaside views, and a fight scene from Game of Thrones was filmed here.

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Unfenced drops? Cliff edges? Count me in. Spoiler alert, our mom did not keep us close…

How can you ask a geologist to stay on the path when there are cool chert nodules to investigate in sea caves? In the right-hand photo, the black rock is chert. In the photo with my sister and me in it on the left, you can see how these chert nodules are distributed in horizontal bands in the limestone. These nodules are formed after the remains of microscopic organisms like coccolithophores, radiolarians, and diatoms are laid down and start to solidify into rock. Water in the formation dissolves some of the silica-rich remains and redeposits them in layers around impurities in the sediment, forming blobs of chert that are often called “flint” when they’re found in chalk beds like these.

In the top right corner of the photo you can see stalactites – this is the only known location in the Ulster Limestone (a.k.a. Upper Cretaceous Limestone) along the Causeway Coast with these distinctive formations.

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When the line of tourists waiting to get across the bridge is longer than the bridge, it might be a tourist trap.

This was just a detour to the main attraction – the Carrick-A-Rede rope bridge. It was constructed in 1755 to allow fishermen access to fruitful salmon fishing groups, and has been developed as a somewhat oversold tourist attraction. It has a neat geologic history though. The little island stands tall because it’s the eroded neck of a volcano! It formed 62 million years ago, just a little bit before the basalt at the Giant’s Causeway. The island is formed of dolerite, a kind of intrusive volcanic rock. When you’re on the island and looking back to the mainland, you can see large blocks of basalt and limestone suspended in a matrix of volcanic ash.

 

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The short hike to the bridge takes you down rocky staircase and along gravel paths with lovely views out to sea. The tour guides don’t encourage the group to spend too much time on the island itself, but we got to take twenty minutes or so to spy on the seagull nests, eat some snacks, and admire the view out to Rathlin Island.

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Here’s a map of an overview of the geology around Giant’s Causeway and Carrick-a-Rede that I put together in ArcMap. This is from the 1:500,000km shapefile available from the Geological Survey of Ireland. The more detailed 1:100,00K map excludes Northern Ireland… I guess political animosity somehow spilled over into data collection and sharing here. That’s a shame. So Carrick-A-Rede itself isn’t mapped here.

Northern Ireland Geology

Stay tuned for a geology/archaeology crossover event! My family headed to the Newgrange Stone Age Passage Tomb later that week.

Resources:

https://www.geolsoc.org.uk/GeositesGiantsCauseway

booklet on the geology of Northern Ireland’s Coast: http://ccght.org/wp-content/uploads/2012/05/geology_booklet.pdf

A field trip at the Sand Atlas blog whose author took some better photos of the formations: https://www.sandatlas.org/giants-causeway/

Debbie Hanneman over at GeoPostings did this trip back in 2017 and shared some great photos: https://www.geopostings.com/category/giants-causeway/

AGU resource on columnar jointing: https://blogs.agu.org/georneys/2012/11/18/geology-word-of-the-week-c-is-for-columnar-jointing/

Information about the geology at Carrick-A-Rede: http://www.habitas.org.uk/escr/site.asp?item=1145

Article about the formation of chert nodules in carbonate beds:

Maliva, Robert G., and Raymond Siever. “Nodular Chert Formation in Carbonate Rocks.” The Journal of Geology, vol. 97, no. 4, 1989, pp. 421–433. JSTOR, http://www.jstor.org/stable/30078348. Accessed 14 May 2020.

Cool podcast about the tiny creatures that become chalk, courtesy of Radiolab: https://www.wnycstudios.org/podcasts/radiolab/articles/190284-war-we-need

Why can Mont Saint-Michel withstand the tides?

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I’m on the left, Heather’s on the right, with Mont Saint-Michel!

It’s hard to miss the stunning abbey/fortress of Mont Saint-Michel as you drive along the coast towards it. It stands proudly above the surrounding flat estuary with flocks of particular salt-tolerant sheep grazing on the marshes.  The abbey and town grew to cover almost all of the original rock exposed on the Mont – they’re built out of rock from the Mont itself and from nearby islands in the English Channel. It seems incongruous and bold beyond belief that someone would built it so far out onto the marshes and the tidal plain, far from dry solid land. So why were the abbey and fortress built here? What allows them to stand the test of time and tides? It turns out, it’s the geology. Look for Mont Saint-Michel on the map below (hint = look for the red dots)…

Mont St Michel surface geology IMS 2017

Surface geological map of the area around Mont Saint-Michel, taken from the proceedings of a 2017 field trip of the International Meeting of Sedimentology prepared by Bernadette Tessier and Pierre Weill

It was built on an outcrop of hard granite that stands tall as the tides shift the soft sand and silt around it.

Beneath the veneer of Quaternary sediment from the estuary, the region is made up of mudstones and sandstones that were transformed into metamorphic rocks between 600 and 570 million years ago at the root of an ancient mountain chain formed by an oceanic crust – continental crust subduction zone. At that time, this chunk of northwestern France was connected to the ancient continent Gondwana, and located near the south pole. Around 525 million years ago, magma rose off of the subducting oceanic plate and pushed up through the cooler, denser metamorphic rocks. This magma cooled to form the igneous intrusions that would become Mont Saint-Michel and the nearby Mont Dol and Tombelaine. These instrusions were made of a unique rock named leucogranite, notable for the lack of dark felsic minerals such as amphibole or pyroxene. Pink feldspar, grey quartz, and clear quartz give Mont Saint-Michel’s rocks a beautiful pale color.

Intrusive igneous rocks such as the leucogranite at Mont Saint-Michel are much more resistant to erosion than the shales, schists, and sandstones that they intruded into. Over time, this difference formed hills, cliffs, and outcrops along the coast of Brittany. This is evident in a cross section of the Bay of Mont Saint-Michel compiled by France’s geological survey below:

BRGM Mont Saint-Michel Cross Section

Translation – “Geologic Cross Section across the bay, passing by Mont-Saint-Michel and Tombelaine”. “schistes tachetés” = speckled schist, “digue des polders” = polder seawalls

It turns out that these rocks have been on a long, strange journey.  This part of Brittany and Normandy belongs to a tectonic fragment defined by its experience as part of the Avalonian-Cadomian belt  around 600-500 million years ago close to the South Pole. These rocks – schists, sandstones, and intrusive volcanics – were formed at the roots of a mountain chain at the northern edge of Gondwana , as oceanic crust subducted beneath regions of Gondwana that now form northern Africa.  You can see a reconstruction of its historical place on Gondwana in the inset map of the figure below, and the main figure shows the modern position of that block in northwest France and underneath the English Channel.

Cadomian Block Map Chantraine et al 2001

This figure shows the Cadomian terrane shortly after it began to split, around 490 years ago. Image from The Formation of Pangaea by G.M. Stampfli et al, 2013, via https://quatrevingtans.net/2014/04/

Baltica, Laurentia, and the Avalonion Terrane shown on the map above later collided to form the continent Laurussia during the Caledonian Orogeny around 410 million years ago… with our featured Camodian block steadily heading northward but not quite there yet. On the figure below, it’s part of the lump labeled “Armorica??”

formation of Laurussia caledonian orogeny

By Woudloper – Own work, CC BY-SA 1.0, https://commons.wikimedia.org/w/index.php?curid=5038110

This piece of the Cadomian terrane didn’t get sutured onto the rest of France until about 320 million years ago – it had rifted off of Gondwana and ran into Laurussia as part of the Variscan Orogeny that finished the formation of Pangaea. The aftermath of the Variscan orogeny is shown in the figure below, with our featured location indicated by the teal dot.

variscan orogeny MSM note

Close up of the collisions between Gondwana and Larussia, with Baie de Motn St Michel as a teal dot. Current continental outlines are approximated with grey lines. Picture By Woudloper – Own work, CC BY-SA 1.0, https://commons.wikimedia.org/w/index.php?curid=5330107, edited by the author

Since then this fragment of the Cadomian terrane has hung on tight to the rest of France as Pangaea ripped apart and the continents shuffled around to their modern configurations. Through these 600 million years Mont Saint-Michel’s geologic setting moved from the south pole to around 45 degrees north, switched continents while remaining intact, survived the breakup of Pangaea and the opening of the Atlantic ocean, and eroded to its modern form.

This area doesn’t preserve any of the geologic record from the Paleozoic or Mesozoic eras, and the only record of the Cenozoic era are certain Oligocene marine sediments in the bay. However, its Quaternary sediments since the last glacial maximum give scientists plenty to study, and account for much of its dynamic recent history. At the height of the last ice age around 15,000 years ago, wind-blown loess and sand covered much of the ancient geologic platform.This is shown in the map below – you may have to click on it for the full version in order to read the text. I added English translations in blue text.

BRGM baie de MSM 10000 ya traduitAround 8,000 years ago the sea level rose to intrude into the bay, creating the topography that we see today. The defining sediment around the Mont Saint-Michel nowadays is “tangue” – a salty fine-grained mix of clay, silt, and shells. It’s created by the competing forces of the three rivers discharging sediment into the bay and the force of the tides which rework that sediment and add the pulverized shells. Elsewhere in the bay, the dominant sediment is bioclastic sand, which is a fancy way of saying sand made up of bits of shells.

The Baie de Mont Saint-Michel has the 5th largest tidal range on earth thanks to its position at the mouth of the English Channel – 14 meters! This huge tide, in combination with the sediment flowing out of the rivers See, Couesnon, and Selune, adds 400,000 to 700,000 cubic meters of marine and terrestrial sediment to the bay each year. This natural influx has slowly filled in the tidal area that isolated the Mont, but human actions have accelerated this process. In the 1850s, polders and dikes were built to extend the arable and pastoral land around the three rivers in the estuary. This ate up area on the tidal flats. Additionally, a dam was built on the Couesnon River in 1969 that eliminated its ability to flush sediment out of its mouth in the bay. To add insult to injury, a permanent parking lot was built up above the tide adjacent to the Mont to allow visitors easy access. It seemed imminent that Mont Saint-Michel would become a part of the mainland, a peninsula when it was once an island.

In 2006, work began on projects to preserve the maritime character of Mont Saint-Michel. This included relocation of the parking lot from adjacent to the Mont to further inland, constructing an elevated causeway that allowed water and sediment to flow underneath it, dredging the channels of the Couesnon and adding riprap structures to split the flow of the Couesnon in two near the Mont, modifying the dam on the Couesnon so it could allow the river to flush sediment more powerfully at the receding tide, and restoring marshes on the Couesnon to trap sediment upstream. The goal of all this was to deepen the water directly around Mont Saint-Michel by increasing the erosive power of the Couesnon River and removing obstacles that collect sediment.

The following map shows the difference in elevation around the Mont, measured by LIDAR, between February 2009 and September 2019. The project has been quite successful so far!

 

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  • The erosive fringe to the right of the eastern grassy area is still present but stable in the absence of an active channel in the zone.
  • The zones of erosion directly to the north of the Mont have increased (140m in width and 1.80m in thickness in places)
  • The zone of erosion to the right of the western grassy area has grown (150m in width and 2.5 m in height), with a significant reactivation of the western stream..
  • Erosion through the large western bank was increased and the area was enlarged.
  • The western and eastern channels rejoin to the south of the Mont, creating strong erosive forces in the zone, -4m in places.
  • Zone of enlargement of the large western bank to the north of the Mont still present and growing (until +2.5m).

All of this does not reverse the sediment deposition in the bay – there’s no way for us to permanently fight the influx from the incoming tide and the three rivers in the bay. However, it does reverse the human-caused processes that were accelerating the accumulation of sediment around Mont Saint-Michel.

And just from a touristy viewpoint, I enjoyed the pedestrian bridge and the removal of the parking lot and visitors center from directly in front of the historical site. It makes me feel more like I’m approaching a medieval fortress and less like I’m approaching a historical theme park. The new parking lots and visitors center are surrounded by marshes and trees, and the short walk to the Mont is beautiful.

This UNESCO world heritage site was more than worth the drive just for the history and the fun of exploration, and seeing its unique place in the landscape was also fascinating! I was thrilled to check this place off my bucket list!

Resources:

Extremely thorough French-language geologic and sedimentologic paper and maps of Baie de Mont Saint-Michel by France’s geological survey: http://ficheinfoterre.brgm.fr/Notices/0208N.pdf

Great, detailed English-language resource of the geology and sedimentology of the bay: https://www.unicaen.fr/m2c/IMG/pdf/field_trip_mtstmichel_bay_ims2017_toulouse.pdf?916/99338f5f109256e86ac5bb88aa170b32c7a5714e

Chantraine, Jean, et al. “The Cadomian active margin (North Amorican Massif, France): a segment of the North Atlantic Panafrican Belt.” Tectonophysics, vol. 331, 8 Oct. 1999, pp. 1-18.

Stampfli, Gérard & Borel, G.D.. (2002). A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored synthetic oceanic isochrons. Earth and Planetary Science Letters. 196. 17-33. 10.1016/S0012-821X(01)00588-X.

Excellent summary of the history, sedimentology, and restoration of the bay: https://throughthesandglass.typepad.com/through_the_sandglass/2009/09/montsaintmichel-a-massive-sedimentology-experiment.html

French-language field trip guide to the bay: https://sgmb.univ-rennes1.fr/vie-associative/excursions/12-excursions/47-baie-du-mont

French-language resource on the project to restore the bay: http://www.projetmontsaintmichel.fr/index.html

Strike, Dip, and Skis

Hoodoo summit

Mt. Washington selfie on top of Hoodoo Butte!

It’s been something of a theme in my recent blog posts that the west-coast mountains are a source of nerdy joy for this recently transplanted geoscientist. This winter I went on my department’s grad student ski weekend to try out this whole zooming-down-mountains-on-sticks thing and get a chance to hang out at Mt. Bachelor with a convivial bunch of folks. I got thoroughly hooked despite spending much of my time crashing on the bunny hill and watching the 4-year-olds effortlessly ski past me. It’s a whole new way to appreciate the volcanic history of the northwest! (hmm, that sounds like a blog post series once this term is finished…)

Two weekends ago I progressed to wiping out on the blue-level slopes instead of the greens (baby steps!), and a thought hit me out of the blue that dramatically improved my control over my skiing.

‘What would a Brunton compass tell me about this line?”

I promise I hadn’t hit my head and lost my marbles on the previous “yard sale” fall where my scarf, poles, and skis ended up strewn around me. For my non-geologist readers, a Brunton compass is the strange but useful combination of a compass, mirror, and level that geologists use to measure the dip (steepest angle) of a tilted piece of rock as well as the strike (cardinal direction perpendicular to dip, and the direction where the Brunton is completely level).

I was skiing down the Glade route at Timberline and my trusty “aim to the edge of the run to slow down” method was failing me miserably half of the time. I had a flashback to the last time I was in mountains, swearing at my Brunton at Indiana University’s field camp in the mountains of Montana. In that moment of clarity I realized that if the mountainside was a tilted rock layer I was expecting the route to be perpendicular to the strike (true dip, i.e. straight down) while it was actually at an angle (following a shallower apparent dip). By aiming to the edge I was going to the steeper true dip and accelerating – exactly the opposite of what I wanted to to do!

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It’s a universal truth in physics, particularly noticeable for people who ski or mountain bike, that the steeper your trajectory the faster you’ll accelerate. Friction determines the maximum speed. In my case gravity conspires with my properly waxed skis to set my maximum speed on the steeper blue routes much faster than I have the skill to control, hence the wipe-outs.

If the route is straight downhill following the “true dip” of the geologic example, I can ski either to the right or left to decelerate to a more comfortable speed. This holds true for the “Over Easy” route I first skied/slid down at Mt. Bachelor, most routes at Mt. Hoodoo, or for the Magic Mile routes at Timberline. These routes are aimed pretty much straight down the side of the mountain.

true dip skiier

However if the route is at an angle to the steepest possible line, then it is following the geologic “apparent dip” of the landscape. In that case, if I ski to my right, away from the angle of the route, I would find myself skiing at a steeper angle towards the true dip and accelerating into a snow bank.

apparent dip skiier

Geology students find ourselves tripped up in less spectacular ways when faced with eroded inclined structures, where the true dip of the rock bed isn’t perpendicular to the eroded top of the formation.

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Week 5 of field camp: why the heck is the hillside shaped like an “M”?

On a contorted landscape like these hills near Doherty Mountain in Montana, it was all too easy to ignore the wobbling level bubble in my Brunton compass in the rush to finish surveying an area. After the first day we all put our notes together and realized that none of us agreed on the dip of the hillside. We had been fooled into interpreting the easiest path to walk across the hill as “horizontal” and measured various apparent dips.

apparent dip geologist

As enjoyable as my class made it to trek up those hills through the bushes and snakes, wouldn’t it be even more fun to ski  down them over a nice smooth blanket of snow…

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Road Trip Part 4: Columbia River Gorge

This is the final installment of my series following my father and my cross-country road trip from Tennessee to Oregon so I could start my master’s program at Oregon State University.

Road Trip Part 1: Why are the high plains so flat?!

Road Trip Part 2: Wyoming’s Great Divide Basin

Road Trip Part 3: The Wasatch Range

Day 6: Salt Lake City, through Idaho, to Pendleton, OR. Sorry Idaho, I’m skipping your geology, maybe another blog post…

Day 7: Pendleton, OR to Corvallis, OR!

The last big geologic conundrum of my trip was the giant layer cake of volcanic deposits that came into view along Highway 84 just past Boardman. The Columbia River sliced through it like a knife, revealing stair-stepping steep cliffs.

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Highway 84 clings to the side of these cliffs for dear life, and every now and then a spur road would snake up the cliff to a town perched high above.

Welcome to the Columbia River Gorge! The river has cut 4,000 feet down into almost  basalt deposits up to 2 miles deep over the past 15 millions years, and the results are amazing.

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Tennessee’s only volcanic rocks are thin ash deposits, so this landscape was utterly foreign. My research on the topic was delayed by the first three blog posts and a 20-page paper on the philosophy of geography, but during the week of final exams I found Central Washington University professor Nick Zenter’s engaging video series on YouTube.  He gives a wonderful introduction to the geologic world of the Pacific Northwest in a format that’s friendly to both non-geologists and geologists whose brains are too fried by studying to read off-topic academic journals. Manatash Mapping out of Ellensburg, WA made some of the best maps I found of the basalt flows to accompany his lectures: the one below shows the total extent of the Columbia River basalts! The Columbia Gorge is not indicated on these maps, but it defines the OR/WA border from just south of Pasco, WA to the Pacific Ocean.

Zentner_CBG_ExtentMapC

Brown shading = the sum of the area covered by over 300 basalt flows. 63,320 square miles in all!

This giant pile of 41,985 cubic miles of basalt was belched out by a swarm of “dikes”, or vertical ruptures in the Earth’s crust where lava escaped, between 17 million and 6 millions years ago. 80% of this lava came to the surface between 16.5 and 15.5 million years ago as part of the Grande Ronde Member, which we saw as we drove through the Columbia River Gorge. The Grande Ronde basalts flowed out of the dikes in the area where Washington, Oregon, and Idaho’s borders meet on the map below.

MapEFinal_WithAllDikes_20161012

Orange = area covered by Columbia River Basalt Groups, Black lines = approximate locations of dikes

The next map shows the approximate depths of these lava flows, focusing on the Washington-Oregon border. While depths in the Gorge are between 0.5 and 2 miles, the flows are 3 miles thick in south-central Washington!

Zentner_Pa_Isopach

These flows continued east, following the path of the Columbia all the way to the Pacific. However west of the Cascades, as we approached Portland, the wetter climate hides the sheer cliffs with a carpet of trees.

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Looking upriver from an overlook near Hood River, Oregon.

But what caused the Earth’s surface to split open and spew out vast sheets of lava? 16 million years ago in the middle of the Miocene period of geologic time, northern Oregon and southeastern Washington would have looked a lot like the fiery slopes of Mt. Kilauea in Hawaii, or Mt. Bardarbunga in Iceland.

Bardabunga-volcano

Pendleton, OR in the Mid-Miocene?

Geologists don’t have a definitive answer yet, although many interacting geologic events have been proposed to have contributed to the eruptions.

  1. The eruptions may be related to the historical path of the Yellowstone Mantle Plume, or “hot spot”. The oldest dikes in southern Oregon opened up just as the Yellowstone hot spot was erupting in what is now northern Nevada, directly south of the dikes.
  2. As the North American plate moved to the southwest over the hot spot towards its current position, cracks in the crust radiated northward, likely along lines of weakness between accreted terranes (bands of islands and sea floor scraped onto the continent by subducting plates) and the core of the continental shield.
  3. As the Farallon oceanic plate collided with and sank beneath the North American plate, crumpling the Coast Ranges and creating the stratovolcanoes of the Cascade range, these stresses could have helped open up these dikes. The majority of the dikes are perpendicular to that west-to-east direction of stress, which would be typical, and the eruptions happened directly after the collision.
  4. It’s possible that after the Farallon Plate slid under North America, parts of it tore open along long north-to-south trending lines. A tear in this subducted plate could allow hot rock to rise up from the upper mantle and punch through weaknesses in the crust.

Luckily for us these dikes have been quiet for the past 6 million years, and don’t show signs of starting back up. Nowadays, only water flows through the Columbia River Gorge. I’m looking forward to going back and exploring the many waterfalls that feed into it this spring as during our road trip in late August 2017 the area was ablaze for a different reason –  forest fires!

References:

Columbia River Flood Basalts | Volcano World | Oregon State University. (n.d.). Retrieved December 7, 2017, from http://volcano.oregonstate.edu/columbia-river-flood-basalts
Liu, L., & Stegman, D. R. (2012). Origin of Columbia River flood basalt controlled by propagating rupture of the Farallon slab. Nature, 482(7385), 386–389. https://doi.org/10.1038/nature10749
Zentner, Nick, Narrator. Flood Basalts of the Pacific Northwest. , Central Washington University, 2017, https://www.youtube.com/watch?v=VQhjkemEyUo&t=2967s. Accessed 15 Jan. 2018.

Applying to graduate school with Courtney and Beaker

 

If personal narratives aren’t your cup of tea I totally understand if you want to skip this post and wait til I post something involving rocks (Road trip part 4 is coming soon, I promise!). I’m writing this post for those who stand where I stood in May 2013, struggling to define their academic goals and career path.

Tl:dr version: You aren’t alone if you don’t have any idea of what you want to do for grad school or careers straight out of undergrad. Take the scenic route, try out jobs, and ask a lot of questions!  And just like in any scientific endeavor if you fail, take a good hard look at your methods, gather a team, and try again.

If I hear someone say “You can do anything!” one more time, I will probably have an allergic reaction that causes me to sprint out the door and down the street while making small panicked noises like Beaker in the Muppets.beaker_meep__meep__meep__animated_badge_by_blue_staple_studios-d94gpzx

(possibly my spirit animal)

‘Tis the season for graduate school applications, so I thought I’d share how I ended up at Oregon State! It meant taking some relatively risky moves instead of the safer option of staying in one place, as if my true calling would one day show up on my doorstep if I was patient enough. This was nerve-wracking but rewarding and involved doing things like decamping to California for a seasonal job, or prying myself out of my introvert shell to cold-email dozens of people. Early in the process of thinking about graduate school, when I heard a well-meaning “you can do anything you want!” some part of my brain translated it it to “you should do everything, if you aren’t then you’re failing, and what if you miss an opportunity of a lifetime while you’re doing something else?”

Because of that fear of commitment, graduate school application was initially an intimidating process for me in my senior year of university. Grad schools require a different mindset than undergraduate programs to apply because the academic and personal fit between the applicant and advisor is so crucial. There’s no Princeton Review guidebook to give a tidy 1-100 ranking of schools. I didn’t even know how to formulate the questions to get help choosing a program then. I would have needed my advisor to dive inside my head and read my mind, which is still firmly in the realm of sci-fi. Talking to grad students at Vanderbilt, they made it seem so effortless to make up their minds about what subject they wanted to devote 2-6 years to. It flowed out of an undergraduate research project, or a natural interest, or something that “just made sense”.

It didn’t help that, by the fall of my senior year, the interdisciplinary major that I had designed to study climate change was revealing to me exactly how complicated that issue was and how it could weave itself through any narrative I looked at. Did I want to study paleoclimates, or atmospheric sciences, or environmental justice, or energy sustainability, or…..? Indecision froze me like a deer in the headlights.

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Beaker trying to disappear

Several different possible paths occurred to me that spring of my senior year. I could go into private or public research, which would eventually require a higher degree and those mystifying applications to graduate school. I could look into becoming a park ranger, guide, or outdoor educator, based on both my academic and non-academic passions. I could go into the nebulous field of “consulting”, based on a conversation at an environmental careers dinner. So, I figured that it would be best to try them out.

To start off with I got a fantastic GeoCorps internship at Mammoth Caves National Parks, where I learned that being a park ranger involves unlimited outdoor time frolicking through natural science (and facilities maintenance), but also finding a new posting every six months and a best-case scenario of being promoted to a stable management job where I would be banished to an office.

Who needs free weights when I have a hammer drill and a 6-mile hike to the cave entrance?

With a bit of legwork I got a position as an intern at an environmental consulting firm where I learned the nuts and bolts of regulations and customer service, and how complicated it is to balance clients’ business interests and the environment.

C with tanks.jpg

After the terms of that internship came to a close I headed out to California to work for Naturalists at Large, where I learned that no matter how much I can geek out over geology, rock climbing, and birds, keeping classes of middle school students amused is not my forte, and neither is finding a new outdoor recreation gig every single season.

This process of elimination left grad school, probably earth science as a career, and my nature cravings as a side hobby.

While in California I had applied to Indiana University’s summer field school (and only that one field camp, because I still felt like relying on dumb luck), because I figured that if I were to go the grad school route I would need it. In a ringing endorsement for dumb luck I got in, and it changed my life. No, seriously. I was doing science! I didn’t have to worry about whether I was cut out to be an earth scientist, because I was doing the earth scientist things, and doing them well! Hiking around the Tobacco Root Mountains of Montana wasn’t half bad either.

Stream temperature experiment/pool party at the Firehole River in Yellowstone National Park

In hindsight, field camp bumped me up to about 40% ready to apply to graduate school from 10%.

The next 20% was acquired over months of job applications, paper-reading, blog-writing, talking informally with professors and professionals, tutoring middle- and high- school students in earth science and English literature, volunteering with a USGS data analysis project, and getting hired full-time at the environmental consulting firm where I had interned. I went to visit professors at University of Pennsylvania, University of Delaware, and Johns Hopkins while living on my sister’s couch for a few weeks, which gave me practice talking with professors, a sense of how graduate programs were structured, and desensitized my anxious self to interviews. Volunteering as a data analyst with the USGS gave me an additional recommendation-letter-writer as well as experience with data analysis! Through all that, I narrowed down my impossibly wide interest to water issues stemming from climate change, leaning towards quantity instead of quality.

The last 40% was gained in four months of targeted cold-emailing of potential advisors, phone calls with those professors, obsessive research in my field, and a 2015 Geological Society of America conference where I walked up to random people and piped up “Hi, my name is Courtney, I’m currently working in environmental consulting, what do you do?” followed by a few minutes of listening, followed by “where should I go to graduate school to study how climate change and human use patterns affect water resources?”. You’d be surprise how well that works. It’s shockingly easy. If you had told me in my senior year of college that I would do that 15-20 times in a day I would have backed away quietly with a polite and petrified grin plastered across my face. Geologists being a friendly bunch, sometimes people told me “ask that guy over there, I’ve got no clue”, and most were happy to give me a lead or two.

I explored civil engineering, hydrology, geology, and geography masters programs. Because of my interdisciplinary interest, I ended up focusing on large state schools that had the breadth of faculty and funding to have created a dedicated working group for water resources. I had enjoyed creating my own major in college, but wanted the stability of an existing program to give my Masters degree more weight and to not have to explain it in detail to everyone I meet. Geography programs really stood out here – Vanderbilt didn’t have a department in this field, but I realized that it was pretty much perfect for me!

Based on all of these conversations at GSA and elsewhere, I figured out what angle I wanted to take on “water issues stemming from climate change, leaning towards quantity instead of quality” – geographical methods, instead of strictly hydrological or ecological.

Then I made a spreadsheet based on that info, and set about fleshing it out.

grad school spreadsheet screenshot.png

It has 34 rows, one for each potential advisor I contacted at twelve schools.

This might give the impression that I’m a naturally organized person who loves cold-calling, which isn’t the case. It’s challenging for me and sometimes prompts me to curl up in a blanket at 5:30 in the evening with soothing instrumental folk music. However, it’s the hurdle to get to science that I love and opportunities that I need, so I made myself the tools to get over it. I set a goal of four professors or current grad students contacted per week, and met it most weeks. I found out that no matter how many intelligent questions I think of before I call a professor, they will all fly out of my head once I’m on the phone unless they’re written on a sheet of paper in front of me, preferably in several eye-catching colors of pen. I have a wonderful sister who will reassure me that I’m a worthwhile person when I text her at midnight after hours of tying my thoughts in knots about an awkward conversation. Spreadsheets help me fish thoughts and information out of my brain, put them in words, and manipulate them in a useful way.

For example, University of Arizona took about 10 hours of research, 3 calls to current grad students, 3 calls to faculty, and a spreadsheet of its own to sort out the tangle of water research options and who teaches where.

u of a spreadsheet screenshot.png

Based on all that information, I narrowed my choices down to geography programs at five universities. That done, I had to make it easy enough for myself to keep track of the five applications that I would actually complete them and not forget anything. This meant another spreadsheet… and a whole lot of refreshing my email inbox.

apps spreadsheet screenshot.png

And after all this work, I got into exactly 0 schools in the spring of 2016. For reasons related to over-committed professors, funding cuts, and the fact the I applied to the most competitive programs in my field, I wasn’t judged to be a suitable enough fit to accept and fund. April was a pretty ghastly month for my mental state as I frantically tried to piece together another timeline for my life that didn’t involved driving off into the sunset towards a graduate program in August 2016.

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Beaker’s file being tossed…

I allowed myself about two solid weeks of denial, self-pity, and comfort food, and then I reached out to some lovely friends who shut down the pity-party. We made a list of next steps:

  • Reach out to the schools to request a post-mortem of my application
  • Take the ASBOG exam to work towards professional development and freshen up my geology skills
  • Continue with my current job
  • Take a statistics course
  • Write appealingly nerdy things on my blog
  • Get a gym membership and start climbing again with my newfound free time
  • Restart the grad school search in August 2016, and try to focus it more on research
  • The silver lining: I now had an extra year to make myself that much of a better candidate.

In the fall of 2016 I reapplied to Oregon State and applied to San Diego State, University of Waterloo, and Southern Illinois University using the same tools and all that knowledge I had gleaned from potential professors/advisors in 2015. I had described a broader focus on my 2015 applications, but had focused my interested down to the geography of groundwater management during the 2016 applications. This 2016 specialization allowed me to better pinpoint potential advisors and make the case for how I could fit into their programs, and also probably made me look like a more committed candidate on my applications. I figured that if I had gotten into 0/5 schools in 2016, I might get into 1 out of 4 schools in 2017.

What did I do differently?

  • Reached out to professors earlier in the fall
  • Had a more defined research interest
  • Asked more specifically if they had research they could fund me for, or if not who in their department did
  • Posted on the Earth Science Women’s Network Facebook page asking for recommendations of schools with ambitious and possibly underrated groundwater faculty that weren’t on my radar
  • Stayed in closer contact with my letter-of-recommendation writers

In the spring of 2017 I won the grad school applicant lottery – I got into all! Four! Schools! All the important people in my life had to deal with text messages IN ALL CAPS ALL THE TIME HOLY MOLY.

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Beaker playing “Ode to Joy”!

I hope that the takeaway of all this is that if you’re applying to graduate school, you need to talk to people. As many people as possible. This was my biggest obstacle when I first started applying – I didn’t want to bother anybody. Additionally, I was ashamed to ask for help even when I knew how to articulate my questions, as I thought it would make people think I wasn’t good enough to begin with. Eventually I learned that few people are bothered as long as I did research beforehand to avoid asking them to regurgitate the contents of the personal website for my benefit, which nobody has any inclination to do.

I found that academics, students, and professionals alike generally like talking about what they do and helping people out if they’ve got the time. An applicant can take respectful advantage of that to learn what’s out there. The worst anybody can say to you is “no”, and it’s almost never personal. It boils down to seeing if the professor is doing what you want to study and has funding, and then convincing them that they really do need your unique talents and brainpower.

And don’t worry if those talents change from conversation to conversation, especially if you have an insanely broad initial focus like I did. I settled on a messy process of deciding on a certain way of selling my skill set to a potential advisor so they would at least talk to me, using what I learned from that conversation to improve my focus, and then pitching that improved focus again or to another professor. Sometimes I talk about different research ideas with different potential advisers, just to see which one I enjoyed talking about the most. I had barely managed to pull together a coherent idea of a academic goal as I careened into the December 2015/January 2016 deadlines, and came up with the new and improved version 2.0 by December 2016.

If I have to pick a metaphor for finding my calling after college, it’s less like a package delivered to my doorstep and more like a Pony Express run to deliver a shapeshifting package to an address I can only find at the end of a scavenger hunt. But I made it, and you can too.

Happy trails!

If you want to pick my brain, to commiserate, a copy of my spreadsheets to use as a template, or advice for cold-emailing, let me know in the comments.

Road Trip Part 3: The Wasatch Range

Road Trip Part 1

Road Trip Part 2

Days 4 and 5: Salt Lake City, Utah

Of all the places for my car to start hemorrhaging power steering fluid, Salt Lake City turned out to be one of the better ones.  I dropped it off at the mechanic and then my cousin Scott distracted me with a trip up Little Cottonwood Canyon to one of his all-time favorite places – the Snowbird ski resort.

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View from the top of Hidden Valley Peak!

Scott said he always enjoyed introducing out-of-staters to his hometown, but I hope that my constant stream of “oh my GOSH WOW” coming from the backseat on the way up the canyon didn’t get too annoying.  I mean, what’s a geologist to do? We passed glacial moraines AND fault scarps AND giant granite intrusions AND hanging glacial valleys AND massive thrust-faulted hodgepodges of sedimentary rock AND not to mention that view of Salt Lake to the west…

All this is possible because Salt Lake City and the adjacent Wasatch Range are perched on a unique boundary – the very eastern edge of the Basin and Range Province of the USA. Yep, you guessed it, it involves the Laramide Orogeny like everything covered in my last two posts, but also the Laramide’s fraternal twin mountain-building event. Meet the Sevier Orogeny.

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(courtesy of the Wyoming State Geological Survey)

Both the Sevier and the Laramide  happened at roughly the same time (70-50 million years ago) on account of the same pressure (the subducting Farallon Plate). However, two areas of the USA responded differently to the pressure. In areas further east, such as Colorado, eastern Wyoming, and Montana, that pressure hit areas of the continental basement which had been weakened when the supercontinent Rodinia was ripped apart 750 million years ago (mya) and the Ancestral Rockies rose around 300 mya. The weakened continental basement rock buckled under the stress. Geologists refer to this as “Laramide-Style” orogeny, and I saw its results in the Colorado Rockies and the “basement-cored” ranges in the South Wyoming such as the Rawlins and Rock Springs uplifts.

The pressure from the colliding and subducting plate manifested differently further west (Utah, Western Wyoming and Montana) where the continental basement rocks had not been cracked by previous mountain-building or continental rifting. Here, the many layers of sedimentary rock deposited in the Cretaceous Seaway took the strain as the basement rocks got scrunched together. These thin layers cracked and thrust over each other like shuffled decks of cards, creating the thin-skinned “Sevier-Style” orogeny. This style is evident in jumbled, repeated bands of rock in the Wasatch range. The corresponding geologic map looks like one of those scribble-and-fill masterpieces that happened when I first discover MS Paint in 6th grade.

Snowbird geo

Geologic units on the Snowbird property (blue boundary) – note the repeated purple, lilac, and mauve bands of rock. These represent sedimentary units between 1 billion and 350 million years old! The yellow blobs on top are bulldozed bits of sediment from glacial activity ~15,000 years ago

The Western USA breathed a sigh of relief once the Farallon plate completely disappeared under the North American Plate around 50 million years ago.  The continental basement, full of north-south trending cracks and pent-up tension from the insistent force of the collison, relaxed westward and flexed downward along those lines of weakness.  A simplified version of that is shown in the diagram below…

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Image from the University of Georgia, http://www.gly.uga.edu/railsback/1121Lxr37.html

This had some peculiar consequences for Utah, Nevada, and bits of the surrounding states. You can see this from space!

Basin and Range

ESRI basemap + USGS physiographic province data.

The decompression of the earth’s crust caused a maze of roughly north-south trending valleys and mountain ranges. Additionally, it dropped this whole area to a level where water could not get over the Sierra Nevadas to the Pacific or the Continental Divide to the Atlantic.  The Basin and Range Province became a giant version of the Great Divide Basin where water can only flow into its local valley and evaporate, and the Great Salt Lake is the poster child.

The formation of the Basin and Range landscape isn’t anywhere near done, to the dismay of city planners in Salt Lake City. Utah’s capitol sits right on top of the fault zone where the Great Salt Lake’s basin is sporadically sliding down the edge of the Wasatch Range. This is evident along the edge of the mountains where you can see (geologically) recent fault scarps from the highway.

faults and landmarks

Everything right of the brown lines is rising, and everything to the left is sliding down…

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My photo didn’t come out, so here’s a better one from TaylorScienceGeeks with yellow arrows pointing to the faults I saw from Hwy 215

In the Little Cottonwood Canyon part of the Wasatch Range, to add insult to injury, a giant blob of magma rose from the tail of the subducting plate 30 million years ago and punched through the already disheveled layers of sedimentary rock. Most locals refer to the rock as the “white” or “Temple” granite, but the smooth, bare cliffs are actually made of a relative of granite called quartz monzonite that has less quartz and a more even balance of two kinds of feldspar minerals. This massive batholith (geology-ese for “giant blob of magma), now unearthed by millions of years of erosion, is currently home to some world-class rock climbing routes and a Church of the Latter Day Saints top-secret genealogy bunker.

 

I couldn’t manage to get a good photo of the Little Cottonwood formation without the car door in it, here’s a beautiful one from seekraz.wordpress.com (c) Scott

On the way back down the valley it was easy to see traces of the latest force of nature in the canyon. During the last glacial maximum 15,000 years ago, the road we drove on would have been under hundreds of feet of ice! Both Big and Little Cottonwood canyons were occupied by huge glaciers fed by precipitation fueled by the ancient Lake Bonneville, driven up the mountains by western winds, and dumped in the Wasatch Range as snow. As these well-fed rivers of ice scraped downhill they carved out the dramatic steep-walled valley that we see today. The piles of pulverized rock shoved ahead and to the sides of the glaciers remain at the mouths of the canyons and are now mined as construction fill. The same climate pattern bears out today, with a warmer average temperature and a smaller lake, as the powdery snow that Scott loves to shred down at Snowbird.

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If you were wondering, the cable car ride to Hidden Peak is totally worth it, and not just for the thoughtful signs!

On Thursday, with my car still up in the air, Scott took my dad and me downtown to see the famous monument built out of Little Cottonwood Canyon’s quartz monzonite – The Church of the Latter Day Saint’s Temple Square.

When the congregation outgrew the original temple they moved to a giant structure that could hold 20,000 Saints at a time and has a forest on the roof! In order to avoid the weight of organic soils up there, the engineers used ground-up shale from the Wasatch Range to anchor the plants and  then pile on the fertilizer.

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Scott and I with the guide

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Pulverized shale “dirt”, at 1/3 of the weight of the real thing

 

Just as we were leaving the conference center I got the call saying that my car was ready to roll again. That afternoon we said goodbye to Scott and Salt Lake City, and headed north to a very different landscape indeed. Goodbye mountains, hello giant lakes of (cooled) lava!

Stay tuned for Road Trip Part 4: Snake River Plain and Columbia Gorge.

References:

“Glad You Asked: How Was Utah’s Topography Formed? – Utah Geological Survey.” Accessed October 25, 2017. https://geology.utah.gov/map-pub/survey-notes/glad-you-asked/how-was-utahs-topography-formed/.
“Little Cottonwood Canyon – Utah Geological Survey.” Accessed October 25, 2017. https://geology.utah.gov/popular/places-to-go/geologic-guides/virtual-tour-central-wasatch-front-canyons/little-cottonwood-canyon/.
“Wasatch! Part 1 – Geological Evidence of a Fearsome Fault.” The Trembling Earth (blog), May 8, 2013. http://blogs.agu.org/tremblingearth/2013/05/08/wasatch-part-1-geological-evidence-of-a-fearsome-fault/.
Eldredge, Sandra N. The Wasatch Fault. Vol. 40. Utah Geological Survey, 1996.
“Knowledge of Utah Thrust System Pushes Forward – Utah Geological Survey.” Accessed October 30, 2017. https://geology.utah.gov/map-pub/survey-notes/knowledge-of-utah-thrust-system-pushes-forward/.

 

https://seekraz.wordpress.com/tag/white-granite-mountains/

Road Trip Part 2: Wyoming’s Great Divide Basin

Day Three: Boulder, Colorado to Salt Lake City, Utah

We headed out of Boulder early in the morning, and as my father drove first I clutched my thermos of tea and looked over the map for the day. I hadn’t ever looked at southern Wyoming with any interest before, but we were going to be driving through most of it. The mountain ranges and high plateaus in Wyoming were created by the same processes that created the Colorado Rockies: the Laramide Orogeny that elevated the American West between 70 and 60 million years ago. The atlas had the Continental Divide marked in bright yellow, and to my surprise it seemed to acquire a split personality just north of the Sierra Madre Mountains, skirt a vast empty area on the map, and then reunite south of the Wind River Range.

A few hours later I took the wheel in Rawlins, and signs announced that we were crossing the Great Divide for the first time today and entering the Great Divide Basin.

Day 3 itinerary

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Welcome to the Great Divide Basin! A whole lot of flat sage brush 7,000 feet in the air…

If I had poured out my thermos onto the ground in Rawlins, it would eventually flow towards the Atlantic.

If I dumped that same tea out in Green River, on the western side of the Great Divide basin, it would flow towards the Pacific.

But if I poured it out by one of the many oil derricks dotting the Great Divide basin… it would go pretty much nowhere.

So why does the defining drainage divide of the continent have a hole punched in it in the middle of Wyoming?

Google was less useful than usual on this question, so I had to wait until I got my journal access through Oregon State (SCORE!) to do some serious database sleuthing. And even there I couldn’t find much – I guess there aren’t many scientists considering the middle-of-nowhere Wyoming. However I did find a 2010 article by Paul Heller, Margaret McMillan, and Neil Humphrey at the University of Wyoming and University of Arkansas that presented a potential cause.

These authors propose that the Great Divide Basin originally drained through Sand Gap, on the northeast side of the basin, to the Platte River around 50 million years ago in the early Paleogene period. (shown in figure 1 below) They based this on a comparison of bedrock elevations at the 4 most likely historic outlets of the basin.

Heller et al figure 1 captionHeller et al figure 1

The next crucial step is climate: The high elevation but relatively low relief of the Wyoming basins meant that they have gotten little precipitation throughout the past 50 million years compared with the neighboring high peaks to the east. This leads to a difference in erosion between the basin areas and the majority of the area of the North Platte River headwaters and watershed. More sediment was removed north and east of the Great Basin, causing the Earth’s crust to bounce back in those areas by a few hundred meters over millions of years. The science-y ways to name these processes are differential erosion and isostasy.

By around 10 to 8 million years ago, this uplift east and north of the Great Divide basin tilted the basin to the south just enough that water no longer had any reason to flow out of Sand Gap. Instead, it flowed into lakes with the basin itself and evaporated, causing the saline soil that confounded settlers’ effort to cultivate the area. Figure 6 from Heller et. Al, below, shows the direction of that tilt…

Heller et al figure 6Heller et al figure 6 caption

Going back to the tea theme earlier in the post, I found it easier to think about this in terms of a teacup (the Great Divide Basin) with a chip in the edge (Sand Gap) on a balance (the earth’s crust). This is a farfetched analogy, but hang with me here. In the beginning the balance is evenly weighted – tea is poured into the teacup and flows out the chip in the side, and there is an equivalent weight on the opposite side of the balance that keep the bar level.

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However as weight is removed by the North Platte River from the northeastern side of the balance, the opposite side tilts down to the southwest. In this tilted position the bottom of the chip is at a relatively higher elevation than before, and with the cup being refilled less often than previously tea can no longer flow out of the chip. Instead it evaporates there and leaves behind residue, much like what I find on Monday morning when I don’t wash out my mug before leaving my grad student office on the previous Friday…

After almost two hours of driving through the basin we drove past the sandstone formations of the Rock Springs uplift and passed the *other* continental divide into the Green River Basin.

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Around the Wyoming/Utah border we started descending from the Rocky Mountain plateau down into the Basin and Range geologic province. The western side of this plateau gets relatively much more rain, so we saw our first tree-covered mountains since Laramie earlier in the day!

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Unfortunately, my valiant little Honda Civic had some seriously weird noises going on after we swerved and braked hard to avoid an accident that day.

The downside: We had to spend an extra day in Salt Lake City while a mechanic checked it out.

The upside: We have family there, and they had the time to take us up into Little Cottonwood Canyon in the Wasatch Range to play tourist.

More details about the fantastic landscape around the Great Salt Lake to come in Road Trip Part 3!

Source Cited:

Heller, Paul L., Margaret E. McMillan, and Neil Humphrey. “Climate-Induced Formation of a Closed Basin: Great Divide Basin, Wyoming.” Geological Society of America Bulletin 123, no. 1–2 (2011): 150–157.

Petit Jean State Park: the nerdy perspective

To minimize my off-topic rambling, I’m covering my trip to Petit Jean State Park in two posts: Petit Jean State Park: the outdoorsy view about the hiking, and this one to cover the geology we saw along the way! This second post one may make more sense if you read the first one before it.

“So in the beginning there were the Ninja Turtles, and then the extra Ninja Turtles, and then the volcano erupted and BAM! They got stuck!” That hypothesis spilling out of the mouth of the Boy Scout behind me on the trail seemed like a pretty logical idea actually, given that we were staring at a rocky meadow filled with fractured stone domes the size of small cars.

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Let’s zoom back out for a moment.  We need some perspective to see what these turtles are made of, where they are, and why they’ve been able to hang around.

Geologically, Petit Jean State Park lies in the Arkansas Valley region of the state, sandwiched in between the faulted, tortuously folded rocks of the Ouachita Mountains to the south and the flat pile of sedimentary rocks that form the Ozark Plateau.

Arkansas geologic regions

Geologic regions of Arkansas – the park location is mark with a star. Yellow colors indicate unconsolidated sediment, greys and blues are conglomerates and igneous rocks, light green is sandstone, darker green is shale, and blue is limestone.

Because of this pressure from the south, the layers of sedimentary rock around the park are gently folded into shallow syncline ( U-shaped) and anticline (n-shaped) structures. The axis of these folds is perpendicular to the source of pressure, so the folds create east-west trending lines on the surface. Closer to the Ouachita Mountains the pressure exceeded the rocks’ ability to deform into folds; they broke along faults, like the Ross Creek faults on the right-hand side of the image below.

petit jean cross-section 2

Information taken from the Arkansas Geological Survey maps for the Atkins and Adona Quadrangles

The Pontoon Syncline creates the bowl-shaped plateau that the park rests in. From above, the plateau looks like the head of a bird overlooking the Arkansas River.

Petit Jean Mountain Bird

I couldn’t resist messing with the USGS topos…

This topography closely mirrors the underlying geology of the park, showing where the Arkansas River and Rose Creek have broken through the tough sandstone “cap” of the plateau. (Arkansas Geological Survey map of this view can be found here)

Petit Jean specific geologic map crop

The geologic map for the Adona Quandrangle below covers the southern part of the park, and highlights the trails that Jackie and I explored. In the zoomed-in box, you can easily see how Cedar Creek is carving back into the resistant Hartshorne sandstone that caps the plateau to expose the weaker Upper Atokan shale below. Click on this sentence to go to the Adona quadrangle map PDF courtesy of the Arkansas Geological Survey.

Detailed geology of Petit Jean

Nowhere in the park is the stratigraphy more defined than at Cedar Falls! There’s a clear boundary visible between the pale sandstone at the top of the falls and the darker shale at the bottom.

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Up-close and personal with the contact between the Hartshorne sandstone and Atokan shale

During the early Pennsylvanian period when these sediments that would become these sandstone and shale rocks were deposited, central Arkansas was submerged under a shallow continental sea. The Atokan shale and Hartshorne sandstone are separated by an eroded gap in the record that erased years of sediments – an unconformity. Their composition tells a story of a changing depositional environment: it was in a coastal swamp or underwater and filled in with fine-grained muds from around 315 to 311 million years ago (mya), ended up above water either by uplift or a dropping sea level around 311 mya, and the re-covered by a blanket of sand deposited by meandering river systems and deltas from approximately 311 mya to 307 mya.

The sandstones and shales in this park are about 10 million years younger than the similar rocks I’ve profiled in Giant City State Park (Illinois Basin), and about the same age as those  I climbed on in the Red River Gorge area (Cumberland Plateau).  They all belong to the Carboniferous period from 299 to 359.2 million years ago.

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Background paleogeographical of the Early Pennsylvanian Period map copyright of Colorado Plateau Geosystems.

The Carboniferous period is defined by huge jungles of ferns and early trees that flourished in the high oxygen levels, and then were buried to for the coal that now powers our industrialized lives (Carboniferous = Latin for “coal bearing!). You can’t find coal in Petit Jean State Park, but a few fossil traces of this era remain! The best-known fossil location in the park, along the Cedar Creek trail, was covered by an intermittent stream when we were there but signs along the Cedar Fall Overlook boardwalk also give visitors an introduction to the first drafts of trees that once grew here.

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Beside the fantastic views from the top of the plateau, there are two smaller-scale geologic features that make this park awesome to explore: the “carpet rocks” and those “turtle rocks”!

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Like sandstone rocks in the other two parks, the Hartshorne sandstone contains the dark, wavy, resistant iron formations called Liesegang banding. Unlike the other parks, though, Petit Jean sits on the northernmost fringe of rocks deformed by the rising Ouachita Mountains between 290 and 245 million years ago.  This pressure created geometric series of cracks in the sandstone, and when water enriched by tiny iron-rich hematite, goethite, and magnetite particles entered these cracks it left behind a cement stronger than the surrounding rock. As the weaker rocks are the iron-rich cement was worn away, it left behind the crazy raised pattern of the carpet rocks. Unfortunately the best examples were underwater when I visited the park, but here’s a photo from the Arkansas Geology website:

Petit Jean State Park: Carpet Rock

You can also see subtler version of them in the cliffs in the first 1.5 “map miles” on the Seven Hollows trail (eastern part of the trail).

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The most striking geological feature of this park isn’t found anywhere else – the turtle rocks! No real (or Ninja) turtles were harmed in their formation. The Arkansas Geological Survey blog describes them as:

“unique, mounded polygonal structures that resemble turtle shells.

The processes that generate “turtle rocks” are not clearly understood. One explanation suggests that these features were created by a process known as spheroidal weathering, a form of chemical weathering that occurs when water percolates through the rock and between individual sand grains. These grains loosen and separate from the rock, especially along corners and edges where the most surface area is exposed, which widens the rock’s natural fractures creating a rounded, turtle-like shape.

Additionally, iron is leached from the rock and precipitated at the surface creating a weathering rind known as case hardening. These two processes along with the polygonal joint pattern contribute to this weathering phenomenon.”

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These turtles rocks exist at the very top of the plateau, and at the top of the ridges.  This is different than at similar sandstone “caps” on the landscape in temperate regions, like in the Red River Gorge, where the top of the formation is relatively smooth and even. Water is relentless in finding the most efficient path downhill and these turtle rocks, with their crazy honeycomb drainage pattern, defy shortcuts. My idea is that the turtle rocks only exist at the top of the because of the nature of stream drainage patterns, stream flow, and the speed of that flow.

It’s pretty intuitive that intermittently wet ditches feed into into small creeks, which flow into medium-sized streams, which combine to form rivers. On the quantitative side of hydrology this is represent by the “stream order” systems classified as 1, 2, 3…. where order 1 streams have no regular tributaries, order 2 streams have 1 tributary, etc. By definition, in a given watershed order 1 streams are at a higher elevation that order 2 streams (there’s no cheating gravity!), and the stream order increases with decreasing elevation.  By the the time water organizes itself into something that a hydrologist would give an order number it has carved out a regular depression in the terrain that it reliably flows through.

Reliable flow, though, would be lethal for a turtle rock. They only exist because the force of water can’t yet overwhelm the intrinsic weirdness of their structure. A little water emphasizes the shape of the rocks by removing small amounts of sand slowly enough that it doesn’t erase the maze of fractures and cracks that define the turtles’ shells. Because of this, they can only remain at elevations above the highest order 1 stream, where rainwater hasn’t organized itself into defined channels yet.

However they were formed, they give the landscape a surreal Dr. Seuss-ish touch that’s really delightful. And just down the trail from the turtles, there’s a patch of tafoni “honeycomb” weathering interspersed with Liesegang bands that reminds me of a village in “All the Places You’ll Go!”. I know it’s made by pockets of easily dissolved minerals like salt or chalked weathering out of harder sandstone and ancient iron deposits, but my inner eight-year-old sees a miniature cliff dwelling…

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Petit Jean State Park crams so many whimsical rock formations, fossils, and cliff-top views into a relatively small piece of land. It makes for a wonderful field trip!

For more information on the park’s unique geology, check out:

“The Geologic Story of Petit Jean State Park”, a field guide written by Angela Chandler

The entry for Petit Jean Mountain on the Encyclopedia of Arkansas