March 8, 2022
Lidar reveals geologic details of the “worst” coal mine in the Valley of Virginia
Posted by Philip Prince
By Philip S. Prince
At first glance, the Altoona Coal Mine of Pulaski County, Virginia, seems to be in just the right place. Coal beds in its Little Walker Mountain setting occur just up-section and downhill of a prominent sandstone bed, which forms an obvious “rib” on the slopes of the mountain. The mine was opened right at the base of this rib. This must have appeared to be a great location, as it took advantage of a stream valley to ease construction of a tram railway to the mine. Prospect pits and mine adits leading up to the Altoona’s location are visible in the GIF below. The rib is marked with a pink overlay, with mine workings visible as tiny dots to its right; the image that follows the GIF is a detail of mine workings adjacent to the rib.
Despite its apparently good location, all was not well at the Altoona Mine. Coal seams in the mine were too distorted and mixed with surrounding rock to be easily extracted, leading to its ultimate failure. Early 20th century geologist Marius Campbell addresses this issue at length in the 1925 report The Valley Coal Fields of Virginia, twice calling Altoona’s location “the worst” in the general area and the obvious reason for the mine’s closure.
Campbell connected the geologic issues in the mine with its position near a complex ridge pattern that implied large-scale folding in the underlying strata. His focus was on the apparent convergence of Little Walker Mountain and Tract Mountain southwest of the mine’s location. This pattern is visible in Google Earth satellite imagery, and is also quite noticeable from ground level near the mine. Little Walker Mountain, which is typically an arrow-straight ridge, is noticeably buckled in the vicinity of the mine, and Campbell may have seen this feature as evidence of rock deformation associated with the Little Walker-Tract Mountain structural setting.
Campbell was definitely onto something, and he was certainly correct that weak rocks, like coal, focus deformation when surrounded by stronger material like sandstone or limestone. He attributed rock distortion at the mine to “cross-folding,” which appears to be his term for the structures that create the locally buckled appearance of Little Walker Mountain. As it turns out, Campbell wasn’t exactly correct, but accurate interpretation of the area is essentially impossible from field data alone due to limited outcrop. Additionally, no high-altitude imagery was available at the time, preventing Campbell from having a Google Earth-style, satellite-level view of the mine’s setting. Today, lidar-derived imagery quickly reveals the true structural issue at the mine, along with the large-scale context of the distorted coal beds.
A close look at a 1-meter lidar hillshade image reveals that the Altoona Mine is indeed positioned exactly in a fold hinge. This fold structure is more significant and affects a greater thickness of rocks than Campbell’s “cross fold” concept suggested (more on this below), but it is still subtly expressed, even in the high-resolution lidar imagery. The GIF below overlays color bands onto distinct rock units to highlight the fold, which is very tight and probably faulted. I think the fold is most visible just below and left of center, where the purple and blue bands meet in a V-shaped point. From here, the faint layer patterns can be followed towards the mine. Layers young towards the right; purple covers Devonian-aged rocks, while the mine is developed into Lower Mississippian-aged rocks.
The significant folding near and left of image center appears to die out in the vicinity of the mine, where the sandstone rib that highlights the coal location does not immediately appear offset. An even closer look suggests that the rib is deflected to the observer’s left, indicating that the rib layer and coal-bearing interval are either folded into a very tight syncline or repeated by a minor thrust fault. The mine is located nearly atop this highly distorted area, which nicely explains the messy condition of its coal beds.
Based on these lidar-derived images and my own experience in the area, the structure immediately adjacent to the mine would not be decipherable through field work. Sedimentary rock layers visible in the lidar imagery do not actually produce much surface outcrop; they only create faint bulges on the land surface that require a 1-meter resolution (or better) digital elevation model to see. The fine structural details at the mine are still not completely clear in the imagery, but I would offer the two conceptual models below as explanations of the folding and faulting that produces the observed surface pattern. They are very similar (differing only in terms of a small fault vs. a fold in the mine area), and both would produce considerable distortion of the coal-bearing horizons. The models use a wedge-type geometry instead of a single fault cutting all the way through the affected section. This is a way of reducing apparent offset of the pink sandstone marker bed, which is not obviously deflected to a ground observer or coarse-resolution map user.
Both models focus shortening into the coal zone and would result in thickened, duplexed coal seams. Thickening of coal beds is one of the details reported by Campbell, with the main coal bed in the mine reaching 125 feet (~38 meters) thick in some areas despite an average thickness of 7 feet (just over 2 meters).
In addition to locally thickening the coal, the tightness of small scale folding in the mine, along with possible faulting, would have broken surrounding sandstone layers and forced pods of sandstone into the more ductile coal. Coal beds in the mine would thus have been observed to be locally atypically thick or atypically thin, and full of fragments of surrounding non-coal rock. As a result, the mine would have been nearly impossible to develop efficiently.
As mentioned earlier, folding around the Altoona mine is not the result of the mine being between Little Walker and Tract Mountains. In actuality, the fold on which the mine is situated has developed along one of at least two thrust fault structures that climb out of the Devonian-aged rocks into the coal-bearing Mississippian aged rocks at the mine. These faults produce the bends or buckles in the Little Walker Mountain ridge and may have accommodated displacement as bedding plane faults in the Mississippian strata, either in the coals themselves or in the overlying Macrady shale. I highly doubt these larger faults would be easily field-mapped either, due to the difficulty of finding meaningful bedrock outcrop where the faults climb upward into the Mississippian layers. Where the faults are operating as detachments or flats within a single stratigraphic interval, they are not readily identifiable even when outcrop is present. The GIF below traces these faults relative to the mine’s location.
While coal extraction was not particularly successful at the Altoona Mine (and never will be!), the mine’s coal issues highlight a structural scenario that is valuable to structural interpretations of the surrounding areas. Cove and Tract Mountains, the respective left and right elliptical ridges south of the mine, are part of a large structural mass that is difficult to relate to neighboring thrust sheets. Cove and Tract Mountain (as well as Draper Mountain to the south) reached their structural position on what should have been a high-displacement thrust fault, but evidence suggesting this high displacement is hard to find.
Activity on the detachment fault that terminates around the Altoona Mine could help explain some of the “missing” fault displacement, particularly where the additional fault to its north is considered. These otherwise subtle features would largely escape consideration were they not connected to a conspicuously bad coal mine, making the Altoona a geological success long after its closure!
Philip Prince is a Project Geologist with Appalachian Landslide Consultants, PLLC, in Asheville, North Carolina. He also conducts geologic mapping in the Virginia Valley and Ridge for the Virginia Department of Mines, Minerals, and Energy. More posts related to his field experiences and remote sensing work can be found at princegeology.com.
Excellent analysis. Helps me to understand why the Altoona Mine failed so quickly (gone by 1900) and also why the backers of the Empire Mine failed to raise investment funds despite their ambitious construction program and ready customer on hand. Their 1923 prospectus complete with previous production numbers and photos of the existing operations make an interesting read. Copy not available on-line unfortunately. Ratcliffe Museum in Pulaski has a copy.
All of the Brush Mtn, Little Walker Mountain, and Pulaski coals are in a tough spot, geologically speaking…it’s surprising that they aren’t more deformed and unworkable. I’m about to be working on the ground in the Gunton Park area and hope I can come across some of the old prospects that never panned out. The coal-rocks on Little Walker are quite different from the “same” rocks on Tract Mountain, even though they are the same age and physically close to each other. They are almost certainly separated by a significant thrust fault that is just hard to see in the landscape. I hope to do a write-up about it here in a few weeks using some more lidar imagery. It’s been a great experience to be on the ground in this area, as I never spent much time in Pulaski or Wythe when I was teaching at VT. Thanks for reading!
Outstanding ! THANK YOU for this piece of work ! My family has lived in Patrick, Floyd, Roanoke, Montgomery and Pulaski Counties for almost 250 years. So I am always interested in the geology, history, economics, sociology &c of the area. I heard of the Altoona Mine thirty years ago, but never knew the location or the particulars. THANK YOU for filling in this gap for me.
Glad you enjoyed it! It’s a fascinating story. Everything looks different with the lidar imagery, for sure.
Hi I live off Robinson track Rd in Pulaski County I was told there were mines on my property Sure would like to know Cox Hollow rd Thank you
The biggest mine workings are north of the very end of Cox Hollow Road, where it turns to dirt and pretty quickly fords Tract Fork. There should be several obvious pits/collapsed shafts in the woods. I am not aware of any mining on the south (Tract Mountain) side of the road. Generally, the rock on the Tract Mountain side has less workable coal resources (and locally none at all) compared to the Little Walker Mountain side. The mine workings north of the end of Cox Hollow Road are not terribly far up in the woods, and they are the most southwestern mines on Little Walker Mountain.
I will email you at the address linked to your comment and send a map along.
Thanks for reading!
i live almost at the end of mines rd. the cemetary and (whats left of the) foundation to the church of the altoona/empire mines is in my back yard. the church foundation is no bigger than a small room. its mostly a square cutout in the ground now. there used to be a small pot belly stove there and there still may be a few hand made bricks left that are stamped “EMPIRE”.
growing up we found plenty of piles of slag and caved in shafts, as well as a few that have recently collapsed that were relatively close to the surface. my brother and i also found what we believe to be a ventilation shaft on the side of the road on Langhorne Rd. we quickly gave up checking it out once we were surrounded by an extremely upset nest of yellow jackets.
I live at the end of cox hollow rd. In pulaski co.l am a cox that was born and raised in coxs hollow ,my father also. Growing up i have always wondered when those mines were active or if they were.my father new very little about them himself he was born in 1930,i was born in 1957.i surely appreciate you shining a lot of light on this,i have really learned a lot here in a few minutes that i have wandered about all my life. Thanks again. Freddie cox
I left a comment yesterday 2 28 2023,I don’t know how long it takes to go through. But I hope u can reply when you get time thanks Freddie cox