Cave opening in McConnels Mill, PA. Photo by Rivadiva.vila, Wikimedia Commons
(Click on the following link to lsten to an audio version of this blog …. A cave in Pennsylvania
(This essay was originally part of my now defunct Between Stones and Trees website)
Western Pennsylvania has many caves. Some of the caves are small, scarcely more than cracks that run through layers of bedrock. Other caves, though, are massive systems of vast, interconnecting tunnels that cut through hundreds or even thousands of feet of rock.
Caves form in limestone. Limestone is a sedimentary rock made from calcium carbonate materials that originate in the shells and cellular encasements of living organisms that live in the ocean. The small rectangular area on the North American plate that would become Pennsylvania was a tropical sea bed for many millions of years. Corals, shelled mollusks, algae and single celled foraminifera thrived in its warm, shallow waters and vigorously accumulated and deposited vast amounts of calcium carbonate into the growing layer of sediments. These calcium carbonates with varying amounts of added sands and other mineral separates fused together in the hot layers of forming rock that were steadily squeezed by their own accumulating masses. Over millions of years of time layer upon layer of limestone, sandstone, shale, and siltstone formed (Barnes and Sevon 2002). The thickness of each layer was a function of the time and rate of sedimentation, and the exact nature of the rock was determined by the predominant make up of the sediments themselves.
Water passing through the atmosphere picks up carbon dioxide and forms a very weak carbonic acid solution. If this carbonic acid seeps through limestone it will dissolve away the calcium and form infiltration passageways that can, over very long periods of time, grow into caves. If the limestone is very rich in calcium, wide passageways can form along with dripping accumulations of the calcium-rich waters that grow into stalactites and stalagmites. If the limestone is richer in sands than calcium (a “siliceous limestone”) then often only the calcium is removed by the acidic water and the formed potential passageway is left filled with loose sand. For this type of limestone to form a cave, then, a very substantial flow of water is required to erode away the un- cemented sand particles. The location of the limestone, the size and composition of its deposit, and the amount and directionality of the entering water, all will contribute to the eventual structure and shape of the cave (Cale 1983).
Chestnut Ridge. Photo by N. Tonelli, Wikimedia Commons
In southwestern Pennsylvania, underneath the Chestnut Ridge and its thousands of feet of sedimentary rocks, are great, isolated plates of sand-rich limestone called Loyalhanna Limestone. These limestone plates, like all of the sedimentary rock layers of the ridge and plateau beyond, have been folded into crests (“anticlines”) and troughs (“synclines”) by the same forces that drove the formation of the ancient mountains from which the sands, silts, and clays of the sedimentary rocks themselves were formed. The Taconic Mountains (440 million years ago), the Arcadian Mountains (350 million years ago), and the Allegheny Mountains (260 million years ago) (which have split and eroded down into our present day Appalachians) all have contributed to the sedimentary rocks of Western Pennsylvania and to their distinctive tilted orientations (Van Diver 1990).
One of these Loyalhanna Limestone sections is located on the western slope of Chestnut Ridge about ten miles south of present day Uniontown, PA. This section of limestone is fifty feet thick , two miles long, and one mile wide. It is approximately 450 feet below the soil surface and is angled at a downward running slope. The acidic rain water entering the top of this great plate of siliceous limestone has been slowly eroding away its calcium and some of its sand for millions of years and has left behind a partially sand filled cave system of great complexity and size. This cave system is Laurel Caverns, the longest cave in Pennsylvania (Cale 1983).
Photo by daveynin, Flickr
A hike through the passageways of Laurel Caverns is a hike (and crawl) through the solidified sediments of an ancient ocean basin. Moving through this cave is like slipping through a layer of ancient time with the mass of its past below you and the weight of its future above. In 2006, Deborah, Marian, Joe and I had the opportunity to hike through the deep parts this cave and experience its incredibly complex structure.
It would be very hard to report a blow by blow, room by room, rock-fall by rock-fall account of our climb through the cave. I was not able to take notes on the hike because my hands were nearly as active as my feet in the long descent and then ascent through the cavern.
We spent three and a half hours in the cave. The interconnecting tunnels we moved through felt endless, and our initial downward path felt as though we were going to enter the very bowels of the Earth itself. But, eventually, we came to a narrow space and a solid rock wall under which the cave stream flowed on its path to eventually emerge out through the side of the ridge. I can, though, even without specific notes, pull back many of my impressions and ideas.
Photo by D. Fulmer, Wikimedia Commons
First of all, I was worried about being in the confined space of a cave. I was worried about the possibility of claustrophobia. Confined spaces and crowded places on the surface have always made me very uncomfortable. I was also worried that someone who was six foot four and two hundred and fifty pounds (i.e. “me”!) might get stuck in some of the “normally” sized squeeze holes between the cavern sections. It turned out that none of these worries were significant. There were some tight places but none were impossible especially after I was well lubricated with sweat and pounds of loose sand.
The feel and the smell and the sound and the touch of the cave:
The feel of walking along in the absolute darkness with only the light of your flashlight to guide you is not unlike being out at night walking a trail by flashlight. You don’t really notice the mass of rock just above your head or just off your shoulders until you slam your helmeted head against it (and this happens very regularly. It’s incredibly obvious why helmets are required for caving!). You don’t really notice that there is no breeze and no sounds of insects or other animals. It was like being out in the darkest, stillest night and only seeing what you shine your light directly on.
Photo by D. Fulmer, Wikimedia Commons
I never experienced any feelings of claustrophobia or confinement on this subterranean hike, but if the tunnels had been lit, I think that the sense of confinement might have been overwhelming. We would then have been able to see the narrow dimensions of the passageways and the closeness of the rock above us. If we had had any broad perspective at all we would have felt the weight and confinement of all of the surrounding rock.
The cave smelled cool and wet and full of simple, clay-rich scents. Not a soil smell at all (soil smells of biological compounds and past events, a cave smells like wet rocks).
Marian and Joe with stalactite.
The sounds in cave were also mostly caused by water. Water was steadily trickling, and dripping, running, and gurgling. Water made the cave (and is still making the cave). The tiny streams of gathering water form up into narrow, fast running rivulets that eventually make the three, narrow “streams” that run quickly though the volume of the cave. The fast running water, though, erodes away the carbonates and sands imperceptibly slowly.
The sounds of water lead you through the passageways. Your touch the walls as you walk. You are instructed to use three points of contact at all times (except when you have to jump from rock to rock or swing from handhold to handhold), so your fingers get a continuous feel of cave. The coarse textures of the sand-rich limestone, the crumbling of the decaying, “rotten” rock that has lost its calcium” glue”, the slippery smoothness of the wet silts and clays accumulating in the puddles of the rock concavities all passed over our finger tips (and down our backs and over our clothes and onto our faces!).
So the cave is water in sound and smell. It is walking alone while concentrating on a 4 inch diameter lighted disc. It is the feel of sands, and silts, and clays. It is the coolness of a deep basement far below the weather and the activities of the house.
Photo by Sir Joseph. Wikimedia Commons
I felt like a rock-eating worm digging my way through the geological layers. We did a lot of the hike walking upright in fairly large tunnels but also frequently had to squeeze ourselves though holes and tubes and push ourselves up and around narrow separations of rock. These spaces gave me the distinct sensation of being legless. Many times I used my elbows to climb up a rock chimney (my forearms and elbows are well scrapped and abraded from the use). Many times I twisted my torso and stretched an arm up and over my head to grab a handhold to pull myself along through a space in which I could not use my legs (only my toes).
We slid ourselves along the rocks. We gathered up pounds of the rocky debris on our clothes and boots and hands and faces (the before and after pictures were amazing!). Compared to the “civilized” caves I had visited in the past in which you are repeatedly told not to touch the rocks or the cave walls, this was an emersion in the extreme “caveness” of the place. The cave grew fractions of millimeters larger from our passing. Parts of the cave traveled to our car and then to the pizza place where we grabbed some food after the hike. Our laundry baskets and our washing machine filled with pieces of the cave, and then these drained out in the wash water on an extended rock cycle of change.
A few vivid places in the cave:
We were in a narrow tunnel on our decent. This section of the tunnel, though, angled upward at about 45 degrees. Halfway along, a large, flat, slab-like rock blocked the passageway. The rock was about 6 to 7 feet wide and about as high and was very smooth. Our guide (Bernie) said that this was our first challenge. You had to stand up to the rock with you right foot on a narrow ledge, push upward, and grab onto the upper edge of the rock. Then, you had to pull yourself up and over the rock and drop down to the next part of the path. The upper rock edge was very sandy and felt (I could reach up to it with my fingertips before I jumped) too blunt and cheesy to hold on to. So, it was quite hard to leap off of the solid foot hold, and then grab onto a uncertain handhold, all the while sliding (probably) down a smooth rock surface into a deep (I think ….it was quite dark!) hole! Marian and Joe leaped off, grabbed on, and swung over the top right behind Bernie. Deborah was too short to catch the top so I had to give her a push up and over. I rocked back and forth for what felt like quite a while and then jumped and pulled myself over the top (in a slow press rather than in a cling and jerk). Good challenge! I almost didn’t make it!
Photo by Fulmer, Wikimedia Commons
A second memorable point was shortly after the leap over the smooth rock. This was the very long down slide that put us back on a downward trajectory of our descent into the cave. We came to a jumbled mass of rocks and climbed into a notch on the left-hand side. You had to swing your legs out in front of you and stretch out your feet while leaning back hard into the rock mass. There was a foot hold for you right heel, which, if you were 6 foot tall or more, you could reach, but if you were less than 6 foot you had to let go and slide/tumble and believe that it was there to catch you. Joe and I easily reached the foothold and Marian slid and caught it well, but Deborah had to slide so much further (and thus faster) than any of us. She missed the foothold and fell hard onto the rocky floor (no bruises, thank goodness).
After the cave hike. Photo by person in parking lot.
The beach: down a long tunnel near the bottom of the cave was an open room with a slanting floor. The floor was piled deeply with accumulated sand. We used the “beach” as a rest stop before we did the last big push down to the cave bottom. We sat there, drinking water, resting (steaming, too, in the cool air of the cave!) for about 10 or 15 minutes in total darkness. We spoke very little and just relaxed, soaking in the “caveness” of the place.
References:
Barnes, J. H. and W. D. Sevon. 2002. The geological story of Pennsylvania. Commonwealth of Pennsylvania. Department of Conservation and Natural Resources. Bureau of Topographic and geologic Survey. Educational series 4. Harrisburg, PA.
Cale, D. 1983. From ocean floor to mountain top: the geological story of Laurel Caverns. Foothills Litho Co.. Latrobe, PA.
Van Driver, B. B. 1990. Roadside Geology of Pennsylvania. Mountain Press. Missoula, Mountana.