March 11, 2013
Understanding Sinkholes And Why They Are Dangerous
redOrbit Staff & Wire Reports - Your Universe Online
Ever since a 20-foot sinkhole opened up beneath a Florida home on February 28, swallowing up an entire bedroom and resulting in the death of one of the residents, these natural phenomena have become fixtures in both newspaper headlines and the public consciousness. But what exactly are sinkholes?
“Geologically, a sinkhole is a depression in the ground that has no natural external surface drainage. Basically this means that when it rains, all of the water stays inside the sinkhole and typically drains into the subsurface,” explained Jessica Robertson and Randall Orndorff of the US Geological Survey (USGS).
These depressions are most common in what geologists have dubbed “karst terrain” — regions where acidic groundwater circulates through the type of rock located beneath the land´s surface, causing them to dissolve. Some examples of soluble rocks are salt beds, gypsum and carbonate rock (including limestone). It is that carbonate rock that makes much of Florida highly susceptible to sinkholes.
That apparently includes the town of Seffner, where 37-year-old Jeff Bush was sleeping in his home when a 20-foot wide sinkhole opened up beneath the house and swallowed the man and all of his bedroom furniture sometime around 11 p.m. Eastern, according to USA Today. After the incident, rescue workers spent two days trying to find Bush but were forced to call off the search before the area around the depression became too unstable.
So how do these sinkholes form? According to Robertson and Orndorff: “When water from rainfall moves down through the soil, these types of rock begin to dissolve and spaces and caverns develop underground. Sinkholes are dramatic because the land usually stays intact for a period of time until the underground spaces just get too big. If there is not enough support for the land above the spaces, then a sudden collapse of the land surface can occur.”
An estimated one-fifth of the US in underlain by “karst terrain” and thus susceptible to sinkhole events, according to the USGS. In addition to Florida, the other areas most likely to receive damage related to these depressions include Alabama, Kentucky, Missouri, Pennsylvania, Tennessee and Texas.
In fact, a Bethlehem, Pennsylvania family had to be evacuated from their home following the discovery of a sinkhole believed to be at least 25 feet wide and 10 feet deep on their property, the Associated Press (AP) reported on Monday.
One family member reportedly heard a loud bang early Sunday morning and discovered that part of the house had been swallowed. Safety officials have deemed the home uninhabitable and are now inspecting nearby houses to make sure they are not at risk as well, the wire service added.
Robertson and Orndorff state that it is difficult to tell whether or not a person has a sinkhole on his or her property. They note that there is no easy way to make such a determination at this time, and they recommend that people keep a look out for things like small holes in the ground or cracks in the foundations. People can also contact local officials, state geological surveys or the USGS to find out if there is soluble rock beneath their property.
Sometimes, however, even that isn´t enough. After all, five months before Bush´s death, homeowner Buddy Wicker received an offer from an insurance company to sign up for sinkhole coverage, Jervis said. He decided to sign up, which required inspectors to survey the home to make sure it was safe. After inspecting the property, the insurance company declared it risk-free. Less than six months later, a man living at the property died as a result of the massive depression that opened up, and the home itself ultimately had to be demolished.
“The Seffner sinkhole was more than a human tragedy“¦ It was the abrupt vanishing of 40 years worth of family belongings and a place where his five kids, 13 grandkids and 17 grandkids grew up, learned to walk and went to school,” the USA Today reporter wrote. “Items lost in the sinking and demolition of the home included certificates and other mementos from his 20-year career in the Navy, pictures of great grandparents, letters his wife wrote him while he was in the Navy, clips of grandchildren's first hair, clothes and the diary of his wife, now deceased.”