The Science of Sinkholes: How to Survive
Has anyone noticed that sinkholes have been in the news a lot lately? Here, I’ll refresh your memory. On March 5, 2013, a Florida man lay peacefully in his bed when, all of a sudden, CRASH! He found himself being swallowed by the bedroom floor! No, wait – the floor was being swallowed too!
I’m struck by the horror story here – CNN reports that the man’s brother frantically tried to rescue him, swearing that he could hear his brother calling for help underneath the house.
“’I couldn't get him out. I tried so hard. I tried everything I could,’ he said through tears. ‘I could swear I heard him calling out.’"
Luckily, the brother and four other people escaped from the house. However, rescuers were unable to get close enough to the hole to recover the man’s body, since the ground was still unstable.
That was in Florida; a few days later, a 43-year-old golfer in Illinois saw a divot in the ground, near the 14th hole, and went to check it out. All of a sudden, he disappeared.
An 18-foot fall left him with a dislocated shoulder, and quite panicky. Nevertheless, he hit bottom, and was pulled up by a rope. Somewhat less of a horror story than the Florida incident, but disturbing, nonetheless.
Sinkholes? Seriously? Another thing we have to worry about?!
What ARE sinkholes?
Sinkholes are…well, holes, that form over time due to erosion, and gravity. Often, they reveal themselves gradually, but it is the sudden collapse into a sinkhole that grabs the media’s attention.
And for good reason!
They are usually caused by water that flows below that topsoil; the water turns acidic due to the absorption of carbon dioxide and byproducts of plant metabolism. The acidic water can dissolve limestone or bedrock, and can create underground channels through which more water will eventually flow. This is the process by which underground basins occur.
The constant flow of acidic water continues to erode the bedrock; meanwhile, the top layer of Earth usually stays in tact. However, as the area under the surface dissolves, the lower levels will eventually be unable to support the weight of the topsoil, or the house, or the golf course above it. When this happens, the ground caves in, creating the sinkhole.
There are two types of natural sinkholes that make the news:
- Cover-collapse: This type of sinkhole forms where the topsoil is composed of clay, or other soft material. As the bedrock is eroded, pieces of the topsoil fall into space, causing the top level to become weaker and weaker, until it eventually collapses.
- Cover-subsidence: This type of sinkhole is characterized by small dimensions, the presence of water, and a gradual collapse.
It’s more common than you might think.
Watch out Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, Pennsylvania, and apparently Illinois. According to the U.S. Geological Survey, these are the states most affected by sinkholes.
Though sinkholes aren’t usually deadly, injuries aren’t unheard of. Apparently, “watch out for sinkholes” needs to be put on the list, right up there next to “look both ways before you cross the street”!
Don’t get carried away, though, like Aunt Josephine in Lemony Snicket’s Series of Unfortunate Events. The woman won't touch the phone, the radiator, the refrigerator, the oven, or even the doorknobs, for fear of being injured!
Sinkholes are disturbing because they’re unpredictable – there’s not a lot you can do to prepare for the moment you might find yourself, or your house, or your golf partner plummeting to the center of the earth.
Is there a sinkhole under your house? That’s a difficult question, because there isn’t an efficient way to determine this.
The USGS recommends that people constantly observe their property, watching for cracks in the foundation, or small depressions in the ground surrounding the house.
You can also check with your county office, local or state geological surveys, and the USGS to see if you live in areas underlain by soluble rock.