What formed this ancient, 24,000 foot tall underground rock structure? | Appalachian Geology
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- เผยแพร่เมื่อ 15 ต.ค. 2024
- This video talks about structural geology under northern Virginia in response to a viewer question. Even though the Appalachians aren't very high in northern Virginia, gigantic rock structures that remain almost entirely within the ground are still present. The very tops of these structures are exposed at the ground surface to create the landscape that defines life in the Shenandoah Valley and surrounding areas. You can learn to "see" underground geologic structure by looking at patterns on the land surface. This video uses block diagrams and Microsoft Paint sketches to illustrate Appalachian Geology in the mid-Atlantic. Even though the southern and northern Appalachians have higher and more rugged landscapes, mid-Atlantic structural masses are arguably bigger, even though their presence has to be visualized!
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"I'd be surprised if anybody is still watching."
*Raises hand. "Yes sir, I am here in the classroom."
This channel scratches an itch of discovery and investigation for me. The LIDAR discussion is always intriguing, and I am constantly wondering what kind of rocks I would see on the surface at a roadcut that would help me understand the deeper structures below. The diagrams you draw, well they drive home to me the realization that life is a thin film of grease riding on top of enormous forces. It is humbling. (Apologies for the multiple comments on this one.)
Comment til your heart's content friend! And thin film of grease is definitely the right visual. I will quote that in the Marianas Trench video
I’ve always been fascinated by the Appalachians, the Shenandoah area in particular and that meandering North Fork of the Shenandoah River. In fact an aerial and GPS quad of that area is on the inside cover of a Goode’s atlas that we had our house growing up, and I just bought a used copy. Cool stuff and thanks for the video!
Some of the best meanders around!
I really enjoyed getting my Geology degree at GMU (Fairfax, VA) and able to see all this in person. Thanks for posting another great video.
Your crappy Microsoft paint cross sections are great!
Keep em coming!
Thanks! They will definitely continue...
Don't know how I found your channel, but i grew up in the Appalachians in Northern WV and now i live at the base of the Rockies. Mountains and geology have always been a neat thing to learn about because of how incredible they can look. Your channel has helped me visualize how wild our planet is, especially the portions right in my backyard. Keep em coming!
it's an awesome region. glad you liked the vids
I love your videos! I have such a love of the geology of this part of the country and yet there are so few videos on it! Almost all USA geology videos are about out west
That is very true...I'm working to fix it!
Keep the Appalachian vids coming. I've seen so little on it and want to know more about where I live.
Gneissly done! I've driven through N. Va. and the Shenandoah Valley literally hundreds of times. I look forward to next time to observe the surface features with a slightly more educated perspective.
I'll check out your website, but I'm wondering what you have on where I live in western Pendleton County, WV. I look out the window at one of the many vertical crags of Tuscarora sandstone exposed in the gaps that drain Germany Valley into the North Fork River next to our house. I have a basic idea about these (and the cliffs of hoz. Tuscarora along the ridge of North Fork mtn. to the East) being remnants of the Wills Mountain anticline, but would love to learn more. A local favorite for geology field trips is along Nelson Gap Road north of Circleville, which includes the faulted Tuscarora forming the two parallel 'fins' of Nelson Rocks.
Hey man can you do a breakdown on the Jacksboro fault/ Pine Mountain/ Powell Valley/ Cumberland Gap area? Love your videos - thank you for your time!
Yeah I can do that. Might take a couple weeks, but I can get there. Jacksboro is pretty cool looking for sure!
@@TheGeoModels Awesome!!! Thanks so much I look forward to it.
Some super cool stuff
Martins Fork, White Rocks has soooo much going on. Definitely be stoked to see that,
@@robtaylor6638 yeah Pine Mtn is interesting. You run Martins Fork? Recall a crew being in there about 10 yr ago, maybe more.
@@TheGeoModelsThat was Tony and Eddlemon. Just recently finished scouting that mile of meat. Tough to get a crew for that stuff these days.
Theres a short vid on Vimeo from Kurts trip.
Thank you for producing this!
Enjoyed doing it
@@TheGeoModels I live on the Catoctin fm and have tried to determine the strike/dip of it locally for fun. It’s difficult given just how deformed it all is.
You’ve given me a great rundown of the region and I can’t thank you enough.
A bit northeast of there, they had to blast to install the sewer lines.
As far as I knew, we were on an intersection of limestone/shale down in the valley with more granite being seen out in the nearby mountains. Never found much quartz in the area, all the arrowheads you can eat though. Grandpa was sad that we didn't appear to have the gas type shale deposit.
I made it this far and I am still watching!
Well I like that! Appreciate it!
11:50 the illustrations at the top really show how the rock like snaps and stacks on top of itself. It's like if you took a bunch of ... DVD cases (sure why not) ... And set them all side by side in one layer. And then pushed on one end, and the other end was against a wall so it couldn't move. They would get tight, pressure would build, and eventually, a crack would be found and the DVD cases would start to pop up and stack
I lived just south of Strasburg (between Fishers' Hill and Maurertown) The pastures there are covered in sinkholes and caves. Families used to pick one and use it for the garbage and trash disposal. The surface limestone made it very difficult to put in fence lines.
I've seen a few of those sinkholes with a full junkyard in them! Might be some good antique bottles down in there somewhere...
Hey man, wonderful videos! And greetings from another Hokie! I was there for a couple of years in ‘73. Yeah, I’m old. I grew up in Bath County, VA, in a lovely region known as the Allegheny Highlands. We sort of backed up against Allegheny Front Range you talked about. A unique feature of that area was very little coal, but much geothermal activity. Beautiful, beautiful country.
Very cool! There will be a Seneca Rocks/Germany Valley video coming along one of these days. Thanks for the watch and comment!
I am watching it with great interest because I think the model will fit to explain some poorly exposed outcrops model in Central Sumatra Mountain, Indonesia. Many Thanks for your video.
Sounds interesting. The deep/blind duplex style seen in this part of the Appalachians is mostly a product of numerous thick shale horizons. The blue layer sequence is generally "strong" or more brittle, but it is bounded by a weak shale below, a very thick weak shale above, and another weak shale above the ridge-forming sandstone. So many shale horizons prevent large faults cutting the whole section. Some parts of the Canadian Rockies, like the Sukunka River section in British Columbia, show a similar style.
There’s a shale wall exposed near Shippensburg, PA, which is about 30 or so miles north of Hagerstown. It’s all fractured like you mentioned in this video.
Wow, so glad I discovered your channel! Could you please do a video about Raccoon Creek that runs south from mid-Ohio through Rio Grande and Gallipolis to the Ohio river? Specifically the geology of the area and how it affected the formation of Raccoon Creek? Love your maps and drawings! Thanks!
I definitely enjoy watching the paint models, and the LIDAR images, and I understand the value of the skill you're demonstrating to people who are becoming geologists, but at the same time I miss the old sand/various other media physical models in the table that could physically crunch layers together or pull them apart. Watching it happen gave a context that seems difficult to reproduce in still images. Still love the channel, Cheers!
They'll be back...though not necessarily with the glass sidewall. More geometries are possible with a "3-D" cake of sand on a table top. But the point is well taken. Some will start to show up again directly.
@@TheGeoModels I can appreciate how much more time-intensive the physical models must be to, so I _really_ appreciate the time and effort! Thanks!
@@thirstfast1025 the sidewall models are so good for visualization, but I genuinely don't think they'll ever make the variety of structures you can get with the "cake" setup. There will always be drag against the sidewalls, and it sort of messes up the stress field. I'm trying to figure out to weave some of the cake-style models into these vids. Going to try one for Glacier National Park and Pennsylvania. Def got a good one for Jamaica as well.
@@TheGeoModels Can't wait to see the results! Cheers!
9:30 Those meanders are nuts!
About 31:00 So I was on a tour bus from Bath to Edinburgh (UK) one time and it seemed like an endless repeating cycle of ridge and long valley, ridge and a long valley. Is this a similar formation mechanism?
So down around Bath, the Mendips area is indeed a fold-thrust belt feature and is comparable to this in many ways. I think that's the closest thing in the UK in terms of fold-thrust belt structure and associated topography. Just how much the structure sets topography, though, I can't say. IGetting up in northern UK there are other landscape controls, for sure.
What is under NC Piedmont / WHERE DID THIS HATEFUL CLAY COME FROM? Also I heard there is unusually old surface bedrock. Thanks!! (I am Wake Co)
Thank you for sharing.
Glad to do it!
Fascinating seeing the folding patterns I wasn't familiar with the exact folding structures of the blue ridge but I know the area as I went to JMU in Harrisonburg for undergrad. I know a bit more of the geology towards the east of the Blue ridge where you have the Triassic basin, Piedmont and Costal plain regions which represent graben horst terrains from in essence the break up of Pangaea that didn't ultimately become the ocean basin. I personally live in the Piedmont with the local soil derived from underlying mica schist bedrock. (I always forget which kind of mica is biotite or muscovite). As the ancient horst everything is eroded down to the metamorphic and igneous/meta-igneous basement rocks.
The LIDAR stuff is interesting and I wonder how well it works with the other much deeper fascinating internal structure visualization mechanism seismic tomography and the vastly deeper structures that make these apparently thick to us layers of lithosphere look like a paper thin film in comparison. There is apparently a deep vast slab wall down in the lower mantle beneath the east coast corresponding to ancient subduction likely in Triassic timeframes. Its still slowly sinking its way down to the core mantle boundary amazing stuff.
Can you do a report on the region at New Martinsville West Va? The surface is one of the places the early Ohio River broke through the hills to form todays river bed, the northern region had glacial lakes that formed interesting benches, locally known at flats. And the Rome Trough and the Utica/Marcellus/Tulley shale formations lie beneath. I have a small oil and gas well in the Big Injun sandformation here. Any information is greatly appreciated!
So I had an Ohio River thing cued up for down the road. Might be a bit downstream, but a similar vein I think. Anybody in the greater Mothman corridor would connect to it. You can tell me what you think when it show up! Might get into a "what's under the plateau" thing too. You leasing your property for that well?
Kind of out of your area but would love to know whats under northern and southern Maine
That section of the North Fork Shenandoah River? About 14 miles in a straight line or about 44 miles in a canoe!
In the Sections 1, 2 and 3, what would the time frame have been to stack those sections up? There doesn't seem to be much if any erosion at the top of each broken section before it rode up on the one before it.
"A long time," for sure. I guess if you take centimeter per year of plate movement and need a couple kilometers of rock movement, your looking at several hundred thousand years minimum. I would imagine a few of the repeated blue structures were active at once, but the overall effect is a millions of years (probly 10's of) assembly, for sure. Erosion is an interesting point. There were thousands of feet more rock on top of this when it was fully assembled--the little scraps of youngest green were very thick and would have roofed the whole thing. The overall style of the structure suggest this thrust belt was not eroded much while it was forming, and what erosion did occur would have been widespread across the green "lid." The blue structures were "blind" during the process, lifting the overlying stuff to subject it to erosion. The southern example, with the big, long thrust sheets, likely recevied more erosion while forming.
That layer of Quartizite... Is it normal for that layer to be undisturbed, distinctive in that way from the layers above it?
Yes...the red layer is a weak shale...it's sort of like "grease" that allows everything above it to slide smoothly with disturbing what's underneath. It's called a "basal detachment" or "decollement."
Normal at least in a thin-skin fold and thrust belt like this one, I should say.
@@TheGeoModels Thank you very much for responding. I'm always eager to learn from people who know more than me, which, in this subject, is just about anyone, haha! Seriously though, it's appreciated. Thank you.
Awesome thank you
Glad you liked it!
Seeing all those folds in the crust makes me wonder;
Geology tells us that early Earth was much more volcano happy than it is today, has the crust perhaps been 'work hardened' by the added material and mechanical stresses, thus leading to a crust that is more resistant to holes?
Is there a reason the imbrication seems to be fairly consistent in block size?
Well, first and foremost that's what the seismic apparently showed, and that's what surface geo suggests...there aren't really any big structural highs or lows along this section, though there is some increased structural relief in the orange and light-colored sandstone nearby. It's a good question--most folks that have interpreted around here show it, and I think what information you can get from surface outcrop supports it. In the bigger, fold-thrust belt mechanics picture, I would say it implies a generally "stable" wedge top, without too much localized piggyback sedimentation or extreme localized erosion while folding/thrusting was going on. If I were to try to make it in a sandbox model, which can be done with reasonable success, you'd want fairly low basal friction, consistent thickness in the deeper (blue) layer, and a thick uppermost horizon that tapers towards the foreland. The key to the whole thing is having plenty of shale above the imbricating section to keep it cut off from what's going on above it. I think it's an awesome structural style. The Sukunka River section in the Canadian Rockies is similar, but not as fluid and "rolling."
Have you found evidence of Ice Age flooding in the Appalachians? And how about those boulder fields?
Ice Age river stuff is upcoming, for sure! This area doesn't show it, but areas west are basically as you see them today due to Ice Age drainage reorganization. The boulder fields are a wild thing, and obviously say something about climate. Got to be near 4,000 ft to see one in southwest Virginia, only about 2,000 ft where this video discusses, and only about 1,000 or so in Pennsylvania. They form well in quartzites and sandstones, but I've yet to hear a definitive opinion on what moved them (presumably freeze-thaw or something like that). Might do a quick video at some point on what you can see in lidar...there are obvious Ice Age freeze -thaw features in Pennsylvania that Google Maps actually captures.
Those incredibly regular meanders! What geological 'harmonic' has guided that development? There must be more of a story - this retired geologist is really intrigued.
They're pretty cool, and I'm actually not aware of any quite so dramatically expressed elsewhere. Part of it is the Martinsburg Shale substrate, and there is a strong fracture or joint set that allows the longer "limbs" of the meanders to be perfectly parallel. The fracture set controls all sorts of topography around there, and the meanders go wild in it. In terms of the density of meanders in an entrenched bedrock stream, I dunno bout that one! Glad you enjoyed it!
@@TheGeoModels The late Bob Young (Dr. Robert S Young), or "Doc" Young, as he was known to my generation of young geologists under his employ who were simultaneously in awe of and terrified by him, partnered with USGS geomorphologist John Hack on a short but fascinating USGS Professional Paper (PP 354-A, 1959) on the intrenched meanders of the North Fork of the Shenandoah River.
There are probably some at VDMR who remember Bob Young and his Charlottesville consulting firm, North American Exploration, Inc. NAE was my first employer out of Appalachian State's Geology Dept, where Va Tech's own Fred Webb was our department Chair throughout my undergrad career. I also spent a summer under the employ of Furman University on the NURE sampling program, directed by Ken Sargent (sp?). Small world.
I'm much enjoying your TH-cam videos and have relayed same to some of my increasingly elderly ASU classmates, most now retired from exploration careers.
28:30 still watching - some of us have staying power
What you called Gaithersburg is actually Frederick. Germantown/Gaithersburg is just on the right edge of the map.
Thanks! Glad it was worth watching close!
I've been eating up this content after discovering your Carolina Bays video. Geology has always interested me, particularly Appalachian geology.
Stonewall Jackson's stomping ground.
God
Water made it....