Sweet Rocks in the San Juan Islands

If you like orcas, Canadian layered bar cookies, and rocks that are related to said cookies, read on!

Like many families in 2020 and 2021, mine had multiple false starts trying to plan this vacation during the brief periods of 2020 when society was trying to come to grips with how much we’d have to shut down to protect our communities. But finally in July 2021 the van Stolks made it happen. We loaded up a rental car and boarded the ferry to Friday Harbor on San Juan Island to kick off four days of hardcore relaxation.

My sister and I decided to surprise our parents with a whale watching tour with Maya’s Legacy. We thought it would be a nice nerdy cruise with naturalists even if, as the staff said, we weren’t guaranteed to see whales. Boy were we ever the luckiest though! More on that later. We left from Friday Harbor and cruised around the path on the map below.

Map of our wildlife tour itinerary – see top right for spoilers 😉

The boat cruised past the north coast of Flattop Island to admire the varied lounging positions of happy harbor seals. While we were at it I also admired the stunning layered rocks the seals were sunning on. These neat layers of nearshore sandstone, cobble conglomerate, shale, and storm deposits were laid down on some foreign coast during the Cretaceous period. That foreign coast collided the western shore of North American in the late Cretaceous between 100 and 84 million years ago. This process is very similar to what I wrote about in my post about the Oregon Coast – we meet accreted terranes once more. The San Juan Islands are a whole series of geologic immigrants, separated by five large thrust faults.

So I looked up this formation when I got home in my handy “Roadside Geology of Washington” and had to laugh. That layered formation is part of the Nanaimo Group. If that name is familiar, you likely know it from a layered Canadian treat with a nutty chocolate graham cracker crust, vanilla custard, and chocolate ganache.

A very scientific comparison (c) Courtney.

The rocks in the Nanaimo formation (pronounced nuh-NYE-moh) occur north of the most northerly thrust fault in the San Juan Islands, the Haro Fault. This fault shares a name with the Haro Straight – the boundary between Canada and the US. These rocks on Flattop island have more geologic allegiance to the Canadians than to the rest of Washington State, but with desserts like Nanaimo bars in the game you can’t blame them.

The sediments that make up the Nanaimo group eroded off of a large accreted terrane/mini-continent named Wrangellia that makes up most of Vancouver Island and southern Alaska (think of the Wrangell Mountains) as it was colliding with North America between 90 and 65 million years ago. Coarser sediments were deposited when sea levels were lower, and fine grained sediments were laid down as sea levels rose. Between the sporadic movement of the terrane and other causes of sea level change such as glaciation, the sea levels varied enough to result in frequent flips of sediment type.

Not my MS paint cross section – Steven Earle of Malaspina College drew this cross section of the deposition of the Nanaimo Formation.

After greeting the seals and the rocks at Flattop Island our captain Dave aimed for a pod of orcas he heard was northwest of Sucia Island. This small island looks like an absolute paradise for kayak-camping, and is made of the Eocene sedimentary rocks that got eroded from the mainland side of the Salish Sea and layered on top of the Nanaimo group. These rocks are the orange layer labeled “tertiary rocks” on Steven Earle’s image above. Dave threaded the boat past the high stone reef north of Sucia Island where more seals sat with their heads just above the waves. We join a couple other tour boats as they followed a family of orcas on the hunt! There was one more professional hanger-on in contrast to us tourists- a NOAA scientist with a net trailed behind the pod in a little boat to scoop up anything interesting left over from their prey.

Lee the naturalist ID-ed the whales by comparing their fins to a digital yearbook of locals. This family was Biggs orcas (formerly known as transient orcas), distinguished by their preference to hunt mammals like seals and smaller whales. We followed this family for a little while, all starry-eyed about beating the 80% chance of seeing the Puget Sound’s most famous residents. Then Lee and Dave decided to take a risk and turn the boat west to try and find another pod they had heard of. The boat made a beeline towards the oh-so-scenic Phillips oil refinery. But here in shallow water we found more orcas!

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Mama and baby orca, and the big male orca circling our boat!

Tours have limits on how close we can move towards them in a boat, but the whales kept swimming closer. And closer. Eventually Dave killed the motors on the boat so we wouldn’t have a chance of hurting them. We lost sight of them for a moment until the boat started rocking and a HUGE male orca appeared within a wave beside the boat. A second later, in the next wave, we saw the face of a juvenile harbor seal who knows he’s in big trouble. He dove away and in close succession the large male, two adults, and two juvenile orcas started circling the boat. But where was the seal now?

Turns out he was an intelligent and resourceful seal, so he lodged himself safely between our boat’s propellers where the whales couldn’t grab him.

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He rested there for 10 minutes or so while the guide considered shooing him away. He ended up disappearing on his own accord. The guide said he dived and can out-compete the whales in a breath-holding contest. The whales eventually moved west with us in search of an easier dinner. I loved how the baby whales were frolicking around doing little belly flops out of the water! Talk about an ideal day.

Last but not least – a review of Nanaimo bars. After consulting with my mom (an authentic Canadian), she says that the one I bought was about 6 times the size of the Nanaimo bar she grew up with. This makes so much sense! I couldn’t come close to finished the bar in one sitting – the white layer has a texture in between cake icing and fudge. Basically pure sugar sitting on top of a coconut, chocolate, and almond crust. Topped with a layer of chocolate ganache. A delicious sugar overload to share with friends.

Resources:

• Geology of San Juan Island and environs: https://www.dnr.wa.gov/Publications/ger_ofr2003-17_geol_map_rocheharbor_100k.pdf
• Information about Nanaimo Group: https://web.viu.ca/earle/mal-cut/nanaimo-group.pdf

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Ireland: Rocks of Newgrange

This post is the last in a series that covers last summer’s van Stolk family trip to Ireland. Here’s the highlight map to get you oriented:

We don’t know much about the people who built the massive passage tomb at Newgrange over 5,000 years ago. They left no written record, and we can only guess at how they used the ritual passages aligned precisely to the winter solstice. However one thing is obvious – they had a particular eye for beauty and detail.

How do we know this? The story is all in the rocks. Black and white, rough and smooth, plain and intricately carved. The massive “kerb stones” along the bottom of the monument were not shaped by human tools except for detailed swirling patterns created with small chisels. The builders must have scavenged all over the countryside for boulders of the appropriate size to decorate. And many of the rocks come from dozens of miles away!

Swirling patterns on a kerb stone

Bright white quartz cobbles from the Wicklow Mountains (near Glendalough, which I wrote about in the last post), dark speckled granodiorite cobbles from the Mourne Mountains, and dark gabbro cobbles from the Cooley Mountains form designs on the outer walls of the monument. Smooth greywacke from Clogherhead in County Louth forms the inner passageway and outer kerb stones. Finally, the interior of the huge mound was built up from local gravel from the banks of the Boyne River.

Keep in mind, Newgrange was built before the invention of the wheel made it to Ireland. Archaeologists think that the rocks were carried as far as possible by boat before being loaded onto log rollers or sledges to get to their final destination.The 97 kerb stones each weigh at least a ton, and it’s estimated that Newgrange contains 200,000 tons of stone. These ancient people committed themselves to a serious labor of love!

Archaeologists debate the period of time that people used Newgrange as a spiritual and cultural site. However they agree that it was “lost” around the 5th century and then rediscovered at the turn of the 18th century when a local landowner went looking for stones to expand his buildings. Amateur “antiquarians” from around the British Isles visited the site from its rediscovery in 1699 to the 1920s. A formal archaeological survey started in 1962 and was complete in 1973. During this process, the tomb was “restored” to the way that we see it today by educated (and controversial) guesswork. The researchers found the cobbles piled down by the base of the mound and posited that they had originally been pressed into the side of the mound as a kind of retaining wall.

So who make sup this cast of characters? Distances measured in ArcMap, from a generalized geologic unit to Newgrange assuming that the builders used boats as much as possible to transport the rocks.

Quartz: Distance traveled: about 65 miles. These are the same quartz veins that I wrote about in my Glendalough post!

Gabbro: Distance traveled: about 35 miles. This is a dark coarse-grained intrusive igneous rock.  It’s the most plentiful rock in the ocean’s crust, and when found on land is associated with rift zones where continents have torn apart from each other. It has the same mineral composition as basalt (like at Giant’s Causeway) but cooled slowly underground instead of solidifying quickly above the surface. It’s mostly made of the black mineral pyroxene, with smaller amounts of white plagioclase feldspar and green olivine. This gabbro even shares the same age and source as the Giant’s Causeway – about 60 million years old, and formed when Pangaea ripped apart to form the modern Atlantic Ocean.

Granodiorite: Distance traveled: about 40 miles. This rock is very much like granite but has a different balance of the two feldspar minerals. It has more plagioclase feldspar that granite does, and so appears whiter. This contrasts strikingly with the black amphibole and pyroxene minerals in the rock, so granodiorite puts me in mind of a dalmatian’s color scheme. The other kind of feldspar, orthoclase, can add a pinker tinge to granite. The Newry Granodiorite complex crystallized in the Caledonian period – about 400 million years ago – as a byproduct of the closure  of the ancient Iapetus Sea.

Graywacke: Distance traveled: about 15 miles. This particular kind of sandstone forms in deep marine environments when undersea avalanches, called turbidity currents,  mix up all sizes of particles – silt, clay, sand, and gravel. This rock was formed during the Silurian period between 433 and 419 million years ago, and got shuffled to the surface since then.

I can only wonder what these rocks meant to Newgrange’s builders. Some thoughtful ancient travelers noted their favorite rocks around the island, and decided that they ought to be a part of their community’s treasure. I think we might have gotten along.

Resources:

https://en.wikipedia.org/wiki/Newgrange

https://www.ancient.eu/Newgrange/

Granodiorite at the Mourne Mountains: http://www.mournelive.com/how-the-mournes-were-formed.htm

Gabbro on the Cooley Peninsula: http://www.3roc.net/assets/CooleyPeninsulageology.pdf

 

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.

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.

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.

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.

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.

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.

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.

Image from: http://homepage.usask.ca/~mjr347/prog/geoe118/geoe118.054.htm

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.

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.

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.

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.

 

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.

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.

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

Ireland: Mining’s legacy in Glendalough

After Heather and I explored Brittany we headed north to join 35 other van Stolks and their partners in Ireland for a family reunion. No, we aren’t Irish, but the Dutch family wanted to vacation outside of the Netherlands and the American part of the family wanted to spend time in a scenic part of northern Europe. Ireland was a delightful compromise. We converged on a holiday cottage complex just north of Dublin where we spent a convivial time moving from porch to porch catching up on years of news. The whole bunch of us set out in a rather unruly convoy to highlights like Newgrange, Slane Castle, and a sheep herding demonstration further afield in Glendalough.

Glendalough is a jewel of a lake in the mountains south of Dublin in County Wicklow, a rugged contrast to the gently rolling green hills usually associated with Ireland. We all oohed and aahed at the sheepdogs and their  puppies, and then a smaller group of cousins set out on a hike to work off the cabin fever.We did the “white trail” around the upper and lower lakes at Glendalough. It’s a stunning 7.8 mile loop! We did it counter-clockwise, which results in a gentler upward climb. If you hike this clockwise you have to climb up the hundreds of wooden stairs on the eastern side of the lake… not my idea of a great time. Going counter-clockwise also results in beautiful views of the monastery site from the top of the cliff!

Trail map from Alltrails.com

It turned out to be a lesson in the importance of looking at the scale of the contour lines on the topographic map at the visitor’s center. We thought “oh, we only cross one topo line on the map, the trail must stay close to the lake.” Well it turned out that the distance between topo lines on that map was 0.4 kilometers – about 1,500 feet. My cousins with a strong aversion to heights were absolute troopers. The views from the top were amazing!

Hanging out in a textbook-perfect glacial valley, with the old mine buildings in the background. Halfway to the top!

At the top! Two cousins aren’t in this picture because they didn’t fancy spending more time at the top of this cliff than absolutely necessary and they also are much fitter than the rest of us.

The southern cliff is topped with blanket bogs. They’re an extremely soggy and sensitive landscape, so the park put in a couple miles of boardwalk to minimize human impact. I felt like I was somewhere in Tolkien’s Middle Earth!

Glendalough seems like a valley outside time, once you step away from the tourist shops. The paths take you by an old monastery, streams in strange mossy landscapes, and the lake itself surround by hills and forests. It came as a surprise to me when we found the remnants of an abandoned mine at the eastern end of the lake.

It turns out that between the 1790s and the 1920s this area a hive of mining activity. You can easily tell what the miners were looking for in the landscape – the scars of white quartz rubble are the giveaway (see the slope on the right side of the photo above). The miners were looking for lead, silver, and zinc. Specifically, they found it in the minerals galena and sphalerite.

Image of galena (dark gray) and sphalerite (orange-ish brown) in quartz (white) from the Glendalough mine from the National Museum of Ireland.

Galena is a mineral composed of equal amounts of lead and sulphur (its formula is PbS). In this area silver substitutes for lead in the crystal structure around 5% of the time, making it a valuable ore for silver as well as lead. Sphalerite is made of equal amounts of zinc and sulphur (formula is ZnS). But how did they get here, and why are they only found in the quartz?

Let’s take a step back an look at the history of the local landscape over the past few million years, courtesy of an interpretive sign at Glendalough’s ranger center. The information is great so I didn’t bother re-typing it, but you may have to click on the image and zoom to read it if you’re reading this on your phone.

 

Photo of an interpretive sign of Glendalough’s geology at the ranger center.

Two types of rocks form the foundation of this landscape: a metamorphosed version of mudstone or shale called schist, and the granite which muscled its way up into those rocks during the Caledonian orogeny. Remember that from a few blog posts back? This Irish granite is a cousin of sorts to the granite that became the Mont Saint Michel. It too was formed as the heat created by the collision of Laurentia, Baltica, and Avalonia created magma that rose up into overlying rocks and cooled into huge lumps of granite (called batholiths in geologist jargon). In the map below, the granite is shown in red. It also shows just how many mines were once active in this area!

A map of mining activities near Glendalough – we hiked past #7 and #8, Glendalough Valley mine and Van Diemen’s land mine. This map also shows the geologic contrast in the region between the schist (light pink) to the east and the granite (red) to the west of the lake. This map is from https://secure.dccae.gov.ie/GSI_DOWNLOAD/Geoheritage/Reports/WW065_Glendalough_Glendasan_Glenmalure_District_Overview.pdf

This particular batholith is called the Leinster Granite batholith and underlies much of County Wicklow. It’s harder than the surrounding schist and creates more rugged cliffs when assaulted with millions of years of wind, rain, and glaciers. In the Wicklow mountains the granite slopes tend to be covered in boulder fields, and the schist slopes are covered in heather and other creeping low bushes. Neither type of rock weathers into particularly inviting soil for plants, at least not in the geologically short period since the last Ice Age.

Rock specimens that I couldn’t resist at Glendalough: Schist with neat protruding flexible sheet of mica (left), granite (center), bits of waste quartz from the mining operation (right)

Here’s a map of the mine site that is #7 on the map above, and the first area we came to on our hike. This map was put together by the educational group “Glens of Lead”. This group put up some great historical signs in along the park about how the old mining operations worked.

And here’s a map of the second area on the hike, #8 on the map.

Very little of the original infrastructure remains today, except for the stone buildings at the Glendalough mine site and the bright white quartz of the tailings rubble from the mines. The shafts and tunnels have been blocked off and the old tramways completely dismantled. The site seems very wild again.

Standing on the schist side of the valley, looking over to the steep granite cliffs and the piles of quartz tailings below the exits of the old mine shafts 1,000 feet below.

Above right: granite with vein of hydrothermal mineralization (foot for scale) in the mining area, compared with schist exposed at the top of the cliff on the south side of the lake.

But how does lead ore get into quartz veins? I’ve written about continental collisions and granite before in this blog, but not really about smaller processes of metamorphism. It’s time to fire up MS Paint again.

Magma bodies (red) rise off of the subducting oceanic crust and cool into intrusive igneous rocks (pink). Water (blue speckles) in the oceanic crust allows the crust to melt at lower temperatures than the surrounding rock, and travels upwards as a part of the magma. Diagram by C. van Stolk.

Back around 300 million years ago, the ocean Iapetus was closing as the old continents Laurentia, Gondwana, and Avalonia moved towards each other. The oceanic crust under Iapetus had to go somewhere; it subducted under the continents. After a few million years of being underwater that oceanic crust was pretty soggy as rocks go. The conveyor belt of plate tectonics drove the heavy oceanic crust down under the lighter continental crust.  It began to melt as it sank beneath the continent and into the upper layer of Earth’s mantle called the asthenosphere.

It turns out that this water trapped in the crust is kind of the “secret sauce” of metamorphism. The presence of water allows rocks to melt at lower temperatures than they would otherwise. Metamorphism boils down to two variables – heat and pressure. Both increase vertically with depth in the earth’s crust. Pressure also increases horizontally in collision zones. In the presence of equal amounts of heat and pressure, wet rock will melt to a greater degree than dry rock.

Anyone who has taken a ride in a hot air balloon learns that heat rises – the hot air in the balloon keeps the passengers aloft in the cooler surrounding air. The blobs of magma rising from the subducting wet oceanic crust are much like extremely dense, slow-motion hot air balloons – they rise through any weakness they can find in the surrounding cooler and drier rock. The blobs of magma become batholiths of intrusive rock when they cool, like the granite here. As the granite cooled, the heat had to go somewhere, just as the oceanic plate had to go somewhere as the ocean closed. The magma “cooked” the shales that surrounded it into the metamorphosed version – schist (see purple “contact metamorphism” on the diagram below). However the story of the water that magma contained isn’t over.

If water can’t fit into the crystal structure of the magma as it cools into intrusive igneous rocks, it is released from the melt. It takes along ions that can be dissolved in it and travels into cracks in the surrounding rock. Often these “cracks” are caused by faults or by joints caused by horizontal pressure. One of the most common elements carried along this way is silica, which in combination with oxygen forms quartz veins as it cools. This mineral-rich hot water is called a “hydrothermal solution”.

Diagram of hydrothermal alteration from https://opentextbc.ca/geology. (a) Shows a magma body that has risen into cooler rock and is “cooking” it shown by the purple aureole. (b) Shows magmatic water being released from the magma body through veins. (c) Shows how groundwater moving past the magma body can also carry dissolved minerals away from it to other locations.

As the hydrothermal solution rises and cools, minerals form out of the solution like rock sugar forming out of hot sugar syrup as it cools down. Not every part of the solution is really well mixed – some parts of the solution are like oil and water and stay somewhat distinct as they travel together. Examples of this are silicate minerals (i.e. quartz SiO2, feldspar KAlSi₃O₈ – NaAlSi₃O₈ – CaAl₂Si₂O₈) and sulphide minerals (galena PbS, sphalerite ZnS). As the solution cools, these two types of minerals form adjacent but separate structures.

So here at Glendalough, you have granite and schist cut through with veins of hydrothermal rocks that contain chunks of sulphide ore minerals in the more abundant quartz. The miners followed these hydrothermal veins to find the valuable ore, and discarded the attractive but comparably worthless quartz in tailings piles at the site after the rock was put through a huge crusher to break out the softer sulphide ore minerals. I was sorry to notice that they were so thorough that a casual geologist really can’t find any of that ore nowadays.

I was happy enough to take away great memories, beautiful views, and a few new rocks in my pocket.

Resources:

A good brief history of the mines here: https://www.mindat.org/article.php/368/A+History+of+Glendalough

Brief intro to geology of Glendalough here: https://www.wicklowmountainsnationalpark.ie/nature/geology/

https://www.gsi.ie/en-ie/geoscience-topics/geology/Pages/Geology-of-Ireland.aspx

detailed geological survey of mining in the region: https://secure.dccae.gov.ie/GSI_DOWNLOAD/Geoheritage/Reports/WW065_Glendalough_Glendasan_Glenmalure_District_Overview.pdf

detailed geological survey of mining at Glendalough specifically: https://secure.dccae.gov.ie/GSI_DOWNLOAD/Geoheritage/Reports/WW025_Glendalough.pdf

geological map of Ireland: https://secure.dccae.gov.ie/GSI_DOWNLOAD/Bedrock/Other/GSI_BedrockGeologyOfIreland_A4.pdf

Maps of lead mining in the area by the local education group “Glens of Lead”: https://www.avenzamaps.com/vendor/209/glens-of-lead

More about the Iapetus Suture, which connects the half of Ireland/Scotland that was once Laurentia (proto-North America) with the half that was once Avalonia (proto-Europe). https://en.wikipedia.org/wiki/Iapetus_Suture

Interesting map of the terranes that make up Ireland: http://www.askaboutireland.ie/reading-room/environment-geography/physical-landscape/Irelands-physical-landsca/the-formation-of-the-phys/

Ireland through geologic time: https://www.gsi.ie/en-ie/education/the-geology-of-ireland/Pages/Ireland-through-geological-time.aspx

Specimen of galena in quartz from the mine: https://www.museum.ie/The-Collections/Documentation-Discoveries/July-2016-(1)/Lead-Bearing-Minerals-from-Glendalough

More about contact metamorphism/hydrothermal alteration/sulfide ore bodies

Contact metamorphism with good diagrams: https://opentextbc.ca/geology/chapter/7-5-contact-metamorphism-and-hydrothermal-processes/

http://www.geologyin.com/2014/11/veins-and-hydrothermal-deposits.html

Overview of sulfide ores: https://uwaterloo.ca/earth-sciences-museum/resources/hydrothermal-minerals

Cliffsnotes version of hydrothermal metamorphism: https://www.cliffsnotes.com/study-guides/geology/metamorphic-rocks/hydrothermal-rocks

Detailed review of ore genesis, including immiscible solutions. https://courses.lumenlearning.com/wmopen-geology/chapter/outcome-ore-and-mineral-resources/

Mazes of mines and catacombs beneath Paris

The Sacré-Cœur Basilica was swarming with tourists on the first day that Elaine, Heather, and I set out to explore it. The line for entry stretched all the way across the plaza and we could hear the muffled din of the crowds within the sanctuary spilling out through the doors. We made a unanimous decision to avoid the chaos by heading to the quieter sanctuary of the nearby Musée de Monmartre. It’s dedicated to the artists and cabarets that gave the neighborhood its bohemian reputation at the end of the 1800s, and was the last place I though I’d find anything geological. But lo and behold, it had a small exhibit on the gypsum mines that used to be active on the Montmartre Butte, as sketched by the Impressionists.

These mines complicated the construction of the Basilica that we had considered visiting that day. In the 1870s the Parisian government committed to building a huge Catholic monument there as an unmistakable reminder of the power of church and state. Montmartre had been the birthplace of the radical socialist Commune movement that had unsuccessfully tried to overthrow the government in 1871, and the government wanted to remind the neighborhood of who really called the shots. However before the structure could rise above the surface, the foundation required 83 pillars sunk 130 feet deep into the rock layers below the gypsum mines.

I had something of an epiphany (or more accurately, and “oh, duh!” moment) – gypsum is the main ingredient in “Plaster of Paris”! So that’s where it came from! In particular, it came from the green areas on the map below:

Montmartre is clearly visible as the ring-shaped cluster of gypsum mines and the center top of the figure. map translated from French by C. van Stolk. By Plan: Émile Gérards (1859–1920) BnF Notice d’autorité personneDigital copy: ThePromenader – Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=28798468

 

Most of the pale building stone that makes the City of Light so distinctive actually comes from within its limits! It gave me a sense of the huge scale of mining in the city that most of what we see on the surface came from underneath it. The gypsum was mined extensively beginning in the Middle Ages to create fire-resistant covering for wooden structures. You can see the distinctive cream or yellow-ish limestone in almost all of the buildings in Paris built before the 1770s, from the Saint-Germaine church to the grand mansions between the Marais and the Place des Vosges. The limestone is riddled with little cone and spiral shaped fossils too, if you look carefully.

These quarries have been active since the Romans occupied what they called Lutece, but the city didn’t get its wake-up call until 1777 when a gaping sinkhole swallowed an entire city block near what’s now the Place Denfert-Rochereau. That’s when King Louis XVI banned mining within the city limits. He also commissioned Paris’s first mine inspector, Charles-Axel Guillaumot, to map the warren beneath their feet and shore up the weak places to prevent a repeat of the “Place d’Enfer” disaster. M. Guillaumot earned the nickname “the savior of Paris” and was one of the few royal appointees of that era to survive the guillotine – the revolutionaries considered him too useful.

Around the same time, Parisians realized that the former quarries posed a solution to another pressing problem – unmanageable overcrowding at cemeteries above ground. Between 1785 and 1814 the bones of over 6 million people who had died since the founding of the city were disinterred and moved in nocturnal religious processions into the properly sanctified sections of the tunnels designated as the municipal ossuary or catacomb just outside what was then the southern boundary of the city. The catacombs were opened to the general public for tours in 1810.

119 years afterwards, Elaine, Heather, and I set out to wait in the long line to enter the Municipal Ossuary a.k.a. the Catacombs of Paris. It’s a rare attraction that appeals the Elaine’s love of spooky things, my love of rocks, Heather’s interest in history, and all of our pressing interest in getting out of the 97 degree heat. We just managed to get into the last tour group before the gates closed for the day! Because of the time crunch we had to fly through the geology exhibition in favor of getting to the creepy bits but I took photos of the placards, some of which I have translated below. For photos of the ensuing Super Spooky Aesthetic ™ check out my travelogue post.

The rocks below Paris are younger than the rocks we clambered on in Brittany – they’re from the Eocene era between 56 and 38 million years ago, when the Paris Basin held a shallow sea that left behind characteristic limestones and shell fossils. The sea went through periods when it very nearly dried up, leaving layers of evaporate minerals such as gypsum.

Image photographed by author at the catacombs, legend translated

North-south tectonic pressures slightly buckled the basin in the time since the rock was formed. This created the Meudon anticline (A-shaped fold) on the southern side of Paris, which is why limestone and gypsum from different ages are mined at similar elevations on either side of the Seine.

Image photographed by author at the Catacombs, and subsequently translated

Left: labeled layers in the limestone, Right: teensy 5mm stalactites!

Paris has a thriving community of “cataphiles” who risk law enforcement action to explore the subterranean side of the city. National Geographic did a great special on them in 2011. Over the years since the quarries were abandoned in the 1950s, they’ve made the flipside of Paris into their playground and undertaken mapping efforts. Here’s an elegant map of the “Great Southern Network”, with notes and annotations. It’s the kind of treasure map that got me into cartography in the first place.

If you’d like to learn more, Dr. Jack Share at one of my favorite blogs “Written in stone, seen through my lens” wrote two fantastic, extremely detailed posts about the geology of Paris – one focusing on the gypsum quarries and the geologic origins of the Paris Basin, and a second one on the mines and catacombs. I highly recommend those posts, and the entire blog!

Postscript:

We did eventually visit the Sacre Coeur Basilica towards the end of our stay in Paris. It turns out that the basilica is quietest directly after services in the evening, and there is a lovely organ postlude. From the inside it’s a wonderfully peculiar building. Sacre Coeur was built between 1875 and 1919 and the stained glass windows weren’t added until after WWII, and so it encompasses huge changes in the French design aesthetic. The architecture is a mix of the stately Neo-classicical style like the Pantheon and the Byzantine revival style, it got a gloss of whimsical Art Nouveau statuary at the turn of the century, and ended up with weird abstract stained glass windows from the post-war period when artists felt that the world was broken beyond repair. The building is made of travertine from the Souppes-sur-Loing quarry, in the Seine-et-Marne department about 100 km south of the basilica. Travertine is an exceedingly hard, fine-grained stone that releases chalky white calcite when it rains. So basically, it’s self-cleaning and is able to stay gleaming without pressure-washing!

English-language resources:

https://en.wikipedia.org/wiki/Mines_of_Paris

Paris: From quarry to catacombs

http://catacombes.paris.fr/en/history/geology-and-quarries

http://www.sacre-coeur-montmartre.com/english/history-and-visit/article/architecture

A really excellent post about the mines of Montmartre: http://written-in-stone-seen-through-my-lens.blogspot.com/2014/04/geological-legacies-of-paris-basin-part.html

Another very thorough post from that same author on the rest of Paris’ quarries: http://written-in-stone-seen-through-my-lens.blogspot.com/2014/06/geological-legacies-of-paris-basin-part.html

reddit post hosting an AMAZING map of all the explored catacombs under Paris: https://www.reddit.com/r/MapPorn/comments/b50j1r/detailed_map_of_the_paris_catacombs_in_english/

French-Language resources:

detailed post on mines, mining techniques, and mine inspection in Paris: http://exploration.urban.free.fr/carrieres/index.htm#exploitation

Crazy pink rock formations at the Cote du Granit Rose

Part 2 of the geology of my summer vacation. For an idea of where this fit in our trip, check out the travelogue post. This post follows the first post on Mont Saint-Michel.

I had left all of the vacation planning in Heather’s able hands so I could focus on my thesis last spring. My only requirement (only halfway in jest) was that the vacation had to include eating pastries on rocks. And boy, did Heather deliver! Days 5 and 6 of the trip found us near Trebeurden and Ploumanac’h on the fabulous pink granite coast. The sun was shining, the pain au chocolat was as delicious as I had ever hoped for, and a giant granite playground awaited us.

my dreams came true!

There isn’t a shortage of granite on the Brittany coast – we met some in the last blog post too. Much of was grey and only visible in isolated outcrops. As we hiked east from the little port of Ploumanac’h along the coast, the grey granite gave way to crazy piles of unmistakably pink rock! I couldn’t help but start wondering what caused the change in color, not to mention the weird shapes!

It turns out that the explanations come in threes: the pink granite is made of three minerals, it belongs to one of three different igneous events in the region, and three different substances have sculpted the granite into the wild shapes at Ploumanac’h.

The pink granite gets its rosy hue from potassium feldspar, while the greyer granite has more creamy-colored plagioclase feldspar in its makeup. I illustrated their mineral composition in the figure below. The natural history museum in Ploumanac’h informed me that the pink granite is  approximately 50% potassium feldspar, 30% quartz, and 20% biotite. They didn’t give details about the less glamorous grey granite and I was too focused on getting to the pink stuff to even take a close-up of it, so I’ve only approximated its composition.

Both colors of granite at Ploumanac’h were put in place around 300 million years ago (mya) during the last gasps of a mountain-building event as the ancient continents of Gondwana and Laurussia crashed together to form Pangaea. I talked in depth about this massive game of continental bumper-cars in the previous post, so I’ll skip it here. Over time erosion unearthed the buried masses of granite, as shown in the figure below.

Photo of a diagram in the exhibit at the Maison du littoral, text translated by me.

To get even more specific, the granite in the area was put in place in three physically distinct phases around 300 mya. In the first phase, two magmas with different compositions intruded the surrounding metamorphic rock at the same time. The first was rich in silicon and formed the coarse-grained pink granite and the second was poor in silicon and formed the dark gabbro visible near Tregastel. These two igneous rock types melted in the same event from two different types of source rocks, giving them their unique compositions.

During the second phase, another silica-rich magma forced its way into joints in the now-cool first pink granite. This magma had a similar composition  to the pink granite in the first event but cooled more quickly than its predecessor, forming smaller mineral crystals.

In the third phase, a magma with a more basic (as in pH) composition intruded into an dome-shaped weakness in the cooled granite from the first two phases. This magma cooled into the blue-gray granite near Ile-Grande.

translated by me, original images found at : http://ville.perros-guirec.com/fileadmin/user_upload/mediatheque/Ville/Maison_du_littoral/refonte_page_environnement/expo_origine_du_granit_roseBD.pdf

The difference between the colors of the ~520 million year old granite at Mont Saint-Michel, the ~300 million year old grey granite at Trebeurden, and the ~300 million year old granite at Ploumanac’h isn’t merely ornamental. The rocks’ mineral compositions give geologists clues to the kinds of source rocks that melted into the granite. Feldspars and quartz have high silicon:oxygen ratios in their composition, and so indicate that abundant silica was present in the source rocks.

A whole host of different kinds of minerals are built from silica and oxygen, ranging from the densest minerals with 4 oxygen atoms  for every 1 silicon atom to the less dense minerals with only 2 oxygen atoms for every 1 silicon atom. In general, the less dense silicon-rich minerals are more represented in the continental crust, while the denser silicon-poor minerals are more common in the oceanic crust.

You can see these relationships between minerals’ properties and igneous rock types below in the igneous rock classification chart every mineralogy student learns by heart by the end of the term. It’s only a guideline – if a mineral was missing from the source rock, it will not show up in the igneous rock created from its melting. For example, amphibole and muscovite are missing from the pink granite.

Image from https://www.routledgehandbooks.com/doi/10.1201/9781315152929-3

This indicates that the pink granite was formed predominantly by the melting of low-density, high-silica rocks at low melting temperatures. The grey granite at Trebeurden is a little bit to the right of the pink granite on the classification chart – still a granite, but including more minerals with higher melting points and less potassium feldspar (a.k.a.  orthoclase feldspar). The gabbro at St. Anne is even further to the right, and likely formed from the melting of a chunk of oceanic crust. Sometimes rocks are completely off this chart. For example the magma that formed the pale granite that we saw at Mont Saint-Michel either melted at low temperatures (geologically speaking) of ~600 C or melted from source rock whose chemistry didn’t allow for the formation of dark mica or amphibole crystals.

So I figured out why the granite was pink instead of grey. But what created its otherworldly shapes? And where did all these boulders come from?

Usually boulders are created in steep landscapes where chunks of rock falling off the canyon walls are tumbled aggressively in mountain streams and carried long distances. In contrast, these boulders have barely moved relative to each other since the granite cooled! They were formed in place by erosion, shown in the diagram below. The technical French term for this formation is “un chaos”, which seems very appropriate.

The important factor here is a change in the rate of weathering and erosion. In this case, the erosion regime changed from slow dissolution of the rock by groundwater (shaping the granite into boulders underground) to more rapid erosion as the waves crash on the shore (exposing the boulders).

Once the boulders are exposed to the elements, two slower types of chemical erosion nibble them into even more convoluted shapes. Chemical reactions between salt spray and the the mica and feldspar crystals in the rock transform them into weaker clay minerals that wash away, creating divots and creases in the rock wherever salt collects.

As saltwater works on the rocks from the top, organic acids in soil eat away at the rocks at ground level over tens of thousands of years to create subtle mushroom shapes.

The end result is an utter delight to explore!

Heather points out a quartz vein in the pink granite. The boulder on the center left shows a distinct salt weathering divot on its top.

Climbing to the top of a formation, I found a 2-foot deep crenelated “crow’s nest” formed by salt weathering!

Sources (all are in French):

Great summary from the local natural history museum, the Maison du littoral: http://ville.perros-guirec.com/fileadmin/user_upload/mediatheque/Ville/Maison_du_littoral/refonte_page_environnement/expo_origine_du_granit_roseBD.pdf

Less technical summary from the local tourist board: http://www.cotedegranitrose.net/la-cote-de-granit-rose/geologie-le-granit-rose/

Long and extremely thorough field trip guide published by the Geological and Mineralogical Society of Brittany: https://sgmb.univ-rennes1.fr/geotopes/decouvertes/23-decouvertes/67-ploumanac-h

Short summary/technical field trip guide: http://www.saga-geol.asso.fr/Geologie_page_conf_Ploumanach.html

 

Why can Mont Saint-Michel withstand the tides?

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)…

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:

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.

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??”

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.

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.

Around 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.

Image from https://throughthesandglass.typepad.com/through_the_sandglass/2009/09/montsaintmichel-a-massive-sedimentology-experiment.html

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!

 

Map from http://www.projetmontsaintmichel.fr/les_travaux/hydrosedimentaire.html

translation of the text box:

• 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

Twin Trek 2019: France!

This is a “travelogue” post – more geology specific posts to follow!

My sister and I had a fantastic opportunity for out annual “Twin Trek” this year! My family was having a reunion in Ireland, so our transatlantic plane tickets were covered… it opened up a whole new continent of possibilities. I handed all the responsibility for choosing a destination over to Heather, pleading that I didn’t need such a tempting distraction while finishing my thesis. I told her that as long as I could eat pastries while sitting on rocks at some point I would be happy. She’s a gem and put together a fantastic itinerary in France! Both of us had studied abroad in the south of France in college, and she had spent a year teaching English in Normandy. This time, she decided that we would explore a beautiful region that she had briefly visited and wanted to return to – Brittany, in the northwest. We hostel-hopped from Rennes to Mont-Saint-Michel to St. Malo to the Pink Granite Coast to Finisterre, then back to Rennes and on to Paris. Being over 25 and being able to get a rental car felt so luxurious… the last time we were in France as college students we got an education in foreign public transit out of necessity.  I created an ArcGIS Online map of our route and have included a link to it below (unfortunately, free WordPress accounts can’t embed maps). I love the new watercolor base map that is available! The link is followed by screenshots.

(You can reach the map of our trip location directly at this link)

I’m looking forward to writing several posts about this trip. I’m sure the research will stretch my command of the French language in new directions, but it will be a fun scavenger hunt to see what information I can find!

1. What geologic features allow Mont-Saint-Michel to rise above the tidal flats?
2. Why is the granite in Ploumanac’h and the rest of the “Cote de Granit Rose” so pink?
3. When created the spectacular white cliffs near Camaret-sur-Mer on the Presque-Isle de Crozon?
4. Why are there so many sea caves near Morgat, also on the Presque-Isel de Crozon?

But in this post, I’ll just share the travel diary part of the story.

I was cranky, jet lagged, and hadn’t slept in 20 hours when Heather picked me up from the train station in Le Mans. I’m not sure which one of us was more frazzled – she had spent the previous few hours reintroducing herself to driving stick shift in a tiny car on tiny roads after six years driving exclusively an automatic. So as glad as we were to see each other it was a very quiet car ride to Rennes, where we checked into the hostel and went in search of Brittany’s specialty: buckwheat crepes filled with delicious things. We felt significantly better about the state of the world when our food arrived, accompanied by traditional Breton teacups of hard cider.

Rennes was a wonderful place to recover from jet lag and feel like I was truly in France. Brightly painted timber-and-plaster houses lean crookedly against each other like they’ve had too many teacups of cider and surround gothic-style churches and squares full of cafe tables. After getting lunch (crepe-wrapped sausages) at the huge Saturday market at the Place des Lices, Heather and I wandered through the shopping district to the Jardin de Thabor. Once a monastery garden, the public gardens got a scenic 19th century renovation to include paths, grottoes, a botanic garden, and a delightfully random aviary. The lawns were packed with people escaping un-airconditioned apartments to catch breezes in the shade. We parked ourselves on a shady bench by the rose garden to finish the rest of the basket of strawberries. By that time my internal clock was in revolt. I went back to the hostel to crash until Heather lured me out of the room with promises of  new kinds of crepes and a glass of rose.

The next day we set out on the Twin Trek in earnest. Heather was excited to finally see Mont-Saint-Michel in sunny weather, and I was curious as to whether it would equal the hype. It turned out that getting there early on a Sunday was a great decision – the tour buses from Paris must have been running late because there were pleasantly few other tourists there. We could really imagine that we had stepped back in time. The stories on the audioguide of the Abbey made the small fee well worth the money. There aren’t many interpretive signs to bring the impressive but stark walls of the abbey to life; the audioguide explains not only the construction of the abbey but the history that it witnessed and the lives of the religious orders that lived there. We had lunch on the ramparts beside a family of seagulls who watched us with great interest and eventual disappointment when we refused to share.

Heather and I headed back to the car once tour groups started to flood the island in earnest – the small streets were so crowded that we had trouble elbowing our way back down to the gate. We drove to the storied port town (and pirate hideout) of St. Malo, settled into the hostel, and walked down the beach’s boardwalk to find a crepe place in the historic walled city. It’s amazing – the city was 75% destroyed during WWII, but was painstakingly rebuilt stone by stone so it looks unchanged since the 1600s! We missed the last bus back to the hostel and stayed to watch the Bastille Day fireworks. The fact that the sun set at 11 pm was really throwing me off!  Especially because we had big plans for the next day – a hike from St. Malo to Port Mer along the coast.

We took the number 8 bus to the Ilots stop, and then hiked the GR (Grand Randonee) 34 to Port Mer where we caught the bus back to the hostel. We weren’t using a map, but it turns out that it was over 11 miles. It was a hot, sunny day and the coast was beautiful – all sheer cliffs, ruined castles, and sailboats tacking between tiny islands. Also, as it turned out, nude beaches. So despite the ocean views, there were some parts of the route where we chose to admire the landward side of the trail. I’ve included an interactive web map below. Although it may look like we walked on water, those parts of the route actually indicate tidal flats. There’s such a huge tidal range here! When we left at the morning the sea was a between 1/2 mile and 1/4 of a mile away from the boats stranded on the tide flats, and in the evening the boats were floating. Heather and I agree that we would recommend taking the bus one stop further to La Guimorais to get straight to the prettier parts of the hike.

(You can link directly to the interactive map here)

After a well-earned dinner and beers at Port-Mer, we took the bus back to St. Malo and slept very well that night. If you weren’t doing this hike in the summer, you’d have to go all the way to Cancale to catch a bus back to St. Malo – the bust line that serves the beaches is seasonal.

After a morning exploring the ramparts of St-Malo and hunting down ermine-themed souvenirs, we started the drive west to our next hostel in Trebeurden on the Cote de Granit Rose. Once we reached the hostel, I switched into the driver’s seat and Heather navigated us to the surreal-looking geologic destination that she had been promising me – the pink granite near Ploumanac’h. We had a leisurely happy hour, hike, and dinner while watching the sun slowly set over the Channel.

We met more opportunistic seagulls while eating our picnic dinner on the pink granite

Heather hanging out with a “chaos” of pink granite boulders in the background. The boulder had been sculpted into crazy shapes by water and wind!

The next morning, I dragged Heather out of bed bright and early so that we could go back to the geologic museum I had seen at the Maison Littorale along our hike the previous evening. It gave me plenty of material for a future blog post on the granite we were scrambling over, and the Heather bought me a lovely small piece of polished local granite from the gift shop as a birthday present. She knows me well, and yes I am literally that person who fills their suitcase with rocks. In my defense, it wasn’t much bigger that a bar of soap. The museum also had an exhibit on how the park was trying to restore vegetation, so Heather and I tried to be good stewards when we were using the boulders as adult-sized jungle gyms. There were still plenty of rocks and tide pools that we could get to appropriately! The tide pools here look different than the ones in Oregon – the coralline algae is grey instead of pink, and the predominant anemones are smooth, dark, and glossy instead of rough and green.

It was hard to drag ourselves away from that amazing coastline, but we also know we needed to make it to our next stop that night. We had lunch with the chickens at the hostel, loaded up the car, and drove a two hours to the small fishing port Cameret-sur-Mer on the Presque-Isle de Crozon. We went on a hike before dinner with a plan to explore a surrealist poet’s ruined mansion, and menhir alignment, and the Point de Pen Hir. Along the way, we stumbled across a huge complex of WWII bunkers and sobering memorials to the 638 French merchant marine ships and many Bretons lost in the war.

The next day dawned grey and cloudy, and Heather had planned for us to hike near Kerloc’h and then rent kayaks. That original plan was foiled when the boat rental shop told us that the westerly wind was too strong to rent kayaks from Kerloc’h, and so we went to Morgat on the opposite side of the Cape de Chevre where the wind was more favorable.The day was still cloudy and cool when we hauled our kayaks to the edge of the tide flats. That rental staff looked at us like we were crazy and suggested renting wetsuits, but the sun came out a few minutes after we launched! It turned into an absolutely perfect day to be on the water. The wind was still unpredictable though – one sneaker wave tossed Heather and her kayak into a complete somersault as she was pushing off from a beach, scraping up her arm and scattering her belongings across the waterline. She maintains that it was OK because getting a scar at sea ought to make her an honorary Breton pirate.

Relocating our kayak adventure to Morgat had a major unexpected silver lining: sea caves!! The coastline was steep, convoluted, and carved into fantastic arches and caverns. When the tide is high you can paddle into some of them…although the incoming tide created significant whitewater in some of them. Heather and I had a blast surfing the waves in the more exciting caves but it may not have been the smartest thing to do. When a family with small kids on the bows of their kayaks asked us where the “Devil’s Chimneys” were, we crossed our fingers behind our backs and feigned ignorance.

Th next day, the clouds of the previous day turned into genuine Breton downpours. We gave up the idea of outdoor adventures in favor of taking a bouncy ferry ride across the inlet to the huge port of Brest. Unlike Rennes, it doesn’t have that old-world scenic French flavor. It was bombed completely flat during WWII and hastily rebuilt in cubic concrete except miraculously for one thing – the ancient fort. It now houses the French naval offices and also a great maritime museum. I wish I could have teleported my dad there to enjoy the exhibit on around-the-world racing in catamarans for the Jules Verne Trophy.

The next day was pretty tame… we poked around the many art galleries in Camaret-sur-Mer, and then drove back to Rennes. The following morning we took the train to Paris to meet up with Heather’s girlfriend Elaine.

While it was relatively warm in Brittany, the “canicule” (poetic French term for heat wave) was merciless in Paris during the five days of our stay. A change from the usual atmospheric patterns caused more hot air than usual to push its way north from the Sahara into countries much worse prepared to deal with it. The daily high temperature ranged from 97 to 108 degrees F , while the average high for July is 78. This forced us to change our usual travel patterns and take a more relaxed approach to Paris than we had planned. We made it through the week with strategic applications of siestas, Orangina, and ice cream.

Over the course of the visit the three of us visited the Pantheon (mercifully cool, and with a fascinating exhibit on deaf history), the Musee d’Orsay (packed, but worthwhile for the amazing exhibit on Berthe Morisot), Sacre Coeur (overrun by tourists diverted from the closed Cathedral de Notre Dame, and quieter directly after services), Musee de Montmatre (an quiet oasis well worth the admission cost with delightful exhibits about impressionists and the neighborhood), and the Catacombs (Elaine’s favorite for the Spooky Aesthetic ™, and a standout for me for the ancient history of mining). I’ll definitely write another post about the elaborate system of mines and tombs under Paris!

On the last day of our stay, we successfully navigated a packed metro with our luggage, Heather led the way to the most well-hidden municipal bus depot I’ve ever encountered, and we headed north to meet my parents and visit my grandmother in Belgium. Thank heavens the bus was air-conditioned.

Can’t I just teleport back to Ploumanac’h?

Next up: geology posts.

After that: Ireland!

Sisters visit South Sister (and Green Lakes)

This post covers Day 2 of the Annual Twin Camping Trip: for Day 1 check out Smith Rock Hike: Volcanic Rocks, Volcanic Heat.

Heather and I woke up bright and early on a chilly morning to get a head start on the popular Green Lakes trail up to the base of South Sister, one of a trio of snow-capped volcanic peaks west of Bend. We hiked Trail 1.7 (traced in yellow on the map below), and stopped for lunch at a very scenic overlook (red dot). Including all our side jaunts, it was a 11 mile round-trip hike with about 1,000 feet of elevation gain from the trailhead to the lakes. We were three thousand feet higher here than at Smith Rock, so thankfully it was much cooler.

Fall Creek is aptly named – and it’s absolutely beautiful!

 

 

Just when the ponderosa pines and waterfalls are starting to become routine, the view opens up onto the jagged slopes of the Newberry rhyolitic dome from South Sister’s most recent eruption 2,000 years ago. Although it looks inhospitable it actually is a perfect home for a variety of adorable rodents. A little pika and several yellow-bellied marmots stuck their noses out of the rubble to say hello. Too far away to photograph, alas, you’ll just have to take our word for it. Heather said that the lava flow looked like Mordor from the Lord of the Rings… maybe a lair for the ASBOG Balrog?

Pika, photo from the National Wildlife Federation

Marmot, photo from Wikipedia

These lava flows blocked the Fall Creek drainage thoroughly enough that debris and water built up behind them, creating the spectacular Green Lakes!

Almost there…

The very top of North Sister peeked up above the flanks of South and Middle Sister in this shot

Heather contemplates how much work it would take to bring a kayak up here…

As we sat to eat lunch at the overlook we were entertained by the profanity yelled by hikers who decided to gleefully jump into Green Lake only to discover how freezing cold it is, even in August. Let’s just say that when I stuck my feet in the lake to cool off it only took about 10 seconds for them to go numb… I’m not tempted to turn that into a full-body experience.

Ultimate Sisters selfie: Heather, South Sister, and me

We were pretty beat by the time we descended back to the trailhead and happily fell into our hammocks with libations back at Elk Lake. It was another hour or two before we felt like moving again, and we made dinner with the last bits of daylight. Afterwards we took advantage of the clear skies to stargaze – Heather had never seen the Milky Way except in photos. Stupid southeast/east coast light pollution. I’m so glad we could fix that – we had an amazing view not only of our galaxy but of several shooting stars that put on a show! The next morning we packed up camp and headed out on the next adventure to an even bigger volcano: Crater Lake National Park.

But before we leave the Sisters… what were we hiking on?

All three Sisters are part of the High Cascades, the range of distinctive volcanoes in Oregon and Washington that formed between approximately 35 million years ago and the present. I gave a bit of a teaser to their history in my post about Dome Rock in the Western Cascades – I could see the Sisters from there.

Three Sisters Family Portrait, from their USGS Volcanic Hazards website

The Sisters, while linked together by their names, are not triplets. North Sister is by far the eldest; it was formed between 120,000 to 45,000 years ago by basalt and andesite lavas and eruptions. Middle Sister formed between 40 and 14 thousand years ago, but primarily between 25 and 18 thousand years ago, putting it close in age with South Sister. It is built of andesite, dacite, and rhyolite, and is famous for the archaeologically significant Obsidian Cliffs formed in one of its eruptions that became a tool-making bonanza for Native Americans.

Here’s more specific timeline that I drew for South Sister, based on information from the US Geological Survey Volcanic Hazards Program (USGS VHP).

You can get an idea of the wide range of eruption ages in the figure below from the Oregon Department of Geology and Mineral Industries (DOGAMI)’s recreation brochure for the area.

Clip from the DOGAMI recreation map that I edited to show the most recent South Sister Flows from 2,200 to 2,000 years ago: the “Devil’s Chain” flows are in purple while Rock Mesa is outlined in Green. There are so many “Devil’s Whatcha-ma-callit” features in Oregon, some cartographers must have had a flair for the dramatic.

While South Sister hasn’t erupted in two thousand years and the Middle and North Sisters have been dormant even longer, the USGS isn’t ruling out future eruptions.

“The Three Sisters region has hosted volcanic eruptions for hundreds of thousands of years, and future eruptions are a certainty. Two types of volcanoes exist in the region and each poses different hazards. South and Middle Sister are recurrently active over thousands to tens of thousands of years and may either erupt explosively or produce substantial lava domes that could collapse into pyroclastic flows. They could also produce lava flows. In contrast, less explosive eruptions could occur almost anywhere in the surrounding area, and construct small cinder cones to large shield volcanoes made mostly of basalt to andesite lava flows. These volcanoes are typically short-lived (months to centuries) and usually don’t erupt again”

If it’s any reassurance, geologists’ ideas of “a certainty” consider a geologic-scaled timeline up to thousands of years…. so life near the Sisters could well be mercifully boring during our lifetimes.

The hiking here, however, is anything but!

 

 

References:

USGS Volcanic hazards page for South Sister: https://volcanoes.usgs.gov/volcanoes/three_sisters/three_sisters_geo_hist_128.html

USGS VHP page for all Three Sisters: https://volcanoes.usgs.gov/volcanoes/three_sisters/geo_hist_south_sister.html

DOGAMI flier for Three Sisters: https://www.oregongeology.org/pubs/ll/LL-ThreeSistersRecMap.pdf

In the Playground of Giants Green Lake Field Guide http://intheplaygroundofgiants.com/field-guides-to-central-oregons-geology/field-guide-to-the-cascade-lakes-and-willamette-pass-areas/two-can-tango-recent-and-ongoing-volcanism-and-glaciation-in-the-cascade-lakes-area-field-trip-2a/optional-hiking-trails-for-field-trip-2a/

Photo Credit:

(Pika) https://www.nwf.org/Educational-Resources/Wildlife-Guide/Mammals/American-Pika

(Marmot) By Diliff – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=26414860

Many thanks to Heather van Stolk!!

 

 

 

Smith Rock Hike: Volcanic rocks, volcanic heat

Although we’ve lived in different time zones for a while now, my sister Heather and I have been lucky enough to be able to go camping and hiking together once a year… and we kept up the tradition when she visited me in Oregon!

We set our sights on some classic Oregon landmarks that I hadn’t visited yet either: Smith Rock, South Sister, and Crater Lake.

Map background from MapBox.com

Fun sights between Corvallis and Bend… Mt. Washington and a very festive Sinclair dino in Sisters.

While this was technically a camping trip we copped out and stayed in a hostel in Bend for the first night – Bunk & Brew – which made up for its scarcity of showers by offering complementary local craft beer. This splurge was totally justifiable because it enabled us to get up at the crack of dawn to beat the crowds to some crazy geology.

26.5 million years ago a massive volcano blew its top in central Oregon, spewing enough ash to enough to cover the state of Texas in a layer about 2 meters thick. The Crooked River Caldera eruption would have been catastrophic for any living thing in the area… just check out the phenomenal remains in the nearby John Day Fossil beds. However it was a boon for modern climbers, because it created the foundation of Smith Rock State Park!

The figure above shows the extent of the Crooked River Caldera (red shape #1) and the two other small eruptions that created the John Day formation, including the Smith Rock Tuff. However the rest of the region’s tuff deposits form low hills, not huge towers – why is Smith Rock so different? It turns out that location is key. Because the park lies within the original caldera, shortly after the tuff was deposited super-heated water carrying dissolved minerals rose up through it. This cemented the tuff much like dilute glue would stiffen sand, combining the best of both worlds for climbing – the funky irregular texture of tuff and the hardness of a sandstone.

(sign in visitor center)

As the ash from that explosion solidified under its own heat and weight it created a rock type known as “tuff”. While that determines its composition, the park’s tuff owes its shape to a very different eruption that started 600,000 years ago – the Newberry caldera fifty miles to the south. It spewed out enough basalt to cover an area the size of Rhode Island. This basalt reaches all the the to the southern margin of Smith Rock State Park, and since basalt is tougher than tuff (ha!) it trapped the Crooked River, forcing it to erode in one place instead of shifting around as rivers prefer. This constrained erosion created the steep pinnacles that make rock climbers starry-eyed.

The photos below show the two sides of the river – steep basalt cliffs on the left, softer tuff on the right.

 

Someday I’ll get out here with my climbing gear, this summer just wasn’t the chance. Heather and I instead hiked the Misery Ridge trail along the river and up steep switchbacks over the spine of the park. Following very good advice from my friend Kate we decided to do the loop clockwise in order to ascend by the less steep trail and descend on the stairs.

map from AllTrails.com – we did the loop clockwise

The park is littered with strange hollow rocks, like little fairytale huts for the four-legged park residents. Some are large enough to fit humans!

Heather enjoying the shade

These fantastic shapes were formed by pressurized bubbles in molten but rapidly cooling tuff, and have slowly eroded out of the cliffs. There was a whole village of them near the junction of the River and Misery Ridge Trail.

Looking up at Monkey Face from the River trail. Heather christened my head wear “the typical dorky geologist hat”. I have no shame.

Heather couldn’t resist climbing some more rocks before descending the stairs

Temperatures were predicted to get up to 97 degrees that day so we started at 8:30 AM. After a leisurely stroll along the river and a significantly less leisurely struggle up the ridge we reached the top at 11 AM for a celebratory round of gummy candy overlooking the famous Monkey Face formation.

Scores of people were ascending the stairs at noon as we were passing them going downhill. Several people were prostrate on the side of the trail trying to cool down, and most were markedly miserable.  Smith Rock is a popular park on good roads close to civilization (Bend) and the trail is only 4 miles. This might lure visitors into a sense of complacency but it’s not by any means an easy hike. The signs at the trail heads recommended sturdy boots and drinking a liter of water every two hours while hiking – evidently it’s not exaggeration. I guess the trail is called Misery Ridge for a reason.

I may never climb the 5.14 (insanely difficult) route up Monkey Face, but at least I climbed its mini-me on the playground!

After eating lunch and saying goodbye to Smith rock we stopped by an auto shop to address Jo the Adventure Civic’s warning light (she’s never a fan of the climb over the Cascade passes), and then made our way to the beautiful Elk Lake USFS campsite 45 minutes southwest of Bend. We had a much longer hike planned for the next day, so we settled in for some serious relaxation at the lake shore…

Life is tough 😛

Sources:

Field trip guide to the Oligocene Crooked River caldera: Central Oregon’s Supervolcano, Crook, Deschutes, and Jefferson Counties, Oregon by Jason D. McClaughry, Mark L. Ferns, Caroline L. Gordon, and Karyn A. Patridge

Heather’s wonderful photos!