Research Florida Sinkhole – Avoid Buying a Sinkhole House

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Have you made the decision to become a snowbird?  To trade in your snow shovel for a beach umbrella?  To give up skiing and take up boating?  Or have you just made the dramatic choice between two opposing weather patterns and you are now looking for a new permanent home, or at least a home that gets you out of the cold during the winter months?

Whatever your goal, periodic or permanent, looking for a home in any new location requires that you become knowledgeable about your environment in very different ways.  Up north, in older communities, you need to think about lead water pipes, sump pumps, leaky basements, and, of course how many times a year you’ll need new tires from driving over the latest crop of potholes.

If you are thinking about living in the southeast of the US, you’ll be hard pressed to find a basement unless you build your own home.  You won’t need snow tires any more, but you may want to trade your black or navy blue car in for a white or light-colored vehicle to fend off all the heat that sunshine brings.

But most Floridians say, “Wow, another sunny day in paradise!”   That will certainly be true if you do your homework before you invest in your new home.  You won’t be looking at public transportation to big cities, older shrubs, trees, and “cathedral” streets where the branches on either side of the street meet each other in the middle, and all the man-made risks you encounter up north.

Instead, you’ll need to investigate this earth we all call home more carefully than anything we have built on it.  We don’t often think about the fact that the earth itself is not really a solid mass.  Geologists know that there are numerous strata below the surface of the earth.  Some of the strata are solid rock covered by soil and numerous types of stone.  But some strata consist of gases and liquids and varieties of softer and harder stone.

When the equilibrium among these types of materials is disturbed, the result can be upheavals and depressions that swallow up houses, cars, trucks and people.  You’ve heard of major sinkholes swallowing up blocks and blocks of structures, but you don’t know where the unstable land is and you probably won’t find a seller or real estate company that can put up a sign that says: “Buyer Beware!  Future Sinkhole on this Property,” or even, “Remediated Sinkhole Here.  Look out for the next one!”

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The prevalent topography in northern and central Florida consists of sand and clay covering limestone.  When rain and circulating groundwater soften the limestone, cavities and crevices are created, and the resultant landscape is called karst topography, which consists of caves, sinkholes and subsidences.

Pressure created by buildings, roads, and traffic add to the subterranean movement of water and the dissolution of limestone to cause the weak crust to fail, creating these sinkholes and subsidences.

So how do you find out which properties to stay away from?  And how can you protect your property and avoid losing your investment and your home?   The first step is to begin to understand the practicality of dealing with this geological phenomenon.

Step One –Where have sinkholes and subsidences occurred?

Pull up the “U.S. Karst Map” on the Internet.  This article from the Journal of Cave and Karst Studies (April 2002, p. 45-50), includes the map of karst areas in the U.S. published by the American Geological Institute (AGI).  You will note that the state of Florida is the largest expanse of land in the U.S. which is subject to depressions due to the dissolution of the underlying bedrock.

US Karst Map


Step Two – How is Florida impacted?

The Florida Department of Environmental Protection (FDEP) is the most reliable source of information about sinkholes in Florida, but even its information is not foolproof.  From the maps available you can identify counties with historically more or less sinkhole activity.  The FDEP offers a useful document, “Sinkhole FAQ” to answer 24 important questions and help you understand the basics about sinkholes.

“Reported Sinkholes Since 1954” (1954- 2008, information provided by Florida Geological Survey Map Series No. 110) and “Florida’s Sinkholes” (Florida Geological Survey Poster No. 11) are maps which provide the general location of sinkholes from a 30,000-mile view of the entire state.  (Both of these maps can be Googled)

Now, you have a general idea of areas to avoid, or, if you must relocate to one of the sinkhole-concentrated areas, the care you will have to exercise in your home search.

Step Three – Where in Florida have the most sinkholes occurred?

Sinkholes by County” is published by the Florida Center for Instructional Technology (FCIT).  These maps cover the same period (1954 – 2008), but list each event and location by month, year, longitude and latitude.

The eight most “productive” counties, Hillsborough, Marion, Pasco, Polk, Hernando, Citrus, Orange, and Seminole, each with 192 to 348, totaling 1894 sinkholes or just under 70% of the total Florida sinkholes, occupy the central area of the state from the west coast to the east coast.

The next eight counties, each with 55 to 126 sinkholes, totaling 628, amount to about 23% of the total, with an additional 13 counties contributing 198 sinkholes, or less than 7% of total for the state.

Finally, that leaves 17 counties with no history of any sinkhole events and another 19 with one to four sinkhole events, not a significant figure over a 54-year period.

Here is a more up to date Sinkholes by County data based on database.

Step Four – What is the specific sinkhole impact on the county of interest?

Some of the counties have independent records of sinkholes and additional information may be available on their websites.  The eight “productive” counties listed above have their own tracking systems.  In addition, three of the counties in the next list, Suwannee, Pinellas, and Lake, make information available on their county websites.

If you are determined to live in one of these eleven counties, visiting the websites, talking to environmental specialists within the county governments, and reviewing the relevant Florida State Water Management District websites or offices may give you area information helpful to your decision process.  From this site, the Florida DEP “Subsidence Incident Reports” directory and maps can be accessed, and a guide for use of the “Subsidence Incident Reports Map” will direct you to additional information.

Step Five – Besides residential and commercial properties, how have sinkholes impacted the county?

Of the five Water Management Districts, two cover much of the sinkhole-concentrated areas.  Specifically, Suwannee County is within the Suwanee River Water Management District, and Lake County, Orange County, and most of Marion County are in the St. John’s River Water Management District (for example, the Suwannee River Water Management site: and the St. Johns River Water Management site).

If at this point in your quest, you have identified a county and perhaps a specific area within the county, you may want to investigate the Surface Water Improvement and Management reports (SWIM Reports), issued by the Florida Water Management Districts

The SWIM Reports cover lakes, watersheds, and creeks affected by a variety of natural and unnatural events, where the local demand for better water management have resulted in the allocation of funds for that improvement.  To locate the SWIM Reports, do a search and a list of the available reports will take you next to a specific report.

A chance review of one SWIM Report revealed an area of 15 acres in Walkulla County where sinkholes beneath Alligator Lake at times drain the lake dry and dramatically affect the local ecosystem.  The tax consequences for the restoration of the lakebed which were begun in 1988 may continue to have an impact on residential home values and expenses for decades.

Step Six – What other sources of information are there?

Insurance industry reports can be very helpful.  The Insurance Journal has reported that sinkhole insurance claims in Florida are rising.   A survey of 211 insurance companies reported to The Office of Insurance Regulation (OIR that claims costs totaled over $1.4 billion between 2006 and 2010 (about $1.2 billion paid out and another $245 million in corporate expenses to investigate the claims, with a total of almost 25,000 claims, both settled and open, filed in those same years.

The data included almost 9,000 open claims and almost 16,000 closed claims for this period, of which 54% were for Structural Loss, 27% for Land Loss, and 12% for Engineering Expenses.

But here is the disconnect.  FDEP reports just under 3,000 sinkholes in Florida in a 54-year period.  But, FLOIR reports over eight times that many insurance claims, over the five years between 2006 and 2010, for a variety of sinkhole-type events, including “catastrophic ground cover collapse,” according to the Report on Review of the 2010 Sinkhole Data Call of November 8, 2010.

The reported insurance claims arise from “collapse sinkholes,” where the result is a gaping hole in the land, from “subsidence sinkholes,” where the top layer of the soil is thin and a depression in the ground is evident, and which are usually only a few feet in diameter and depth and can eventually be filled with a spring or pond.  The third phenomenon is “clay shrinkage,” where seasonal and annual precipitation cause clay to expand or shrink and result in the ground shifting under buildings.  Clay activity tests are complex and expensive.

The OIR reports that 57% of claims paid were for subsidence sinkholes (average payout $140,000), 2.4% for clay shrinkage ($102,000), and only 1.1% for catastrophic ground cover collapse ($150,000).

Also of note, the incidence of subsidences and clay shrinkage are in the eleven “productive” counties, but also up and down the east and west coasts of Florida and sprinkled throughout counties not highlighted as high risk for sinkholes (see “Subsurface Geology and Sinkholes, State of FL” in the Insurance Journal, with the map produced by CDS Business Mapping, LLC, 02/2011).

Step Seven – How do I protect my property and my investment?

Making Florida your home means you are definitely relocating to an area fraught with sinkhole and subsidence risk.  You have found the perfect home and although the property seems not to have suffered a sinkhole event, you can’t be sure about the future.  Or maybe you are not 100% sure that the property hasn’t suffered even a small subsidence or clay shrinkage event.  There are a few things you still want to consider.

Is the current owner willing to give you written permission to obtain information from the insurance company which provided home coverage over the duration of his ownership?  You would want to review any claims filed by the owner and settled or denied by the company.

Was a geological study performed before the area was first developed?  What were the municipal restrictions at the time of the development? Is it typical for geological studies to be required or recommended before transfer of title in this area?

Which sinkhole remediation companies are active in the area?  Are they willing to share information regarding the area you are considering?  Are the sinkhole remediation solutions they use considered state of the art?  (Look into non-invasive polymer injection remediation used for concrete leveling and lifting, soil stabilization and infrastructure rehabilitation.)

And finally, make sure that the insurance carrier you are contemplating includes sinkhole risk coverage beyond catastrophic collapse, as well as reimbursement for temporary housing expenses for the time you and your family may have to live away from your home.

As we have traveled this journey, many readers may have taken a detour or chosen an entirely different route, opting for counties and areas with low sinkhole risk. If you are still with me, you are now better prepared for the possible consequences of your move to a higher risk area of Florida.  Risk management is a day-to-day responsibility each of us bears in one way or another.  Make sure to go into the financial and emotional decision of selecting where you and your family will live with your eyes open and knowing what could occur.  Have a great sunny day in Florida’s paradise knowing you have prepared well.


Guest Blogger C. D. Holmes is an experienced researcher, writer and editor in a variety of fields.  Her background as an international commercial banker and business consultant brought access to various industries – professional services, consumer goods, real estate, asset-based finance, textile and apparel, metals processing, and commodity trading.

The content in this blog is an overview provided for general information purposes only, and does not constitute professional advice. The author does not accept any liability arising from the use of the information provided here or from the omission of information.  

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