The Role of Spectroscopy in Studying Caves

Recently, I came back from vacation out west, and part of my trip included a stop at Great Basin National Park, which is located in the small town of Baker, Nevada. At Great Basin National Park, I had the opportunity to take part in a tour of the Lehman Caves, which is a cave system located within the boundaries of the national park.

Yours truly standing in front of the Great Basin National Park sign in Baker, Nevada. | Photo Credit: © Will Wetzel

What is Lehman Caves?

Lehman Caves is the largest cave system in the state of Nevada (1). Several animal species reside in the cave, including bacteria, bats, crickets, spiders, and springtails, to name a few (2). Once discovered by humans, it was popularized and turned into a tourist attraction, and this has caused the ecology of the cave to change. For example, humans have introduced more food sources and increased the temperature of the cave through the installation of lighting (2). These new conditions have allowed plant life to grow (algae), which have provided an additional food source for the wildlife in the cave.

Standing in the lake room inside Lehman Caves. | Photo Credit: © Will Wetzel

What special formations exist in Lehman Caves?

Walking through the main rooms of the cave, I got to see how the stalactites and the stalagmites form in the cave, including formations such as cave turnips, cave bacon, and cave shields.

Cave turnips are speleothems that grow from the ceiling (3). Known for their distinctive bulge in the middle, cave turnips form when calcite water flows over the bubble at the tip of the speleothem, which rounds out the shape of the cave turnip (3). Using uranium-thorium dating, speleologists can determine the ages of these cave turnips. In Lehman Caves, they estimated that they ranged from 60,000 to 250,000 years old (3).

Meanwhile, cave bacon is a type of speleothem that resembles a drapery. These form when water drops flow down a sloped ceiling, building up a line of calcite that forms cave bacon (4). Over time, as the formation grows, these lines become more curved, which gives cave bacon its distinct shape (4).

Cave shields are large speleothems that generally form from cracks in the floor, wall, and ceiling (5). Lehman Caves is reported to have around 500 of them, and I saw a few of them on our tour. These formations develop when calcite-rich water moves through the cracks within the bedrock. Once the water exits the crack, it loses carbon dioxide, and the calcite ends up on either side of the crack, which builds plates of calcite over time, forming the “shield” (5).

An image inside Lehman Caves. | Photo Credit: Will Wetzel

What is the role of spectroscopy in studying caves?

The study of caves is growing in popularity. Originally just an offshoot of geology, there is now a term used for specialists who study caves. These specialists are called speleologists, and they study the formation of caves and cave systems, looking into how they have changed over time.

Thanks to the increased scientific interest in caves and the growth of the field of speleology, more research is being conducted in cave systems, and spectroscopy is finding a unique niche in this branch of science.

Spectroscopy is useful in studying caves because it allows scientists to analyze mineral compositions, organic residues, and even hidden artworks without causing damage to fragile cave environments. This was emphasized in my tour: back when Lehman Caves first opened to visitors (before it was owned by the National Park Service), visitors would take home pieces of the caves as souvenirs, which were usually bits of stalactites. Although these souvenirs were small, taking them did extensive damage to the cave’s ecosystem. Our tour guide explained that everything in Lehman Caves (and caves in general) grows very slowly because of the mineral deposits from the water. As a result, when tourists take an inch or two of a stalactite, that might not grow back for a century or more.

Spectroscopy is used to study caves in several ways. Spectroscopic techniques help identify mineral deposits and speleothems, track ancient climate shifts, detect hidden cave art and pigments, uncover microbial activity, and monitor potential pollutants that could upset the fragile cave ecosystem.

Below, I outline the role of spectroscopy in the abovementioned application areas of speleology.

How does spectroscopy identify mineral deposits and speleothems?

Techniques like Raman spectroscopy, infrared (IR) spectroscopy, and X-ray fluorescence (XRF) can identify the mineral composition of stalactites, stalagmites, and flowstones (6). Understanding the mineral composition of these cave features can help scientists discern important information about not only the history of the cave, but also its previous climate conditions because the growth layers in cave deposits trap geochemical signatures linked to rainfall, temperature, and environmental changes.

What spectroscopic techniques can be used to track climate shifts in caves?

By analyzing isotopic ratios with mass spectrometry (MS)–coupled techniques, researchers can track ancient climate shifts recorded in calcium carbonate formations (7). Organic matter trapped in cave sediments can also be studied with spectroscopic methods to reveal past ecosystems.

How are spectroscopic techniques being used to uncover hidden cave art and pigments?

Hyperspectral imaging and Raman spectroscopy allow scientists to detect faint or invisible pigments on cave walls. These techniques, along with magnetic susceptibility and reflectance spectroscopy, can uncover ancient cave paintings that are no longer visible to the naked eye because of fading, mineral deposits, or erosion (8). Importantly, these methods are non-invasive, so the artworks are preserved while still being studied.

What spectroscopic techniques have been used to detect microbial activity?

Caves host unique microbial ecosystems (1). Fluorescence spectroscopy and UV-visible spectroscopy are sometimes used to detect microbial activity, biofilms, and organic residues (9). This is especially important for understanding extremophile life and the possible analogs to extraterrestrial habitats.

How can spectroscopy be used to monitor and detect cave pollutants?

Spectroscopy is applied to monitor cave conditions and detect pollutants or human impact on fragile environments (10). For example, portable spectrometers can track changes in mineral surfaces or the growth of contaminants without requiring sampling.

What can we expect in the future?

The study of caves is growing in popularity, and spectroscopic instrumentation is becoming more versatile and effective. Thanks to the rise of portable instrumentation, speleologists are now able to study different things in caves that were previously unexplored. In particular, measuring stalactites, especially cave turnips, can be difficult because of their size and the small space in the cave. Portable instrumentation makes it easier for experiments and research to be conducted.

Cave systems are some of the most fragile ecosystems on Earth. Therefore, any method that is used has to be nondestructive. Spectroscopy allows researchers to learn more about the chemical and physical history of a cave system without damaging it, which positions these techniques as potential options going forward for researchers conducting work in cave systems.

References

1. National Park Service, Lehman Cave Tours. NPS.gov. Available at: https://www.nps.gov/grba/planyourvisit/lehman-caves-tours.htm (accessed 2025-09-08).
2. National Park Service, Cave Life. NPS.gov. Available at: https://home.nps.gov/grba/learn/nature/cave-life.htm (accessed 2025-09-08).
3. Johnston, R. Uncovering the Mystery of Cave Turnips. NPS.gov. Available at: https://www.nps.gov/articles/000/cave-turnips-2023.htm (accessed 2025-09-08).
4. National Park Service, Speleothems. NPS.gov. Available at: https://www.nps.gov/subjects/caves/speleothems.htm (accessed 2025-09-09).
5. National Park Service, Cave Shields: The Wonder of Lehman Caves. NPS.gov. Available at: https://www.nps.gov/grba/learn/nature/cave-shields.htm (accessed 2025-09-08).
6. Clark, R.; Boardman, J.; Mustard, J.; et al. Mineral Mapping and Applications of Imaging Spectroscopy. Presented at the 2006 IEEE International Symposium on Geoscience and Remote Sensing, Denver, CO, USA, 2006, pp. 1986–1989. DOI: 10.1109/IGARSS.2006.514
7. Patrick, E. L.; Mandt, K. E.; Mitchell, E. J.; et al. A Prototype Mass Spectrometer for In Situ Analysis of Cave Atmospheres. Rev. Sci. Instrum. 2012, 83, 105116, DOI: 10.10163/1.4761927
8. Wetzel, W. Magnetic Susceptibility and Reflectance Spectroscopy for Non-Invasive Detection of Cave Art Beneath Calcite. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/magnetic-susceptibility-and-reflectance-spectroscopy-for-non-invasive-detection-of-cave-art-beneath-calcite (accessed 2025-09-09).
9. Balestra, V.; Bellopede, R. Microplastic Pollution in Show Cave Sediments: First Evidence and Detection Technique. Environ. Pollut. 2022, 292 Part A, 118261. DOI: 10.1016/j.envpol.2021.118261
10. Zhang, R.; Liu, Z.; Xiong, K.; et al. Analysis of the Three-Dimensional Fluorescence Spectroscopy Characteristics of Dissolved Organic Matter in Groundwater from a Subtropical Cave in Dry Season—Daxiao Cave in South China Karst. Water 2021, 13 (24), 3574. DOI: 10.3390/w13243574