Today in Holes and Pits: A favorite Texas Local Hole with–bonus–weird military history. Devil’s Sinkhole in Edwards County, Texas, is a 40 x 60 ft funnel-shaped sinkhole that drops down 350 ft. The sinkhole opens into a cavern that is 1,081 ft across at its widest point and is a virtual Mexican free-tailed bat hotel (occupancy: 3 million bats, or about 200 bats per square foot of cave).
In the 1940s, the U.S. government performed research in this and many other bat-friendly caves across the American southwest. Their goal was to develop a prototype “bat bomb,” a bizarre military widget that corralled thousands of bats (each outfitted with a tiny incendiary device) into a bomb shaped metal casing. Theoretically, these “bat bombs” would be dropped via aircraft into enemy Japanese territory, where the liberated bats would seek out the roofs and eaves of buildings (and then covertly explode their little bat selves). Somewhat predictably, the bat bomb project was canceled in 1944.
Outside of its elite military function, the Devil’s Sinkhole is a showpiece for Texas geology. The sinkhole is a portal into the vast karst landscape of the Edwards plateau. Karst features are formed by the dissolution of soluble rocks (in this case, limestone). The breakdown of these rocks creates voids, which in turn fill up with rainwater, becoming aquifers. 25% of the world’s population obtains its drinking water from karst aquifers; in the us, over 40% of the groundwater that becomes potable water comes from karst features.
This leads one to contemplate the amount of bat poop entering the Edwards Aquifer through openings such as the Devil’s Sinkhole. It also makes the bats the keepers of the entrance to the caverns of our water, some of the first affected parties in an ecosystem damaged by toxic waste. Healthy cave landscapes are a piece of safe drinking water. Canary in the coal mine, Bat in the Karst Feature.
To learn more:
- Texas Speleological Survey, Devil’s Cave: https://www.texasspeleologicalsurvey.org/wildcaves/tssdevilsinkhole.php
- Bat Bomb: World War II’s Other Secret Weapon: https://utpress.utexas.edu/books/coubat
- Karst is a Landscape: https://www.uky.edu/KGS/water/general/karst/karst_landscape.htm
- Karst Topography: https://geomaps.wr.usgs.gov/parks/cave/karst.html