Geology of the Mount Rogers Formation and Virginia Creeper Trail

Mckenna here- This post will show you the geology of the Mount Rogers Formation and Virginia Creeper Trail on a recent field trip I took to Virginia!

Day 1

Image 1. Our professor leading us to a geology lookout point on the way to Abingdon to see an outcrop (visible rock formation).

On October 10th of 2019, my Mineralogy, Petrology, and Geochemistry class went on a 4 day field trip to Abingdon, Virginia. Imagine this: it’s October. You love fall but you’ve lived in Florida your whole life, and you finally get to wear all the winter clothes you bought for no apparent reason. Considering these facts, my excitement for the trip was through the roof. After a 14 hour ride in a van with 10 other people and frequent restroom stops (much to the dismay of my professor) we finally arrived in Abingdon, Virginia to the joys of leaves turning colors and a crisp feeling in the air. A van full of (mostly) Florida-born students  seeing fall leaves for what was probably the first time was a van full of amazement and pure excitement. It sounds silly, but it was really wholesome seeing how giddy everyone got just by seeing some colorful trees (me included). We got to our hotel and prepared for the next day spent in the field. 

Day 2

Image 2. Rhyolite at Mt. Rogers with visible high silica flow banding (lava flow)

We woke up early in the morning and were able to enjoy a delightful breakfast made by the hotel to kick start our day. I packed my lunch and snacks and put on layers of clothes to be ready for any weather. I put on my new wool socks from the outlet store and old hiking boots that seemed structurally sound at the time (important to note for later). On our way to Mount Rogers in Damascus, Virginia we happened to take a road conveniently coined “The Twist”. As a long term participant in unwillingly becoming motion sick in situations such as going down one of the curviest roads in Virginia, I wasn’t thrilled. Luckily, I knew mountain roads could be bad so I packed some Dramamine which I made sure I took every time we got in the van from then on. 

Once we got to Mount Rogers my friend and I immediately had to use the bathroom which in this case, was wherever you felt like the trees concealed you enough. They don’t really mention this too much for field trips/field camps but bring toilet paper!! It will make your life a lot easier. After this venture, we were soon on the hunt for rhyolite. Rhyolite is a type of rock that my professor has talked a lot about and I had heard from other students that it is mostly what you will be seeing on the Virginia trip. It is a type of igneous rock that has a very high silica content so it is considered felsic (which is usually light colored). Rhyolite is made up of the minerals quartz, and plagioclase with smaller amounts of hornblende and biotite

The upper part of the Mount Rogers Formation consists mostly of rhyolite which we have, thanks to the continental rifting that occurred around 750 mya. The volcanoes that were once present here erupted and the igneous rock formed from the lava flow. 

Figure 1. Formation of rift valley in Mt. Rogers (From Radford)

We used our rock hammers that you can see in Image 2 to break off bits of Rhyolite and observe them under our handheld lenses. Through these lenses, we could (almost) easily identify the minerals present in our rock samples. 

Stop after stop, we observed more rhyolite. It became quite easy to answer our professor’s questions as to what type of rock we were looking at; the answer was usually “Whitetop Rhyolite”. There were, however, different types of rocks as we descended down the side of the mountain: buzzard rock and cranberry gneiss.

Image 3. Buzzard rock
Image 4. Cranberry gneiss

 

 

 

 

 

 

 

 

After we were finished at our first destination, we drove off to Grayson Highlands State Park. Here we observed more outcrops of rhyolite with a new fun bonus: tiny horses. Apparently, these tiny horses were let loose here in the late 20th century to control the growth of brush in the park. Now, there are around 150 of them that live in the park and are considered wild. While the park discourages petting the horse, you are able to get a cool selfie with them!

Image 5. Selfie with tiny horse in Grayson Highlands State Park

At the state park , there were lots and lots of giant rocks to climb on which everyone seemed to enjoy doing. So, while climbing the rocks, we were also observing and identifying them so it was a great combination. I was taking the liberty to climb almost every rock I saw and everything was going great for the time being. At one rock, I decided I wanted some pictures, for the memories! Mid mini photo shoot, I realized that the sole of my hiking boot had come clean off. Luckily, TWO very prepared people in my class happened to have waterproof adhesive tape and offered for me to use it to fix my boots. I was so thankful (and impressed that they had it in the first place) for the tape and used it to wrap my sole back to my boot and reinforce my second one because I noticed that the sole was starting to come off. The taped boots almost got me through to the end of the second day but I had to do some careful, soleless walking to get back to the van. I was able to go to the store near our hotel to get some replacement boots for the third, and final day in the field. 

Image 6. Realization of broken boot
Image 7. The final product of taped boots

Day 3

Image 8. Shale sample taken from outcrop along the Virginia Creeper Trail

The last day in the field was spent at the Virginia Creeper Trail in Damascus, Virginia. This specific trail serves almost entirely as a 34 mile cycling trail; by almost entirely, I mean entirely a cycling trail with the exception of a class full of geology students. Our day consisted of identifying rock types in outcrops along the trail and receiving a wide range of looks from cyclists passing by as our lookouts at the front and back yelled out for us to get out of the way. We walked around 1.5 miles of the trail, all while taking notes and pictures while our professor and teaching assistants were explaining each outcrop. Once we reached a certain point, our professor informed us that they would be leaving to get the vans and we would be walking back the way we came plus a half mile or so and identifying each outcrop while counting our steps and noting our bearings. So we measured our strides and got into groups to commence the journey. The goal of this was to eventually be able to create a map of our own that indicated each outcrop type and where they were on the path we took. 

Image 9. Mudstone displaying “varves”, which are a seasonal bedding pattern that develops in high latitude lakes. The thicker deposits develop in the summer and the thinner ones develop in the winter (please ignore my nailpolish-it is not a good idea to paint your nails before a geology trip).

This all sounds relatively simple, right? The answer is well, not really. The entire venture took around 4 or 5 hours and honestly made some people a little grumpy. I was happy though, because among the rhyolites and basalts, we were also able to see some really cool sedimentary rocks. Along the way we saw some awesome shale (Image 8) which we were told had some fossils in it if you looked hard enough. Of course, being interested in sedimentary geology I would’ve stayed forever chipping away at the shale to find a fossil but we were quickly ushered along by one of our professors. Shale is a type of sedimentary rock that is formed from packed silt or clay and easily separates into sheets. This type of rock is formed under gentle pressure and heat which allows organic material to be preserved easier as opposed to igneous or metamorphic rocks. As we continued along the trail we also saw mudstones and sandstones, diamictites, and conglomerates. After reaching the end of our journey, my group might have gone a little overboard and recorded 51 different outcrops. The outcrops we recorded could be reduced to: basalt, rhyolite, diamictite, conglomerate, sandstone/mudstone, and shale. The last field day was now concluded with tired feet but happy hearts as we listened to Fleetwood Mac in the van on the way back to the hotel.

Image 10. Diamictite (type of conglomerate) with poorly sorted grains suspended in a clay matrix. This specific rock was likely created by glacial activity and/or volcanic activity.

Day 4

We had a very early morning, skipped the hotel breakfast (they put out fruit and pastries for us though), and piled into the vans for a long journey back to Tampa, Florida. This trip was everything I had hoped it would be and made me fall in love with geology even more than I already was! I hope to go on many more adventures like this in the future. 

Bonus images of cool finds:

Image 11. Swallowtail feldspar (basalt) contains epidote and quartz. Lava cooled very quickly which caused rapid crystallization
Image 12. Rhyolite with pyrite (fool’s gold) clasts visible under hand lens
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