Pellissippi State student Jared Dockery didn’t have to take a “Journey to the Center of the Earth” to understand what’s happening far beneath the surface.
Months before he and Professor Kathleen Affholter viewed the 2008 film inside Cherokee Caverns, Dockery and Affholter were visiting the cave on Oak Ridge Highway weekly to conduct experiments.
Dockery, a 33-year-old veteran of the U.S. Air Force, launched the independent study with Affholter in spring 2019, to fulfill his Environmental Science requirement.
“I was always interested in geosciences, but specifically in geology the last year or two,” said Dockery, who graduated from Pellissippi State in May 2019 with an Associate of Science in Geosciences and transferred to the University of Tennessee, where he is majoring in Environmental Science. “I just find caves fascinating – that these structures have taken thousands, some even millions, of years to form. And I find that amazing because our lifespan is so insignificant compared to that.”
Affholter, who previously had Dockery in her Physical Geology class, helped him design an experiment using Pellissippi State’s new portable Vernier CO² gas sensors.
The experiments were twofold: (1) to determine how the pH – the acidity or alkalinity – of rainwater changed after it seeped through layers of dolomite into the cave and (2) to compare the amounts of carbon dioxide – CO² – present in various parts of Cherokee Caverns.
“Scientists worldwide study caves and ‘show caves,’ those that are open to visitors,” Affholter explained. “Understanding CO² concentrations in caves is not only important for cave conservation, but also for visitor health. The amount of CO² in a cave affects how the rock will dissolve and how the speleothems will form. In addition, elevated CO² in caves can be noxious to human health.
“Understanding how our cave works contributes to the understanding of caves worldwide,” she added. “Cherokee Caverns is open certain times of the year for movies and holiday events, so it is at least part time a ‘show cave.’”
At the beginning of the spring 2019 semester, Affholter and Dockery hiked a short distance above the cave, where they took three clean gallon jugs and staked them to the ground to collect rainwater. Once it rained, they tested the water and found that its pH was 6, which is slightly acidic.
They also measured the CO² level outside the cave, which was 410 parts per million at the time.
Then it was time to move the experiments inside Cherokee Caverns, which have been used as a tourist attraction off and on since 1929. Although the cave is only open for special events, caretakers Jim and Mike Whidby graciously allowed Affholter and Dockery access to conduct their research.
“We wanted to see what happens to water when it goes into the cave,” explained Affholter, who has taught at Pellissippi State for 13 years. “As rainwater infiltrates through the rock, chemical reactions occur that create CO² gas that comes out the soda straws (the earliest growth of stalactites) when they drip water. That’s why CO² gas is measured in higher concentrations in caves than in the outdoor air — because it degasses from soda straws in the cave.”
The easiest – but most tedious – part of the Cherokee Caverns experiment was collecting enough drips from the soda straws to test the water’s pH levels. Affholter and Dockery selected a section of the cave where they could reach the soda straws without a ladder and hovered underneath the shining wet formations, moving a small glass jar from straw to straw, catching each drip as it fell.
“What we learned is that the water from the drips got much more basic – moving from a pH of 6 to a pH of 8.3,” Affholter explained. “That is something you would learn in chemistry, but it’s nice to see it happen in real life.”
The experiments to measure the amount of CO² the drips were releasing into the air were a little trickier. Affholter and Dockery couldn’t be too close to the soda straws or their breath would affect the readings on the CO² monitors – and they also couldn’t lie in wait for the drips to fall on their own.
“That’s kind of the fun part of an experiment: problem-solving,” Affholter said.
“You use what you have,” he noted. “We would literally dig in our trunks. One day we thought we were going to have to use my fishing pole (to reach the drips from a distance), but we went with my extendable ice scraper because it was more sturdy.”
The two ended up taping a CO² monitor and a cell phone with the monitor’s app to a Swiffer mop Affholter had in her car. They stood back, held their breath and gently knocked down the drips with Dockery’s ice scraper and a long stick from outside without damaging the soda straws.
Affholter and Dockery confirmed that the drips were releasing CO² into the air of the cave: the carbon dioxide level in Cherokee Caverns was 530 parts per million, compared to 380 parts per million outside at the time.
“CO² is an important gas for caves as it is involved in the chemical reactions that govern carbonate rock dissolution (how limestone and dolostone dissolve) and speleothem formation,” Affholter explained. “Tennessee has the most caves in the United States because we have abundant limestone and dolostone, which can, over geologic time, dissolve due to acid rain and form caves with speleothems (soda straws). It is important to understand how to preserve them.”
The independent study gave Dockery the opportunity to write his first scientific abstract.
“This experiment shows a need for a general understanding of the burdens that our soils and underlying bedrock are experiencing,” Dockery said. “As rainwater reacts with carbon dioxide from the soil and atmosphere, it becomes carbonic acid and dissolves the calcitic/dolomitic rock underneath. This does produce the spectacular cave systems that people often visit, but it also creates weak points in the terrain and possibly drainage issues, eventually collapsing into sinkholes.
“Homeowners especially could benefit from understanding what they are building their new home on and if engineering precautions need to be taken,” he added.
Although Dockery graduated in May, he and Affholter visited Cherokee Caverns again in July to test their theory that special events inside the cave would raise CO² levels because we breathe in oxygen and breathe out carbon dioxide.
“We went to the cave and watched the movie ‘Journey to the Center of the Earth,’ and we took the CO² monitors and tested the amount of CO² in the area where people were watching the movie,” Affholter explained, noting the readings were as high as 5,000 parts per million. “Of course, it was elevated as people were breathing out CO² as normal. I went back a few days later and, to my surprise, the CO² was still elevated.
“I’m not totally surprised now, when thinking about it in hindsight,” she added. “There isn’t a lot of air circulation in the cave so it would take a while for the CO² to dissipate. I don’t know how many days it takes for it to come down to the level it was at when we first visited the cave.”
Dockery said he’d like to go into water conservation after he finishes UT or perhaps hydrogeology, which would combine the study of water and rocks.
“I’m all for offering classes like this,” he said of his independent study with Affholter in Cherokee Caverns. “People should be more educated about the physical structures of our earth instead of just going out and destroying them without knowing what kind of harm they’re doing.”