Downloading data loggers in Lehman Caves. Image from the National Park Service's page
Do tourists change the climate inside a cave? In 1969, a study by Stark looked at how tourism affected the air in Lehman Caves, in Great Basin National Park. Nearly 50 years later, researchers from Slovenia's Karst Research Institute, the park and the University of Nevada, Las Vegas took a fresh look, logging air temperature year-round.
Six stations
On August 6, 2015, the team placed two Van Essen data loggers, accurate to ±0.01 °C, in the cave (stations GBNP 1 and GBNP 2). Four stations already existed: Entrance Room, Queen's Bathtub, Cypress Swamp and Talus Room. They sat at different distances from the entrance, and two were off the tour route. Hourly readings were compared with monthly mean outside temperatures.
The monitoring stations; GBNP 1 and GBNP 2 were added for this study. North is at the top. Image from the National Park Service's page
What the stations showed
| Station | Where | Temperature |
|---|---|---|
| Entrance Room | nearest the natural entrance | swings widely, over about 4 °C |
| GBNP 1 and Queen's Bathtub | close together, about midway along the tour | range over about 1 °C |
| Cypress Swamp | farther in, on the tour route | a weak seasonal signal |
| Talus Room and GBNP 2 (West Room) | off the tour route, away from the entrance | nearly constant all year |
In winter, when the outside air is colder than the cave, cold air flows in through the natural entrance — the "chimney effect" — and stations near the entrance cool. In summer, the cave warms from warmer outside air and from more visitors, with their bodies and lighting.
So the tour route behaves like a thermal cave, with air flow clearly different in summer and winter, while the remote Talus and West Rooms behave like a barometric cave, barely changing between seasons.
Hourly air temperatures at six stations and the monthly outside mean, July 2015 – August 2016. Image from the National Park Service's page
Signs of a human footprint
- The four tour-route stations showed bigger daily swings and higher summer temperatures — possibly visitors' effect on top of the chimney effect.
- At Queen's Bathtub and GBNP 1, the air stayed warm until October 2015 — two months after visitor numbers fell, and one to two months after the outside air cooled.
Hourly air temperatures at five stations beside monthly visitor numbers, July 2015 – August 2016. Image from the National Park Service's page
Warmer than it should be?
| Comparison | Temperature |
|---|---|
| Outside air, July 2015 – July 2016 | 9.2 °C |
| Lehman Caves at GBNP 1, a year from August 2015 | 1.9 °C warmer than outside |
| Little Muddy Cave — not a show cave, 0.5 km away and about 100 m lower — November 2005 to November 2006 | 9.7 °C, 1.5 °C cooler than Lehman Caves (GBNP 1 and Talus Room), and closer to the outside air |
| Stark's readings, November 1968, over 8 hours with the lights off | 10.1–11.4 °C, mean 10.8 °C |
| GBNP 1, November 2015 | about 0.6 °C higher than in 1968 |
Two things could keep a cave warmer than the air outside: heat from the Earth's interior, or heat from visitors and lights. The first seems unlikely here — there are no known hot springs or signs of active volcanism within 20 km — though it deserves more study.
The findings support the idea that human activity is warming Lehman Caves above natural levels, but the authors say more research is needed to confirm it.
Sources
Based on Stanka Šebela (Karst Research Institute, ZRC SAZU, Slovenia), Gretchen Baker (Great Basin National Park) and Barbara Luke (University of Nevada, Las Vegas), "Air Temperatures in Lehman Caves," The Midden, Winter 2018, National Park Service; a work of the United States government in the public domain; rewritten in hubnx's own words.
이 페이지가 속한 매거진Great Basin National ParkThe Midden - Great Basin National Park: Vol. 18, No. 2, Winter 2018
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