Lehman Caves' Climate Before, During and After the COVID Closure

First published in The Midden*, Great Basin National Park's newsletter, Vol. 21, No. 2, Winter 2021. By Gretchen Baker, ecologist.*

Lehman Caves was closed to the public from March 19, 2020, to May 22, 2021, because of COVID — possibly its longest closure since tours began in 1885. (In 1944, during World War II, it had only 872 visitors all year, so it was probably closed for a few months then.)

The closure was bad for sharing one of the park's great resources, but it allowed something new: with people in the cave nearly every day, year after year, the park had never been able to record its baseline climate.

Figure 1. The relay panel in the Doghouse, Lehman Caves, where the readings on this page were logged. NPS photo by Gretchen Baker.

Temperature and humidity dataloggers were installed at several places in the summer of 2019, as part of the cave lighting project, recording every hour.

Normal operations

Before the closure, the readings swung every day. Beside the Doghouse relay station, temperature rose from about 52 °F to 60 °F, and relative humidity fell from near 100% to below 80% — sometimes below 70%.

Why? When the cave's power comes on, it runs to a main transformer at the Giant's Ear and on to four relay panels, each with a small heater to keep its electronics dry. So heat comes not only from light bulbs and human bodies, but from those heaters too.

Figure 2. Temperature and humidity at the Doghouse under "normal" conditions, September–December 2019.

• Smaller swings after November 1, when tours drop from four a day to one and the lights are on for less time.
• A red arrow marks a stretch when temperature stayed high and humidity low — the lights had been left on overnight, with a big effect on the cave.
• A purple arrow marks the opposite — low temperature, high humidity: Thanksgiving, one of the three days a year the cave normally closes.

Closed: 2020

From March to December 2020, temperature stayed flat for most of the period, and humidity sat at 100% for months. The small blips are when lights went on for cultural resource surveys and quarterly biological monitoring. From March to October, with the lights out, the cave settled into what might be called its baseline, free of tours and infrastructure.

Figure 3. Temperature and humidity at the Doghouse relay panel during the closure, March–December 2020.

Reopening: 2021

In January and February 2021, temperature held steady at about 52 °F. It fluctuated more in March, when lights were on for a few days of cultural resource work, then settled until training in May. Once regular tours resumed at the end of May, the big daily swings returned.

Figure 4. Temperature and humidity at the Doghouse, January–July 2021; the return of regular tours at the end of May is easy to spot.

Look at the minimum temperature once the lights come on daily: it creeps up a little each day, and so does the maximum. The cave never fully recovers — it just keeps getting warmer.

What happens next

Reducing these swings is one goal of the new cave lighting system: turning lights on only when needed, and using newer technology that does away with the extra heaters, should help restore a more natural cave climate.

Sources

• National Park Service, Great Basin National Park, "Lehman Caves Temp and Humidity before, during, and after Closure," The Midden, Vol. 21, No. 2, Winter 2021. https://www.nps.gov/articles/000/lehman-caves-temp-and-humidity-before-during-and-after-closure.htm
• The article puts the closure at 427 days, which does not match its dates; only the dates are given here.
• Rewritten in hubnx's own words.