Here’s a news teaser that will keep you watching: ”Is your house about to be swallowed whole by the earth? Find out tonight after the game!” As crazy as that might sound, real stories about the ground literally falling out from under people in Florida are making big news right now. Whole buildings are disappearing into sinkholes, seemingly without warning, and it’s a trend that’s increasing.
What are sinkholes? Why do they happen and what can we do about them? Some sinkholes are part of a natural process that goes back as far as we can see into geological time. Others are triggered by human activity.
Sinkholes? Why Florida? Why Now?
Sinkholes are actually common all over the country, including parts of Alabama, Kentucky, Missouri, Tennessee and Texas. The reason Florida is in the news right now is because population growth and land development has sped up the process in a region where geological conditions for sinkholes were already ideal.
The geology of Florida is a major factor. It turns out that even though it may appear quite solid and stable to us, the ground that’s holding up our homes, streets and landscapes is constantly moving and changing beneath our feet. The surface we live on is actually a thin layer that’s unevenly distributed over different kinds of subsurface rock. In Florida, that’s mostly carbonate material like limestone which is very easily eroded by fast moving groundwater that’s constantly rising and falling.
Sinkholes – Why Florida Is Especially Vulnerable
Around 20,000 years ago, geologists estimate that the sea level around Florida was anywhere from 200 to 300 feet lower than it is today, exposing vast expanses of relatively soft carbonate rock to random sculpting by rain and other natural forces. Rising seas gradually deposited other materials that filled in the unevenly weathered surface, each reacting differently as subterranean aquifers built up around them.
Over millennia, some of this material either dissolved or was carried away by rapid and powerful underground streams, leaving voids as small as your fist up to massive subterranean caverns. The most dangerous kinds of sinkholes, like the recent big one in Florida, are called ”cover-collapse.” Geological forces gradually weaken the harder surface material (called the “overburden” by geologists) until it collapses into the cavity below. Unfortunately, anything sitting on that patch of ground falls with it.
The science behind all this gets pretty fascinating. For the huge chunks of time and physical space we’re talking about, the natural balance of the system is surprisingly delicate. There’s the relationship between rainfall and aquifer levels, subtle chemical reactions between the rock and the water and even cases where processes reverse themselves more than once. Groundwater flows can switch direction under extreme conditions and you’ll find precipitated rock formations like stalactites that strangely dissolve and reform over time, depending on the mineral content of the surrounding water.
Why Sinkhole Science Is Relevant Today
Sinholes are a completely natural phenomenon that would be happening anyway. The reason they seem to be occurring more often and more severely is that human intervention can accelerate the process. Natural sinkholes tend to happen slowly. The sudden and more catastrophic ones seem to be triggered by activities like construction, paving, farming, irrigation and groundwater pumping which can profoundly alter the state of the aquifer below. Changes in underground water pressure lasting just a few weeks to even a few hours can be enough to trigger one or more cover-collapse events.
Think of it as a gigantic underground plumbing system that stretches for miles in all directions. It all has to do with the movement of groundwater through different kinds of surface and subsurface materials. Every time we build a structure or lay down pavement were changing the way runoff water interacts with a vastly interconnected system – not to mention the surface loads that a particular piece of ground has to bear. When you add rainfall changes or drought, the odds of a sudden collapse go way up.
This point is supported by a strong correlation between waves of sinkhole activity and major development booms in Florida during the 1930s and 1960s, plus data that’s been tracked up to the present day. The spikes virtually always coincide with increased groundwater pumping as land developers kept pushing further inland to meet the growing demand for fresh water.
The more you think about it, the more you realize how interdependent things are. Remember the record cold temperatures in Florida a while back? The farmers pumped warm water out of the aquifer as freeze protection for the crops. Then you have periods of low rainfall and drought. All of this influences groundwater conditions and reduces supporting pressure in areas vulnerable to collapse.
Keeping Your Home Above Ground
What do sinkhole companies like Foundation Technologies recommend if you live in a known sinkhole zone? Between 2006 and 2010 CNN estimated that there were close to 25,000 sinkhole-related insurance claims filed in Florida adding up to a value of nearly $1.4 billion. While there’s no immediate need for panic, there are telltale signs you can watch for that can give you early warning.
- Do you live in an area where fresh water demand is going up?
- Are there cracks, separations, mold or mildew around foundations in your neighborhood?
- Does the surrounding soil show signs of new settlement or erosion?
- Have you noticed new alignment problems with doors or windows in your house?
- Have floors or other surfaces in your home become uneven indicating possible foundation trouble
- Are all the local water mains and sewer lines free of cracks and leaks? (not sure that the average homeowner would able to find this out)
While none of these factors should be a cause for alarm regarding sinkholes by themselves, seeing a number of them persistently, especially in more than one home on your block, could be a sign of deeper problems. It’s a good idea to have a qualified technician check your property and enlist the help of a Geotechnical Engineer. Issues like these can usually be easily and affordably prevented or repaired with a wide array of new foundation technologies.
In cases where the trouble is found to be connected to sinkhole risks, there are still practical things that can be done to protect your home. Pilings can be added between existing foundations and deeper, more stable rock layers below. Voids can be filled with concrete or slurry mixtures that can restore the structural integrity of the surrounding soil.
There is reason to be optimistic. Although no one can predict where the next sinkhole is going to happen, we know a lot about what triggers them. Every homeowner who lives in one of these regions should be aware of the warning signs and check their property on a regular basis. On a much larger scale, we hope that the rising awareness of sinkholes will prompt some positive new policy changes. Responsible land and water use is an issue that impacts the quality of life for everyone.