Cucumber Falls illustrations lesson in erosion
Fall, cooler days and less sun doesn't necessarily mean that walks in the outdoors are over for the year.
The days still have some warmth, insects have gone into hiding, and with the leaves off the trees, the views are expansive. With that in mind, may I suggest a wonderful short walk for a late fall day -- a trip to Cucumber Falls in Ohiopyle State Park, Fayette County. Once you get to the falls, it's a great place to enjoy the rugged scenery, and the area is a perfect demonstration of how waterfalls are formed.
Once in Ohiopyle, stop at Ohiopyle Falls, where the Youghiogheny River plunges over a ledge -- forming the largest waterfall in Western Pennsylvania. Make a mental note of the falls and their location. You will need to think about that when you are at Cucumber Falls.
After driving to the Cucumber Falls parking area, the walk on the trail is very short and, almost immediately, you are looking down into a deep valley. To the left, a stream falls over the lip of the flat rock ledge. This is Cucumber Falls.
Park brochures describe Cucumber as a "bridal veil" waterfall. At this time of the year, with the stream at a low flow, you get a sense of the wispy nature of the cascade and, thus, the description. The total drop is about 30 feet, 10 feet more than Ohiopyle Falls.
The trail switches back on a set of wooden steps and descends into the valley. At several places, there are views of the falls and the rock-clogged stream flowing to the Youghiogheny River. When the trail gets to the level of Cucumber Run, it continues for a short distance to the Youghiogheny River.
At the confluence, you have a expansive view. The rapids in front of you are Cucumber Rapids, named after the stream, of course.
The name of the stream, Cucumber Run, by the way, isn't because it is shaped like a cucumber, is the color of a cucumber, or has the smell of a cucumber. Actually the name has nothing to do with cucumbers at all. Cucumber Run is named for the abundance of one species of magnolia tree, the cucumber magnolia ( Magnolia acuminate ), that still is found in the watershed.
Let's step back for a moment and look at the region.
The Laurel Highlands have a lot of waterfalls, from knee-high to 30-foot precipitous drops like Cucumber Falls'. The reason for all the falls and cascades is the geology.
The Laurel Highlands, officially the Allegheny Mountains, were formed when a cake-layer-like foundation of sedimentary rocks were folded into wave-like undulations. The process took a very long time and was complex, with several cycles of erosion and uplift.
The primary reason for the abundance of waterfalls in the Laurel Highlands is that the layers of rock are of varying hardness. Shale, slate, coal and limestone are softer rock layers and are easily eroded by water and ice. On the other hand, sandstone, particularly the Pottsville Sandstone that is found throughout the region, is a hard, dense rock that resists the power of water and ice and erodes slowly.
When a stream flows from the uplands, it cuts into the rock layers. It erodes through softer rock layers easily. However, when the stream hits the dense Pottsville Sandstone, erosion slows, and the stream often flows on top of the Pottsville Sandstone for a long stretch.
Each waterway has different volumes of water and thus erodes the rock at the bottom on the stream at different rates. Small streams cut through rock more slowly than large rivers. Also, each of the small streams ultimately meets larger streams and, finally, a river. In the Laurel Highlands of Somerset and Fayette counties, the river is the Youghiogheny, or the Yough to those of us living here.
Now, while you are standing at the confluence of Cucumber Run and the Yough, think about where you were moments before, at Ohiopyle Falls. Looking upstream from the mouth of Cucumber Run, you can't see those falls. They are well out of sight around the bend.
Waterfalls are temporary features on a landscape. They are always moving upstream as they cut into the foundation rocks of a region. However, measured in human time, the movement is very slow, mostly imperceptible. Also, different volumes of water cut rock faster or slower, and thus move at different speeds.
Now, turn around, and look upstream on Cucumber Run. The falls are not very far away at all, especially compared to where the falls on the Yough are now. Both waterfalls, on the Yough and on Cucumber Run, are falling over the same ledge of sandstone. At one time, both the falls of the Yough and of Cucumber Run were in pretty much the same place. Since then, they have moved at different speeds and now are different distances from the original spot, even though they are falling over the same layer of sandstone. Because of the ubiquitousness of the Pottsville Sandstone in the Laurel Highlands, nearly every waterfall found there is flowing over that same layer.
Now, walk back up to Cucumber Falls to look at how waterfalls are formed.
Cucumber Run falls off a layer of Pottsville Sandstone. All the softer layers above the Pottsville have been eroded away.
Below the sandstone are other layers of rock, and at this location, the layers below are softer. They are not eroded so much by moving water but by freezing water during the winter. Moisture penetrates small crevices, freezes and expands. Just as easily as the freeze-thaw cycle creates potholes, it breaks the softer layers below the sandstone into small pieces that fall away from the face of the ledge.
The soft rocks fall away, leaving the Pottsville Sandstone cantilevered above the valley. Finally, the ledge becomes too heavy to support itself and large chunks fall into the valley below. Look around below the falls and you will find these large chunks of sandstone that once were part of the protruding ledge.
At Ohiopyle Falls, the softer ledge below the falls is hidden by the river, but the same thing is happening there as at Cucumber Falls. Little by little, the underpinnings erode, the ledge becomes too heavy, and chunks break off and fall. Chunk by chunk, the falls retreat upstream at a pace related to the amount of water in the stream or river.
What happens to all those chunks?
They are now subject to the direct pounding of water and the silt, sand, gravel and small rocks carried by the streams. Piece by piece, grain by grain, big chunks are ground into small rocks and finally sand, and carried away by the stream and then the river.
All this takes a lot of time, and even if you stop back next year, 10 years, 50 years or 100 years from now, you'll see very little difference. Erosion is a process that happens on geologic time, not human time.
Additional Information:
If you go
To get to Cucumber Falls:
From the Pennsylvania Turnpike , use Exit 91, Donegal, then follow Route 31 east to Route 381 to Ohiopyle State Park.
From the south , U.S. 40 is the best route. Go to Farmington, then take Route 381 north to Ohiopyle.
From central Somerset County , Routes, 30, 31 and 653 go over Laurel Ridge to Route 381.
From southern Somerset County , go through Confluence on Route 281 to Sugarloaf Road, and then over the Laurel Ridge to Ohiopyle.
From the Falls Overlook parking lot in Ohiopyle, turn right onto Route 381 and go south for a short distance and over a bridge. At the south end of the bridge turn right again, up a hill. Just over the first rise and downhill a bit, you will find a parking lot on the right. Park there and head for the trail to Cucumber Falls.
