Geological landform evolution - Earth Science Lesson
Is this Alabama’s best kept secret? Quite possibly.
Maybe it’s the lack of signage, directions or simply not being mentioned in publications. It's time to share the secret
Pisgah Gorge is located in Jackson County, northeast corner of Alabama. The region is known as Sand Mountain, a plateau sixty miles wide and about twenty miles long. There are three creeks forming a canyon that runs for almost two miles and drops more than a thousand feet to the Tennessee River
Documentation on the area is sparse. The Friends of the Gorge had some interesting information on their site http://friendsofpisgahgorge.org
Pisgah is Hebrew for mountain top. During the Trail of Tears forced removal, several Cherokee escaped and hid out in Pisgah Gorge. Those that were recaptured were held in a unique karst topology geographic feature now known as the Indian Penitentiary, because there was only one opening that needed to be guarded. At least one Cherokee was never captured and has been reported to still be seen in The Gorge
When the water level is right, practically a flood, Pisgah Gorge is a world class whitewater kayaking destination where the river drops almost 700 feet over about 6 miles not counting a couple miles of flat water across Jones Cove, although 500 feet of the total drop occurs along a 2 mile section in the middle of the run that begins with a 20 to 30 feet waterfall.
Modern GPS maps still contain an error that leads to bridge cross the Gorge than no longer exist. A hiking group once got lost on an exploratory hike while using a map 50 years out of date and expecting to find and use this bridge as an alternate end point for their hike.
Background information on terminology and formation
This is a unique geologic area. Pisgah Gorge is almost hidden, and as you walk the path, you begin to hear the water. It's a faint sound at first, then getting louder as you walk closer to the edge. Your eyes are finally rewarded with the beautiful waterfall. It's remarkable and the opening/drop is huge. How did that happen?
So what is a gorge? According to National Geographic https://www.nationalgeographic.org/encyclopedia/gorge/ a gorge is a narrow valley with steep rocky walls located between hills or mountains. The term is French, the word gorge means throat or neck.
A gorge is an erosional valley carved by the action of a river. ... Many gorges and canyons are connected to limestone and karstification. Often the process of cave development and collapse produces gorges. But the biggest canyons are formed simply by a combination of uplift and erosion or in connection with glaciation.
A number of natural forces form gorges. The most common is erosion due to streams or rivers. Streams carve through hard layers of rock, breaking down or eroding it. Sediment from the worn-away rock is then carried downstream. Over time, this erosion will form the steep walls of a gorge. The flooding of streams or rivers increases the speed and intensity of this erosion, creating deeper and wider gorges.
Geologic uplift also forms gorges. Geologic uplift is the upward movement of the Earth’s surface. Geologic uplift is often associated with earthquakes and orogeny, the process of creating mountains. During geologic uplift, rock layers beneath the Earth’s surface bump against the surface layers. Softer layers of surface rock erode. Many geological discoveries have been made at gorges because gorges often expose layers of rock that go back thousands of years.
Erosion and geologic uplift often work together to create gorges. Parts of streams or rivers can be elevated, along with land, during the process of geologic uplift. As rivers or streams flow across this uplifted surface, waterfalls form. Over time, the power of the waterfall erodes the softer rock layers underneath, causing the original river bed to collapse and create a gorge.
Pisgah Gorge was formed as a result of a change in rock type at a waterfall. At the base the pressure and hydraulic action of the falling water causes the softer rock which is underneath to erode forming a plunge pool.
Jackson County is in the Cumberland Plateau, one of five physiographic areas of Alabama. The topography is karst, composed of Paleozoic sandstone, shale and limestone.
Over time, the beautiful waterfall at Pisgah Gorge was so powerful, eroding rock layers, and it caused the original river bed to collapse and thus created the gorge.
Pisgah Gorge is also included in Waterfalls of Alabama, listing the fourteen top waterfalls in the state. Two of the waterfalls here are over 100 feet.
Logging Requirements –
Please post a picture with the waterfall as background, including you or your group if possible.
- In observing this amazing area, how do you think it formed? There’s some background information to read in the text, but share your thoughts.
- Have you ever visited another gorge? Where? How does the formation compare to this area?
- Observe the waterfall. Would you think your visit today is about the average flow or is precipitation above normal? Is there a drought that could impact the amount of water? What influenced your conclusion?
Optional (include in your log or share with your group)
At the overlook there is a seating area that was built for the Middle School students. You may have noticed the many electric plugs for tools to help them with their scientific research. It was built with grant money-quite an accomplishment for such a small town.
- Sit quietly and listen to the sounds. We get so busy, places like this let us recharge. Were any sounds unexpected? This area is just above the old stockade, used during the Trail of Tears. Do you think the people waiting there heard the same type of sounds that you did? Did you notice any echo, given the size of this space-do you think it would be possible? Explain your ideas.
- We live about ten minutes away from here. Do you think the water here could have come from our pond recently? Do you agree or disagree? Explain.
I listed some additional waypoints for exploring. Did you visit the mill dam remains? Find an old home place? See something interesting in nature’s beauty? Did you walk down to the natural bridge?
- Tell me you favorite thing about your trip today
- Would you plan to return in the future?