In Florida, where I live, there is the occasional bizarre headline, and always with a terrifying picture, about the latest thing or things the ground has decided to swallow up whole. Usually something heavy and substantial, too, like a car, or a house. These horrifying spectacles (or maybe we should call them events) are known as sinkholes. The phenomenon didn’t make any sense to me until I took the time to look into the science. Then I was simply surprised (and grateful) that these gaping holes occur as seldom as they do.
(Note: I suppose the term “seldom” is relative, since a map of Florida designed to show where sinkholes exist looks remarkably similar to Swiss cheese, or a moonscape that’s full up and simply unable to accommodate even one more crater. Although sinkholes are nothing new, the idea of new ones forming as a result of human activity certainly is…read on).
One word—limestone (that’s actually two words pushed together, isn’t it?) Florida has bedrock made up, in large part, of this stuff, as well as dolomite, gypsum, and some other minor actors to round out the mix. Naturally acidic rain falling on the earth percolates into this limestone, physically (chemically) altering the rock, slowly eating away at the delicate substance each time there is precipitation. After long periods of this persistent eroding action, the landscape may ultimately find itself too weak to offer support. The result is a cave-in, sometimes to the extent that stuff like homes and neighborhoods get gobbled up (there must be a recipe for a bad sci-fi movie in there somewhere).
From a geologist’s viewpoint, sinkholes are simply the natural result of erosive processes occurring throughout the world. In fact, all across the planet there are numerous tourist attractions centered around one or more sinkholes. Many are truly spectacular to behold! You can discover these beauties for yourself simply by typing “sinkholes” in your favorite search engine, then enjoying the colorful images as your visual reward (be sure to check out Devil’s Sinkhole in Texas, or Sarisarinama Sinkholes in Venezuela).
Many of Florida’s lakes are the result of sinkholes. One indicator that a lake may have been formed that way is its characteristic round shape. For example, Kingsley Lake in north central Florida, when viewed from the air, is so perfectly round that pilots have dubbed it the Silver Dollar Lake.
There are times when, instead of the roof caving in, it stays intact, resulting in breath-taking limestone caverns one can step into and explore (sort of…you might be told not to touch anything, and don’t go blazing any new paths in the darkness). Florida Caverns State Park is one such example, and the guided tour through the tunnels is well worth the trip (but again, don’t touch—you will be reprimanded (snicker)).
This article isn’t about just touting the visual splendor –like lakes and caves and such—that can result from sinkholes or other geological activity. In fact, it originated as a result of my discovery that many cities around the world are slowly sinking into the ground as a result of a phenomenon known as subsidence—the scientific name for what I’ve been discussing—the ground giving way, slowly or abruptly, compromising the structural integrity of anything that might be resting on top. The most startling information to convey here is that, in a growing number of instances, subsidence is occurring (or is at least being accelerated) as a result of human activity.
Urban development, including housing and businesses, roads and parking lots, retention ponds, well digging, aquifer access, fracking…all can contribute to shaking up the stability literally under our feet, causing undesirable consequences like…well, like sinking cities.
On this website, which revolves mainly around “all things water,” I include in these discussions all the ways in which humanity is increasingly influencing the course of future civilizations with the actions we take today. Sinking cities is just one of the hundreds of topics we talk about, including how such situations are caused, as well as the many ways in which science attempts to mitigate the damage when we humans find ourselves slipping in the mud, trying not to be eaten whole by a bus-crushing sinkhole.
Check out these related articles on my website. Enjoy and sincere thanks for stopping by!