Geological Field Tripping in Cyberspace
Early April is the time when my Earth Structure & Dynamics class ventures to the Appalachians for a weekend of learning and intellectual companionship. I’ve reported on these academic adventures in this blog many times1. Over the course of two days we roll across Virginia, from the Shenandoah Valley to the Blue Ridge and out into the Piedmont. We make observations and do geology at dozens of outcrops that range from the spectacular to the subdued. We camp in the Blue Ridge foothills — invariably the group camping and fine dining prove to be both positive and memorable bonding experiences.
Montage from the 2017 – 2019 Earth Structure & Dynamics class field trips. The 2018 class is all smiles in front of a spectacular outcrop at the Ragged Mountain Reservoir in the Blue Ridge. The 2017 class deep in thought at a morbid little outcrop in the Scottsville Mesozoic basin. The 2019 class enjoys lunch while in the field. It’s hard to social distance on these field trips.
The Spring 2020 semester is unlike any that has come before, and as a consequence of finishing the semester’s coursework remotely there is no Appalachian field trip this spring for my Earth Structure & Dynamics class. It’s a tangible loss, as it’s difficult to replace the learning packed into that field trip.
But we’re not giving up, the 2020 Earth Structure & Dynamics class is going on a digital field trip to one of the classic stops that we’ve visited for nearly two decades.
To be clear, I’ve yet to be convinced that virtual field trips can satisfactorily take the place of the real thing. The primary learning objective for our weekend class field trip is to practice doing geology in the field. To achieve our goal we make repeated observations and measurements, discuss our interpretations while standing at the outcrop, and learn from our mistakes. Doing geology in the field is difficult, and practice is important.
Our destination for this digital trip is Hidden Rock Park near Goochland. This former landfill was turned into a county park in the late 1990s. As the site was graded to construct baseball and softball fields, large expanses of the bedrock were exposed. Bedrock outcrops are far and few between in the eastern Piedmont and Hidden Rock Park serves as an important destination for William & Mary Geology field trips.
Had we visited Hidden Rock Park, the students would have poured forth from the vans, and working in teams examined the outcrop and tackled a set of questions posed on the ‘always popular’ field worksheets.
What follows are a set of pictures (taken over the past 15 years on W&M field trips) from Hidden Rock Park that might be serviceable enough to answer the questions on the worksheet.
A view to the south-southwest on the big outcrop at Hidden Rock Park (2019).
View of a sub-horizontal (nearly flat) part of an outcrop at Hidden Rock Park. What rock types are present? Red pocketknife is ~10 cm in length.
View of a sub-horizontal (nearly flat) part of an outcrop at Hidden Rock Park. What structures are X? Red pocketknife is ~10 cm in length.
It takes teamwork to measure the orientation of foliation at Hidden Rock Park (2014).
View of a sub-horizontal (nearly flat) part of the big outcrop at Hidden Rock Park. Hammer is ~40 cm in length.
A view to the south-southwest on the big outcrop at Hidden Rock Park (2013).
What are the prominent features that are well exposed here?
A view to the northeast on the big outcrop at Hidden Rock Park (2018).
Up-close with the bedrock at Hidden Rock Park (2019).
Standing tall at Hidden Rock Park (2005).
Hooray for the outcrop worksheets! Katie Valery at Hidden Rock Park (2016)
Post-geology playtime on the swings at Hidden Rock Park (2018).
Chow time at Hidden Rock Park (2019).
Feel free to answer some of the worksheet questions and join our class conversation. Comments from everybody out there in learning land are most welcome.
I’ll follow up with answers from our field observations in a few days and summarize what we have learned from the bedrock and structures at Hidden Rock Park. Then we’ll take that next step and relate our local observations to broader regional questions about the tectonic history of the Virginia Piedmont.
1 Here’s the roster of past blog posts about the Earth Structure & Dynamics field trip
2019- Neoacadian Poets in the Blue Ridge
2017- Explorations in Time-Depth Space: The Earth Structure & Dynamics Field Trip
2016- A Hard Freeze in the Basement: The Earth Structure & Dynamics Field Trip
2015- Over the Hills and Far Away: The Earth Structure & Dynamics Field Trip
2014- 50 Hours in the Field: The Earth Structure & Dynamics Field Trip
2012- A Mobile Mob: The Earth Structure & Dynamics Field Trip
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X are features called boudins!!! Also, the foliation appears to be folded in some of the images which is significant because it indicates some sort of deformation occured at this site. I’m very upset that all our field trips got canceled and hope to be able to visit this site one day in the future.
The rock appears to be gneissic with some boudins and folds present. I am sad that we did not get to go on the field trip this semester and that our practice in the field got cut short!
Some of the foliation seem to be folded which gives insight to its deformation. In the fourth picture after the worksheet, these folds seem to be nearly recumbent with an angular hinge and a tight interlimb angle. Additionally, the features at point X are known as boudins. The pictures for these past trips look great! I hope one day I can visit this outcrop.
There seems to be some folding on the foliation. That’s important from an educational perspective to help us remember the distinction between metamorphism and deformation. Both happened here but they are different. The foliation is a result of metamorphism, where the folding is deformation. Sad i missed seeing the boudins 🙁
Love the boudins, they’re one of my favorite geologic structures—so much so that I am tempted to call everything a boudin, even if it is most certainly not one. “Boudinage” is also just an excellent word. There is definitely some nifty folding happening in this foliation, so the rock has been deformed quite a bit. It would be wonderful to hold the “lovely” field worksheets once again and draw yet another beautiful strain ellipse, but alas. Hope everyone is doing well!
My preferred strain ratio estimate is 10.
As an ES&D alum, I found this field trip to not only be an epic bonding experience, but invaluable field practice. Applying classroom material in the field is incredibly difficult! Practicing these skills in the field, failing, and trying again is what makes geology glorious.
Great article.
Last year’s rock-forming minerals field trip included a stop at Hidden Rock Park and I remember hearing that I would be able to identify a lot of the structures in this outcrop when I took ES&D. It’s too bad our semester got cut short, but we’ve learned a lot: you can clearly see boudinage, folding, and foliation, something I couldn’t have told you much about last semester.
The rock seems to be gneiss，and it is folded. One of the pictures has shown a fold with angular hinges and tight interlimb angle. The X features are boudins.
The features that stand out to me in the pictures are boudins (as in point X), folds, and mineralized veins. Based on the pictures, you can see that the foliation is folded. And to answer the question if that is significant or not – yes! Folds occur in tectonically active settings which tells us that these rocks, now situated in a mostly non-tectonically active setting, were deformed by tectonic processes. This can give us information on the paleoseismology in the Blue Ridge and possibly tell us something about ancient orogenic events. Unfortunately, my class and I were not able to physically venture to these outcrops but I am hoping that one day soon, we can enjoy these trips together again.
The foliation in the rock does appear to be folded, which is significant because the orientation and extent of the folding can give insight into the kind of strain that the rock experienced. The features exposed at point X are boudins, which also indicate that the rock has been deformed. My preferred estimate for the bulk strain ratio is 2. While it’s disappointing that we aren’t able to go on the field trip this semester, I’m glad that we’re getting an opportunity to look at one of the places that we would have gone. I’m looking forward to future field trips once we are all able to return to campus.
Hi! I enjoyed coming to this park during the Minerals field trip last semester. Wish we could have gone as a class but I know there are many more geology adventures in our future.
I would like to estimate the bulk strain ratio as R(s)=2. Tried my best to plot the strain ellipse with North as the top of the page:
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Noooo my strain ellipse failed when I posted the comment (I had spaces in between each period) Maybe this will work:
…………..*…*…….
……..*………*…….
……*………..*…….
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…..*….*…………..
I feel as though picture 6 summarizes our semester as it displays what appears to be boudins, some folding, and foliation or perhaps lineation of the rock. It’s also pretty cool how the pictures show both boudins that have been completely separated in their final state and boudins that are pinched in the process of boudinage. Pretty unfortunate we had to be home instead of exploring the Appalachians.
Wow, now that is definitely NOT phyllite. Looks to me like folded gneiss with some pretty cool features. My preferred strain ratio depends on my mood, but today I’m feeling an R = 10. Not to mention how much this outcrop makes me appreciate feldspar!
What’s truly shocking is that no one has noticed the DEXTRAL shear that might even be, dare I say it, TRANSPRESSIVE?
In all seriousness, this is a great outcrop with lots of potential for learning. Where will the blog go next!
I’m going to estimate the bulk strain ratio is 4. I will also estimate that the strain ellipse is oriented with the x-axis in the NE direction and the z-axis in the SE direction. Great pictures!
Side note: Hidden Rock kind of sounds like hanging rock. If you haven’t seen the most recent version of “Picnic at Hanging Rock,” you should check it out. Now that’s one spooky field trip.
Wow so many familiar faces in these pictures 😀 ! Using the picture with the boudins and the 10cm pocket knife, I measured the strain ratio of the boudin in the bottom left corner of the picture to be about 2. The X-axis is 22cm and the Z-axis is 12cm, so the Rs is close to 2. I can’t draw a strain ellipse here, but the long axis has been tilted about 40 degrees east from originally 0 degrees. Using the longer boudin in the bottom right corner of the picture would give a wildly different strain ratio however.
That sub-horizontal outcrop (structures “x”) features some lovely boudinage! Since they’re featured in exposed bedrock, some uplift must have occurred to bring them to park-level. Evidence of tectonic activity abounds in Goochland!
Woohoo! Boudins and foliation galore! Using the 5(?ish?) picture with the 40 cm hammer I calculated an x axis of approx. 40 cm and y of approx. 15 cm leading to a strain ratio of 2.67, closest to the worksheet estimate R(s) = 2.
I would describe the strain ellipse as having an X axis 40 cm long tilted about 10 degrees east of north and a perpendicular Z axis 15 cm in length.
I tried to make a visual below, not sure if it worked:
|____,-”-,_|
|__/___/_|
|_/___/__|
|_’-,,-‘____|
Gil, I disagree with your assessment. I was there on a horse pulling a buggy full of samples with Anna Jonas many many years ago. I think The Tribe nailed this.
Woo! Boudins baby! At this point in the semester, I’d say we’re all boudinage masters. Looks like there are also some recumbent tight folds as well as mineralized veins. This bedrock must have undergone some crazy deformation as well as metamorphism!
I have to say I was fortunate enough to go to Hidden Rock Park for our Rock-Forming Minerals class with our famous petrologist, Doc Otis. In fact, I have a similar picture of that beautiful Z shape deformation of the granitic dike! I believe this is the Maiden’s Gneiss, which came from a protolith of a more mafic type granite (though it was mentioned it could have been sedimentary?). This gneiss contains minerals such as biotite quartz, and most importantly, feldspars. I was looking forward to getting some practice in dealing with orientations and measurements :(. The foliation does appear to be folded, though I would not say dramatically so. The features labeled X is, of course, boudins! Using the Z-shaped deformation, I would say the strain ellipse shape would have the x-axis pointing just slightly east of the north label. Super bummed we were not able to venture out and do fieldwork this semester. Thanks for the blog post!
The features at X are boudins in the Maiden’s Gneiss! I was lucky enough to visit Hidden Rock Park with my Rock Forming Minerals class and Doc Otis last semester. Back then I could really only tell you about the mineralogy of the rock, but thanks to Chuck and ES&D I can now recognize some structural features. The folding in the foliation indicates that this rock has experienced both metamorphism and deformation.
This outcrop seems to be gneissic rock, and I do see foliation that is folded here. The foliation is folded, which is significant because that indicates that there was a deformation event that had to have occurred at this site! The structures at X are boudins, which I love to see! If I had to estimate a bulk strain ratio, I would say probably Rs = 2. I really wanted to get more practice out in the field this semester as well, so I am very bummed, but I will say that I’m lucky to have a professor that is so dedicated to our learning and is putting in the effort to continue to teach us even with these challenges.
I am pretty sad our chance to explore the outdoors has been cut short, but luckily I had the lovely Doc Otis bring me to Hidden Rock Park in the fall. I do believe I see a folded fold which indicates that there was deformation that occurred after a separate deformation event! spectacular! But in the end, what troubles me the most is that we missed the opportunity to address what Gabe saw in those rocks that made him sweat so profusely. I know that as I’m sitting here thinking about it, I too have begun to sweat out of anticipation for the possibilities.
This trip really would have been a blast. The stoke factor peaks in the field, truly.
The outcrops at Hidden Rock Park appear to have folded rock, cross cut by a granitic dike, which was later tightly folded and boudinaged. The boudins present are of many different sizes. It is clear that there was definitely extensive deformation as well as metamorphism at this outcrop.
I’m sad we had to miss out on the opportunity to visit Hidden Rock Park this spring. However, I was lucky enough to get my hands dirty on the Gladstone field trip earlier this spring when the skies were still blue, having Venus blind us in the night sky was our only worry, and there was no stress.. – something the Hidden Rock Park trip seems to have plenty of!! The structures at point X are perfect examples of features that experienced stress: BOUDINS!! These boudins are the result of the stretching and deformation of the granitic dikes crosscutting the folded gneissic rock (foliation is visible as well). In the first picture after the worksheet, there seems to be some offset of the folded layers along the crosscutting dike: has faulting occurred at this site? Has the rock traveled from a tectonic active area? The questions..
The structures marked with X are boudins! I remember going on that field trip in Rock-Forming Minerals and being introduced to boudins, but having no idea how they were created. It’s pretty cool to be able to apply information from this class to answer questions about structures I was curious about in the past.
I really hope I get to see this park sometime in my future as a William and Mary geology student. The main bedrock seems to be metamorphic with igneous boudinage, indicating some form of intrusion taking place. It’s a cool opportunity to see so much bedrock exposed alongside soil topography, and might have some evidence of the interactions between structure and surface processes.
As some of my fellow classmates from last semesters Rock Forming Minerals course with Doc Otis, I was lucky enough to have already visited this bedrock outcrop. Of course, then I was employing a completely different skillet in mineral identification whereas in Chucks Structure class we actually think about how this structure came to be and deformed the way that it did. I’m not very good at the whole structure part but I can identify the X structures as boudins which were once one layer that was segmented into the sausage like structures they now resemble. And who knows, if Earth Structure 2021 visits this outcrop, maybe some of 2020s who were robbed from this might be allowed to tag along.
I remember going on the Minerals trip last semester and some students who had already taken Structure were showing everyone the boudins and I had no idea what they were talking about. Even though we couldn’t go this semester, it’s so cool to look at the pictures and recognize the features that I saw previously! Now instead of explaining the mineralogy, I can also talk about the foliation and boudinage seen at Hidden Rock Park.
SUPER bummed that we didn’t get to experience a field trip like this. Luckily I was able to go to Hidden Rock Park with Doc Otis in the fall! I remember it being super cool in person. The folding is my favorite part! Field tripping in cyberspace is a great replacement if we can’t field trip in real life 🙂
RIP structure field trip 2020 :(. I am thankful however that I was able to visit Hidden Rock Park for rock forming minerals with the one and only Doc Otis this past fall. And spoiler alert, the feature exposed at point x are what we call in the realm of geology, “boudins”. Boudins are magical in how they can be a dried cured sausage from France, however, in this case, we are referring to the “sausage-like” shape in the rock resulted by extension.