A Tale of Two Sandstones: Giant City State Park

Earlier this month I found myself driving though the hills of southern Illinois, and decided to take an extra time to spend some quality time with the topographic relief and exposed rock that us residents of western Tennessee don’t see very often.  I spent the morning rambling though Giant City State Park south of Carbondale, and didn’t want to leave! I wandered around the Giant City Nature Trail, which is only officially 1.5 miles but probably more like 3 if you take all the side-trails. After that I stopped by the short Devil’s Standtable trail on a whim, and I’m glad I did! It follows the base of a gorgeous cliff line, and has ample opportunities for scrambling and climbing.


This strategically place trail sign with geologic information might dissuade you from exploring further, but take the well-traveled unofficial trail past it to get to a waterfall!

Southern Illinois is a island of rugged terrain in a state where the elevation rarely exceeds “rolling hills”. It barely managed to escape the Wisconsonian glaciation which bulldozed Illinois north of Highway 13, creating prime cornfield habitat north of the highway and a maze of deep valleys, tall sandstone cliffs, and forested ridges south of Carbondale and Harrisburg. All in all, this section feels more like a misplaced chunk of the Ozarks.

It occurred to me, while eating my lunch on top of a stray sandstone boulder, that the landscape look like a miniature version of the Cumberland Plateau 300 miles to the east. (You can see where those rocks come from in my Red River Gorge Post) These sandstone outcrops had the same iron bands, fragmented blocky weathering structure, and selection of trees clinging tightly to their cliffs. This made me wonder – are these rocks part of the same depositional unit as the ones on the Cumberland Plateau, or do they have a different source but just happen to look similar?


A particularly enterprising tree along the Giant City Nature Trail

Callan Bentley did a great breakdown of the geologic features of the sandstone of the park over at the AGU blog. It turns out that the lacy weathering structure that I had been calling “honeycomb” has the snazzy official name of “tafoni”! I don’t think I can beat Callan’s beautiful photographs and blow-by-blow of depositional features, but I couldn’t find a source for my origins question and set out to research it.

It turns out that the rocks I was admiring, clambering on, and using as a picnic bench were part of the Chesterian formation of sedimentary rocks laid down during the second half of the Mississippian period roughly 359 to 323 million years ago. Therefore, they’re roughly the same age as the rocks on the Cumberland Plateau which were laid down during the Carboniferous era (which is divided the Mississippian period followed by the Pennsylvanian Period).

The rocks in Giant City State Park are on the western edge of what’s called the Illinois Basin, a regional depression in the crust exacerbated by large amounts of sediment deposited when the region was covered by a shallow sea until the Late Pennsylvanian period ~300 million years ago. This same sea also covered the area now occupied by the Cumberland Plateau, and its waves crashed against the shores of the vast deltas carrying sediment down from the rising Acadian orogen of the current Appalachian mountains. The rocks in the Red River Gorge of eastern Kentucky aren’t in the same “family” as the rocks in Giant City State Park, in the sense that they don’t share a sediment source, but instead are classmates from different origins maturing together through geologic time.

There was a bit of a speed bump that separated the Illinois Basin from the Appalachian Basin – the Cincinnati Arch. Now, as we get acquainted with this speed bump, there’s something to keep in mind. Although the older Ordovician rocks at its core might indicate that it’s an anticline (a convex fold in sedimentary layers), this cross section has a trick up its sleeve.


This diagram shows a vertically exaggerated cross-section of the types of bedrock in Kentucky, show that the rocks of the Appalachian Basin (Cumberland Plateau) are separated from the rocks of similar age in western KY/Southern IL by the Cincinnati Arch.

The Cincinnati Arch isn’t a fold structure, but a strip of crust that maintained its original elevation  while the regions to the east and west sagged under the weight of sediment that was piling onto them. I couldn’t find primary resources resource to mention why exactly the Cincinnati arch was able to avoid being down-warped by sediments as its eastern and western neighbors were, unfortunately. (If you know more about that, please contact me!)

That cross-section sparked my interest, so I set out to find a paleogeographic map of North America during the Mississippian period when the Illinois Basin and Cumberland Plateau sandstones were being dumped into place. This map shows a reconstruction of the Early Mississippian, so sea levels would have been a bit lower in the mid- to late- Mississippian period when the Chesterian rocks were laid down.  About 1/3 to 1/2 of northern Illinois would have been above the waves.  I fancied it up in CorelDraw to show the arch, basins, and approximate directions of sediment transport into the basins…

Annotated Mississippian Map 4

Looking at the map, you notice that the arrows pointed to the Appalachian basin come from a mountainous region, and the ones pointing towards Illinois come from part of the land surface that’s relatively flat. This is reflected in the depth of sediment with each basin – the sandstone layers in Illinois are thinner than those in eastern Kentucky. Conversely, because the Illinois basin contained a slightly deeper sea with less sediment input it has thicker layers of limestone in the Carboniferous deposits than the Appalachian basin.

The limestone of the Illinois basin is a major economic resource in the area. Driving down Highway 51 leaving the park (sigh…) I passed the Anna Quarry Company, which has been profiting from that ancient Carboniferous sea since 1865. Their 200-acre, 450-foot deep original mining pit was abandoned when it became economically unfeasable (let’s just say, it now has 350 feet of water in it) but they continue to mine new pits on the property to provide raw materials for aggregate, asphalt, concrete, and agricultural lime.


I got some really funny looks as I parked along the highway to take photos…

Anna Quarry

An aerial view of the Anna Quarry in Anna, Illinois

It was a beautiful sunny drive back to Memphis, but I need to drag some friends back to Jackson Falls in this same area to climb soon!


Giant City State Park website: https://www.dnr.illinois.gov/Parks/Pages/GiantCity.aspx

breakdown of geological formations: http://blogs.agu.org/mountainbeltway/2011/09/20/giant-city/

Chesterian sandstone, which includes the rock at the park: http://isgs.illinois.edu/ilstrat/index.php/Chesterian_Series

A retro but generally accurate backstory of the geology of southern Illinois: https://www.ideals.illinois.edu/handle/2142/42765

A more approachable take on the ancient landscapes of Illinonis: https://www.isgs.illinois.edu/outreach/geology-resources/build-illinois-last-500-million-years

Source of KY cross section: https://www.uky.edu/KGS/geoky/beneath.htm

Source of paleogeographic Mississippian map: http://deeptimemaps.com/wp-content/uploads/2016/05/NAM_key-345Ma_EMiss.png

Source for information on Cincinnati Arch: http://ncad.net/Gp/Erla/ErlaGeol.htm

Blog post about Cincinnati Arch: http://historyoftheearthcalendar.blogspot.com/2014/03/march-10-cincinnati-arch.html

Bedrock Geology of Illinois Map: http://isgs.illinois.edu/sites/isgs/files/maps/statewide/imap14-front.pdf

Bedrock Geology of Illinois Strategraphic Sequence: http://isgs.illinois.edu/sites/isgs/files/maps/statewide/imap14-back.pdf



Happy Birthday, GRACE!

NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites had their 15th birthday this week! The mission was only meant to last 5 years, but dynamic duo of earth-monitoring satellites has kept on observing gravitational anomalies from orbit since they were launched on March 16, 2002. NASA put out this graphic to celebrate:

GRACE satellite

So why do we care about gravity enough to collaborate with German’s space agency (GPZ) to spend 127 million dollars to launch a payload into space to measure it more precisely?

  1. If this gravity tugs Grace 1 and Grace 2 out of the perfect elliptical orbit, it can do so with the very sensitive GPS satellites. This gravity data allows us to re-calibrate GPS data to take minute variations in satellite orbit into account.
  2. We can measure inch by inch the slow upwelling of the mantle as the continents rebound after the last ice age.
  3. Satellites calibrate elevation data by assuming that the height of the ocean surface is essentially spherical, but gravitational anomalies (subduction trenches, mid-ocean ridges) can locally affect sea level. Previous satellite missions such as JASON and TOPEX/POSEIDON very precisely measured the distance from orbit to the sea surface but prior to GRACE, trying to figure out ocean current patterns was like trying to guess the the thickness of hair on someones’ head when the person had a bizarre bouffant hairstyle and we had only vague ideas of what the head underneath was shaped like.
  4. My favorite reason – we can track changes in ice caps and water resources such as melting or accumulating ice, floods, and groundwater recharge or withdrawal!

The two GRACE satellites (GRACE-1 and GRACE-2) are roughly the size of two large couches, and are in constant contact via a laser beam which continuously measures the distance between them. If one of the two flies over an area with a large gravitational anomaly it slows down, which either increases or decreases the distance between the two depending on whether the lead or following satellite is slowing down. This distance data is then compared with GPS information of the two satellites that is collected at the same time to create a “geoid” – a vertically exaggerated model of the imaginary topographical surface of the earth where areas with higher gravitational pulls have a high elevation, and the opposite for areas with lower gravitational pulls.


Earth's gravity field as seen by GRACE

Simulation of the geoid, courtesy of NASA Earth Observatory

The image above come from https://earthobservatory.nasa.gov/Features/GRACE/page3.php, which also does a much  better job of describing GRACE and the geoid than I can. When this data is combined with data from other satellites and ground-based systems, it has the illustrious scientific name of the “Potsdam Gravity Potato“, based on the city in Germany where a research team specializes in this melting pot of remote-sensing data.


The 2011 Gravity Potato – but does it taste good with butter and parmesan cheese?


The magic of the GRACE data comes in its 15 years of data. In that time period certain features on the geoid are almost stationary (The Himalayan mountain range, the depression around Hudson Bay where the Laurentide ice sheet depressed the earth’s surface). However, water is heavy and constantly moving, and these satellites give us a quantitative idea of exactly how much mass is shifting (i.e. being melted or withdrawn) without having to deploy squads of intrepid graduate students to take GPS elevation readings all across Greenland.

The University of Colorado –  Boulder created an online platform to explore the GRACE data – click HERE.

GRACE CU Boulder portal

GRACE’s ability to monitor change also gives us an unprecedented look at the invisible water we rely on – groundwater! While we still don’t have a way to take an MRI of the earth a determine the volume of water in an aquifer, GRACE can at least note when an area becomes relatively heavier (aquifer is recharged by rain or snowmelt) or lighter (aquifer is pumped, and the water flows away through rivers to the ocean). Calculating the rate of this change allows us to discover which aquifer systems are declining at rates that could endanger future use.

UC Irvine groundwater storage trends from NASA's GRACE (2003-2013) for Earth's 37 largest aquifers.

Image from the 2015 study by Richey et al. 2015, courtesy of NASA Jet Propulsion Lab

The world map above shows 37 of the most critical aquifer systems humans depend on, and whether their amounts of water in storage have increased or decreased between 2003 and 2015. (For more information click HERE) Decreases are shown in varying shades of red and orange (as in California’s central valley, or northern India), and increases are shown in shades of blue (High Plains aquifer, Murray-Darling Basin). Before GRACE, the only way to approximate this information would be to check hundreds of wells around an aquifer every single month! Compared to the resources needed to drill thousands of wells and employ scores of technicians, $127 million to launch some satellites seems like a steal.


The above map shows a more general view of terrestrial mass change from GRACE data between 2003 and 2009, and was quoted in this article by Dr. Mohammad Shamsudduha, (Institute for Risk and Disaster Reduction, University College London, UK) about groundwater drawdown in northern India, for example.

The dilemma of being a scientist is that the “OMG isn’t it fantastic that we can get all this data to learn about the earth!!” feeling is countered by the “Well darn this data gives us terrible news” feeling. The upside is that the GRACE mission, for the first time, gives us accurate month-by-month information on the state of our ice caps and aquifers. If nothing else this gives scientists a powerful tool to understand natural seasonal variations and tease out man-made changes. If we can’t measure a phenomenon, we can’t accurately improve our reaction to it. I hope that through this data scientists can show policy-makers how we’ve caught ourselves red-handed draining the earth’s accessible water stockpiles, and incite action to preserve what is left.

I was geeking out about these satellites to my sister, who immediately had the same mental image – I just had open up MS Paint to draw GRACE-1 and Grace-2 wearing fluffy, sparkling quinceneara dresses in honor of their 15th birthday. See below for the delightfully ridiculous result.

Satellites in quinceneara dresses

P.S. For more of the nuts-and-bolts mathematical and engineering behind how these satellites work, you can check out this informative circa-2003 internet flashback.

P.P.S. for even more information, check out these links!


CU Boulder geoid team – http://geoid.colorado.edu/grace/about.html



Discovering Geographical Information Systems: Quantum GIS

I had gotten frustrated with creating site maps in AutoCad 12 LT, and yesterday’s field work was postponed because of rain. Additionally, Quantum GIS software is free. This turned out to be a great combination.

Not to bash AutoCAD 12 LT (for non-technical readers – AutoCAD LT is the “Lite” version of a common engineering drafting software program)- it’s been great for creating site maps for industrial clients who can send me their base plans already in AutoCAD format. I add some new layers for their hazardous waste locations and protocols, drop it into my company’s standard frame, and voila. However, I was going back to my company’s decade-old protocol for mapping monitoring wells in AutoCAD and found it cumbersome. In order to make an accurate map I had to take a screenshot of Google Earth, save it, attach it as an external reference file, adjust the raster DPI so it didn’t look like an 8-bit video game, and then set the layer properties so it wouldn’t accidentally be moved while I added feature points. With that done, I had to go back to Google Earth and transfer a scale – and good luck if I had zoomed the map to fit the site boundaries while in AutoCAD. Once the well locations and site outlines were traced, I would delete the base map. I figured that there had to be a simpler way to do this.

I got the decisive nudge towards exploring Quantum GIS from a geologist friend whose specialty is managing complicated Oracle/ESRI ArcGIS systems.   We were having our usual nerdy kind of conversation over dinner on Friday (planetary plausibility of Star Trek, using radar to map the subsurface of Mars, oil pipelines, etc) when I brought up my mapping conundrum. I had been using the free version of Google Earth Pro but it lacked some of the features I wanted, and he suggested QGIS as the next step up.

Quantum GIS (QGIS) can be downloaded here.

I will freely admit that even though I had done some basic cartography in ArcGIS a few years back, I had little idea what to do next. QGIS has a graphical interface comparable to AutoCAD LT, actually – helpful enough but not completely intuitive. Luckily, there’s an instruction video for pretty much everything on YouTube.


Klas Karlsson created a clear, concise, and useful walk-through of a basic project – you can find it here.

Next I wanted to find a general overview of what the software could do – which“A Gentle Introduction to GIS” by T. Sutton, O. Dassau, and M. Sutton of the Department of Land Affairs of South Africa does nicely. This free text serves as an introduction to geographical information systems in general, but focuses on QGIS. It does a good job of making the software less intimidating, answered my questions about the cartography projections I had to choose between,  and gave me a basic view of the analytical capabilities I can learn in the future.

So, to compare map outcomes (…drumroll…):

Estimated water table surface map made with AutoCAD 12 LT:


Versus a map of the same site made with QGIS (client data blurred out):


This landfill in West Tennessee hasn’t had any contamination in the years my employer has been sampling here – good for the planet and keeping my job simple!

For now I drafted the water surface elevation contours and flow direction by hand and then digitized them, as my company has done in the past. However, I know that somewhere in the jungle of optional plugins there’s a way to make QGIS create groundwater contours based on my data points. That’s going to take more than an afternoon’s study to master though, and I look forward to getting to that point!

Advantages to AutoCAD LT:

  • Ability to draw splines/curved lines, easily rotate shapes and text
  • Faster rendering time between zoom frames
  • Option for typed commands instead of click-and-select
  • Format is widely used across engineering and environmental consulting fields

Advantages to Quantum GIS:

  • Base maps are so easy to insert, delete, and switch out!
  • Ease of entering attribute data, and ability to make any variable of that attribute data a visible tag on a feature location
  • Can enter well locations based on the coordinates measured in the field
  • Easy to measure distances
  • Instant scale
  • Instant and easily modified legend
  • Spatial analysis, once I figure out how to use it
  • FREE

After this intro I’m hooked on the possibilities of QGIS. I’m seriously tempted to digitize my hand-sketched field camp maps and start using it for my Phase I Environmental Site Assessment maps…

I definitely have enough left to learn to fill many a rainy day to come.

How do you use GIS in your work and research? I’d love to hear about it in the comments.

I defeated the ASBOG FG!

All three times that I went to the Geological Society of America conferences, I picked up something from the Association of State Boards of Geology (ASBOG) booth. I won a rather nice tape measure from them in 2015. All three times, the booth staff admonished me with “you should take the Fundamentals  of Geology exam before you forget everything you learned in university!”.

And then I found myself thinking in the summer of 2016 – what am I waiting for? I took all the necessary coursework and more that I need to be licensed, I’m working under two licensed professional geologists, why not take the exam and get on the path to making all that work official?

I ordered the RegReview study guide, said farewell to my three-times-a-week climbing gym habit so I would actually make time to study, and got to work.

I really should have taken it right out of college, but wasn’t as rusty as I had feared. Even though I felt like throwing my study guide across the room after the fourth page of ore mineral formulas, studying for the exam actually reminded me why I want to be a geoscientist. One night I was messing around with formulas for mapping groundwater draw-down and projection of cross-sections onto a map view and didn’t realize that it had gotten to be 1 AM. (I had to get up to be at a job site at 6 AM. Oops.) I got to spend quality time with fields like seismology and structural geology that don’t show up often in my day-to-day work.

Not to mention that my sister drew me this gem of a Lord of the Rings/Geology crossover: Meet the ASBOG Balrog.


So that’s how I found myself at 7 AM at the Department of Commerce building on September 30 armed with a calculator, protractor, and 1 liter thermos of steaming hot caffeine. Walking through the door, I could immediately identify my fellow geologists waiting for the exam – plaid shirts, practical shoes, Patagonia vests, and looks of acute anxiety were all giveaways among steady stream of state employees heading to the elevator.

We all walked out of the exam room four hours later, exhausted and convinced that we had failed. Thankfully, today I found out that I actually passed! With acceptable marks in all categories, even the ones I was freaked out about! (I’m talking about you, engineering geology)

When I was studying for the exam, I scoured google and reddit for advice from people who had taken the exam, and couldn’t find much. Much of the advice pertained to the second exam, (the PG), like this excellent blog post over at Accidental Remediation. In the hopes of helping someone like me taking the FG, here are some of the things I found most helpful:

  1. There is no way on earth that you can cram for this exam. I did one chapter per week in the RegReview book, and that was almost pushing it. I should have started studying earlier – the ASBOG website isn’t joking when is says six months in advance.
  2. Take a close look at the application to take the exam. I got taken by surprise by the fact that after I had submitted my exam to my states professional licensing board, and I had to submitted a completely different application and fee to the national ASBOG organization.
    1. step one: State of Tennessee Geologist Licensing Forms (or your state’s equivalent). For Tennessee, this meant filling out two forms: the Geologist FG Exam Application, and the Geologist Course Reporting Form.
    2. step two: after the application is accepting by the state board, that agency will send you a candidate request form that you will need to send, with a check attached, to ASBOG.
  3. The actual exam questions were slightly easier than the ones in the RegReview book, and didn’t need quite as much math. However, they were still by no means easy. Looking back at my university quiz and test questions, the ASBOG questions were comparable to the more difficult 25% of them. They were very similar in difficulty to the questions in the official ASBOG candidate handbook.
  4. Memorize the picky mineral characteristics/formulas and mining terms. They were on the exam, believe it or not.
  5. Don’t underestimate the power of handwritten notes…
  6. …or flashcards, either. If you use the RegReview cards, add in a few additional handmade ones for ore deposit types, water quality standards, dating methods, Bowen’s reaction series, and engineering characteristics of earth materials (elastic properties, etc).
  7. And then working the practice problems a second time.
  8. I don’t recommend bothering to study in the two days immediately before the test. I know I was too keyed-up for any more information to stick, anyways.  Eat well, try to get some sleep, and do thing that clear your head. In my case it was lunch with an old friend and wearing myself out on the rock wall.

Have you taken the exam? What impacts have being licensed (or not) had on your career? I’d love to hear your opinions in the comments.





Water in the wilderness: China’s growing deserts


The Tengger Desert, courtesy of crienglish.com

I ran across an article that took my breath away.

Living in China’s Expanding Deserts: New York Times by Josh Haner, Edward Wong, Derek Watkins, and Jeremy White.

The drone footage of the contrast of humanity and desert, of children playing in the sand and improbable greenhouses, was absolutely beautiful. Finishing it was something like eating a delicious, carefully plated appetizer and then finding out that there’s no main course to follow it.

Don’t get me wrong, it’s wonderful journalism about a region I’ve always been fascinated with. I was left, though, with questions. What was life like there beforehand? Why is the Tengger desert expanding, and how fast?

Many of my questions will probably have to go unanswered, as I understand exactly 0% of the Chinese language. However, I found some interesting further resources on the area.

Another great article on desertification in Inner Mongolia, with more of a focus on economic and environmental drivers of the desertification than the New York Times feature: Waterless World: China’s ever-expanding desert wasteland by Benjamin Carlson

Cue angelic singing, I finally found an scientific article on groundwater resources in this area written in English:

Currell, M. J., Han, D., Chen, Z. and Cartwright, I. (2012), Sustainability of groundwater usage in northern China: dependence on palaeowaters and effects on water quality, quantity and ecosystem health.Hydrol. Process., 26: 4050–4066. doi:10.1002/hyp.9208

One of the lead authors also wrote an article for China Dialogue – The Shrinking Depths Below – that serves as an introduction to his research and an excellent summary.

A thorough break-down of desertification effects and probable causes by region in China can be found over at here at GeoCases.

Further to the northeast of the area covered in the NYTimes article, the coal processing activities which have lead to huge economic growth in Baotou City in Inner Mongolia have also sucked water away from their prior uses. I’m looking for more sources on this, but this GreenPeace video initially piqued my curiosity.


An annual precipitation contour map of China, from http://www.chinamaps.org. Areas in bright yellow to orange have less than 200 millimeters of precipitation per year, and are considered deserts. The area mentioned in the NYTimes article is a bit west of Yinchuan on this map.



Oh, Canada! Part 3: Clay and Quakes

This is the third and final installment of overthinking of my family’s trip to Quebec. Allons-y!

Intro: Oh, Canada!

Part 1: Oh, Canada! Part 1: Monadnocks

Part 2: Oh, Canada! Part 2: Impact

From La Malbaie in the annular trough of the impact crater, our road trip headed northwest along the coast to St. Simeon to catch the ferry.

Reford to Point-de-Saint-Vallier

A small population of beluga whales hangs out in the St. Lawrence. We were lucky enough to see several of them popping up above the waves on the ferry ride!

From the ferry landing at Riviere-du-Loup we headed north to Grand Metis to see one last garden – called either Reford Garden or Jardin de Metis depending on whether you’re an anglophone or a francophone. Elsie Reford set out to build the perfect garden there in 1926, but the rolling terrain on the southern shore of the St. Lawrence wasn’t very cooperative. The local soil is a thick layer of clay with very poor drainage left behind by the Champlain Sea, an extension of the Atlantic left in the depression of the retreating glaciers between 13,000 and 10,000 years ago. The waterlogged clay hosts scenic marshes of lupins and stunted pine trees but is a significant obstacle for the ambitious gardener.

a recreation of the extent of the Champlain Sea ~11,000 years ago, courtesy of Orbitale at Wikipedia

As the Laurentian Ice Sheet retreated around 15,000 years ago its meltwater washed huge amounts of silt to the sea, which combined with marine clay deposits and the natural chemistry of the seawater created a massive layer of clay. As the crust heaved a sigh of relieve at the weight of the ice sheets being removed, that isostatic process gradually lifted the seafloor into dry land.  This garden took a lot of back-breaking work and planning to dig two- to four-foot deep beds, add in drainage systems honeycombed through the impermeable clay so the plants wouldn’t drown, and then fill in the beds with gravel and imported loamy soil. And this was in the early 1900s before Bobcat earth movers!

Mrs. Reford’s results are spectacular, though.

reford 1

Eventually, though, the time came when we had to drag ourselves out of the garden and back onto the road heading south. But we had one last stop before Quebec City – my mother’s friend’s friend Yves was taking care of a Heritage Canada property at Pointe-de-Saint-Valliers and had invited us there for dinner.  Between dinner and dessert we hiked out to the point, where Yves casually mentioned that the cliff jutting out above the tidal flats was rather smaller than it had been because of that earthquake back in ’88.

Wait what, Quebec has earthquakes?!

It turns out that between the area being torn open as the Iapetus Ocean was formed after the breakup of Rodinia, a meteor punching a crater into the crust~342 million years ago, the nearby Appalachians being built as the ocean closed fully to form Pangaea 270 million years ago, the Atlantic Ocean ripping open ~175 million years ago, and the vast weight placed and released by the ice cap in the Pliocene/Pleistocene glaciation, the crust under the St. Lawrence has had a tremendously stressful life.


Fault map image courtesy of Tremblay et al. 2013

All this stress is exhibited as the St. Lawrence Rift System that stretches from the Ottawa-Bonnechere Graben to the mouth of the St. Lawrence. The dramatic escarpment along the northern side of the St. Lawrence Valley was formed by grabens and half-grabens dropping down due to the extensional force created around 450 million years ago, when a carbonate platform collapsed during the formation of the Iapetus ocean. After 450 million years of erosion the resistant granites, quartzite, and marble of the Canadian Shield now make up the footwall of the graben (visible as the 200 meter high escarpment), with younger rocks making up the hanging wall.  Those late Proterozoic to early Paleozoic faults were reactivated with each successive compression or decompression of the crust.

Right now, the crust is still in the process of rebounding and decompressing after the last ice age. That localized expansion of the crust creates friction along those old fault lines – when too much force builds up for friction to resist, the rocks on either side of the faults slip past each other with a violent jolt that creates an earthquake.

In the region we were traveling, these quakes are categorized within the Charlevoix Seismic Zone and the Western Quebec Seismic Zone. Pointe-de-Saint-Valliers sits on the south-western fringe of the Charlevoix Seismic zone, where the weaknesses in the crust created by the meteor impact in addition to the late Proterozoic faults release the rebounding stress after the last ice age.


Imaged edited from the EarthquakesCanada site.

Luckily the fault zones were on their best behavior while we were there.

After that leg of the road trip we spent a wonderful day-and-a-half exploring Quebec City. My mom introduced me to all her favorite haunts from her childhood there. Much ice cream was consumed, because where else can you get maple ice cream with maple sugar crunch and maple cookies?!

On the way back to Montreal to fly out we found the last remaining dinosaurs in Quebec! No dinosaur fossils have been found is this region, as any rocks that might have contained them were scoured away by the ice caps. The youngest fossils in this area date from the Ordovician. But we can still dream, right?


The author joined the intrepid herd of dinosaurs at the famous Madrid 2.0 gas station in St-Leonard-d’Aston, Quebec (exit 202 on the Trans-Canadian Highway)

Bonus: When my sister and I start hanging out, silly things happen. Like a cartoon geologic history of Laurentia.

geologic comic

Oh, Canada! Part 2: Impact

Intro: Oh, Canada!

Part 1: Oh, Canada! Part 1: Monadnocks

The drive through the Charlevoix, the area on the northern bank of the St. Lawrence from Quebec City to la Malbaie, is jaw-dropping and quintessentially Canadian. Anti-moose fences running along the sides of the highway underline fantastic views of the Laurentian mountains where my cousins learned to ski. When the road winds through enough civilization for the moose fences to disappear, the civilization takes the form of adorable clapboard houses with brightly painted accents and laundry drying on the line. The entire landscape looks like it jumped out of a picture book.

charlevoix 1

However, around 342 million years ago was a really terrible span of time to live there.

It’s hard to tell why from the ground. The road from Quebec City dipped down steeply to get to the sleepy resort town of Baie-St.-Paul, climbed up a winding local road to the village of Les Eboulements perched on a cliff, and then wound back downhill to La Malbaie further north. To get to the Quatre Vents Garden, we drove uphill again along the coast north of La Malbaie. Looking at the map, the main highway that we didn’t take sweeps around in a half-circle from St. Paul to La Malbaie following the easy route through the valley.

That’s pretty odd. The rest of the valleys in the area run roughly perpendicular to the coast. Why would a valley do a u-turn and meet the coast on both ends? (valley represented by the white line on the map below)

Charlevoix map

Well, it turns out that this particular valley had some help in the form of a 1.2 mile-wide chunk of rock.

The meteor crashed into what is now the Charlevoix in the early Carboniferous period; scientists’ current best guess is that it struck 342 million year ago with a 15-million year range of error on either side. The impact razed any flora and fauna, flattened the landscape, and created dramatic shatter cone structures in the whatever underlying Ordovician limestone it didn’t pulverize completely.


Image of an excavated shatter cone, courtesy of impact-structures.com


Initially, the crater was as bowl-shaped as anyone would intuitively expect from bedrock that had been punched by a giant boulder from outer space. Over time, however, the center of the crater rose as a reaction to the absence of pressure after the impact. That rebound created the higher elevation where Les Eboulements stands today.

Us humans have this impact to thank for the half-circle of relatively flat terrain between Baie-St.-Paul and La Malbaie, where 70% of the population of the Charlevoix region now resides.


The crater has a much more uniform and gentle gradient, compared to the rugged highlands of the Laurentian Highlands. A RadarSat image of the Charlevoix area, courtesy of the Canadian Space Agency via impact-stuctures.com

But where is the other half of the crater? It was no match for the seismic and glacial stresses of the past 340 million years. Pangaea crashed together 40 million years later and was torn apart 125 million years after that, and between 2.5 and 0.7 million years ago an ice cap took advantage of those faults in the crust to carve away the weak points. When that ice cap shrank, all that glacial melt poured through the St. Lawrence and washed away what was left.

Charlevoix from Quatre vents

The view looking south from Quatre Vents Garden on the northern rim of the crater, across La Malbaie in the sunken impact ring, towards the rebounded area of Les Eboulements.

I wish I had discovered Observatoire de l’Astrobleme de Charlevoix and its awesome geological app before the trip, but if I ever go back I’ll definitely get it!

Up Next: Oh, Canada! Part 3: Clay and Quakes