Don’t Get Sunk: What To Know About Florida Sinkholes

Florida is known for its stunning beaches, theme parks, and interesting people, but it’s also renowned for something less picturesque but equally fascinating – sinkholes. These natural phenomena have garnered global attention due to their potential to swallow whole homes!

Reading that can be nerve-wracking, especially when planning to move to Florida. You likely accounted for the hurricane and flood risk, but now knowing the ground can give away under your home? This article aims to shed light on the science behind sinkholes, why they occur in Florida, and the measures taken to mitigate their impact on local communities and your home. 

What is a sinkhole?

Sinkholes are more common than you think. It’s a depression or hole in the ground caused when the surface collapses into an underground void. These vary from small pits to massive craters that take out highways, cars, and, yes, entire buildings. 

A sinkhole forms through a process known as “subsidence.” It’s the gradual dissolution of a soluble rock, like limestone, by acidic groundwater over centuries. When the rock can no longer support the weight above, it gives way, and voila! A sinkhole suddenly appears!

In Florida, sinkholes are often caused by the state’s underground limestone and dolomite layer. Over time, acidic water dissolves the limestone, creating voids that eventually cause the surface layer to cave in.

But Florida isn’t alone in having sinkholes; they are all across the US! Find them in Kentucky–Mammoth Cave’s natural entrances are sinkholes–Missouri, Texas, Ohio, Arizona…pretty much every state has current or past sinkhole activity, even North Dakota!

Why are sinkholes common in Florida? 

Florida is a leading state for sinkholes and sinkhole-related damage. It has a high number of sinkholes due to its geological makeup. The underground porous limestone and dolomite are easily dissolved by groundwater. Seeing how Florida is a low-lying state, its groundwater table­–the Florida aquifer–can be as shallow as 100 feet deep, and it averages 54 inches of rain a year, the conditions are ripe for sinkholes.

Usually the natural surface layer can hold up the sediment and rocks above it. Over time, rainwater, which is naturally acidic due to carbon dioxide, seeps into the ground, slowly eroding the limestone and creating hollow spaces. A high rain event–say a slow-moving tropical storm–can speed up the dissolving process.

When the water level in the aquifer drops, it creates an empty space. The surface layer can no longer hold the weight above. And if a home or structure is on the surface when it collapses, it can cause significant damage.

No agency tracks the cost of sinkhole damage, but the US Geological Survey estimates it runs about $300 million per year nationwide. One Florida engineering firm estimated the start of sinkhole damage repair to a home at $10,000 for a small sinkhole, only a few feet wide. The repair cost will depend on the sinkhole’s size, how it is being formed, and the square footage that is being impacted. Deaths are rare but have been known to happen in sudden collapse events.

Humans factor in sinkhole development

While sinkholes are a natural process, human activities can and do exacerbate their creation. Overdrawing groundwater, for instance, can lead to increased soil compaction and a higher risk of subsidence. This happened in 2010 when 110 sinkholes appeared in one area after a freeze event. Farmers pumped water to protect their plants, but the sudden high volume of removed water caused the sinkholes to appear. 

Excessive pumping of groundwater, construction practices, and changes in land use can all contribute to sinkhole formation. That’s an issue in Florida, where the increasing population and drawing down of the Florida aquifer to water golf courses and support the influx of people contribute to more sinkhole activity.

Types of sinkholes

Sinkholes are categorized into three main types: dissolution, cover-subsidence, and cover-collapse sinkholes.

• Dissolution sinkholes form gradually as the rock dissolves, causing the ground to sink over time and often creating ponds or wetlands. For those paying attention to changes in their ground level or settling around the home, these are usually detectable in time, and steps can be taken to mitigate damage.
• In cover-subsidence sinkholes, the overlying sediments–usually sand–gradually settle into the underground cavity, resulting in a gentle depression on the surface. The collapse is less dramatic.
• Cover-collapse sinkholes are the most dramatic and potentially destructive type. These sinkholes form suddenly when the surface layer collapses into the cavity below. These appear after Florida experiences a drought followed by unusually heavy rains or a dramatic draw-down of the aquifer.

Where sinkholes crop up in Florida

There’s some mixed news if you plan to buy a Florida home. The sinkhole risk is concentrated in particular regions of the state. Low-lying South Florida, from Naples across the Everglades to Miami, has the lowest risk, as does the Pensacola metro.  

The highest risk of sinkhole or “subsidence” activity is in a stretch of Florida from about Tampa Bay northward, particularly along the I-75 corridor. Central Florida’s slightly higher elevation, dense limestone underlayer, and deep Florida aquifer make it the most prone to sinkholes. The concentration of freshwater springs is a sign of its predilection to ground collapses. The cities of concern include Orlando, Ocala, Crystal River, High Springs, Tallahassee, and Suwannee. See a sinkhole map below. 

What are the warning signs of a sinkhole? 

If you’re looking to buy a property in Florida, note some red flags to look out for when you or your real estate agent tour the home. This is especially true if you’re looking to buy in central Florida. For instance, large trees leaning, sloping floors, and wall cracks can be signs of a sinkhole. If doors and windows no longer open and close correctly or you see depressions on the property, you must consult a professional to investigate.

Be aware your home inspector is not required to or is typically qualified to conduct sinkhole testing as part of their home inspection; a certified geologist must do that. 

• Doors or windows start to jam or not close
• Cracks in walls, especially where walls meet ceilings
• Cracks in vinyl or tile over a concrete floor
• Cracks in interior joints
• Slanted floors
• Sloping stairs
• Wet Crawl Spaces
• Cloud well water
• Depressions in the yard
• Confirmed sinkhole activity nearby
• Slumping trees, fence posts, or other objects

What to know about sinkhole coverage in homeowner’s insurance? 

Homeowners insurance in Florida doesn’t typically include sinkhole damage; you’ll have to purchase sinkhole coverage with insurance providers separately to cover the catastrophic damage these can cause. However, your home insurer will likely require inspection and testing before writing the policy.

Florida law does require insurers to cover “Catastrophic Ground Cover Collapse,” which includes a sudden ground collapse that results in structural damage or the structure being condemned. It will not cover the repairs from a gradual land sinking like in a dissolution sinkhole.

Frequently Asked Questions About Sinkholes in Florida

What part of Florida is safe from sinkholes?

Parts of Florida are generally considered safer from sinkholes, with the least risk in the southeastern region, including Miami-Dade, Broward, and Palm Beach counties. This area has a lower prevalence of limestone formations that contribute to sinkhole development. The Florida Geological Survey indicates that the central part of the state, specifically the “Sinkhole Alley” area, which encompasses Pasco County, Hernando County, and Hillsborough County, faces the highest sinkhole risk due to its geological structure.

What is the sinkhole alley in Florida?

“Sinkhole Alley” is the name given to a part of region in Central Florida known for its high frequency of true sinkholes. It includes parts of Pasco, Hernando, and Hillsborough counties, where the limestone bedrock is susceptible to erosion, leading to ground collapses.

The region’s combination of sandy soil and the movement of water through porous carbonate rock like limestone creates favorable conditions for sinkhole formation. Factors such as heavy rainfall, construction, and groundwater pumping can further accelerate sinkhole development in this area of the Sunshine State.

What towns are in the Sinkhole Alley in Florida?

“Sinkhole Alley” in Florida encompasses parts of Pasco, Hernando, and Hillsborough counties, regions particularly susceptible to sinkholes due to their geological composition. Notable towns and cities within this area include:

• Pasco County: New Port Richey, Dade City, Zephyrhills
• Hernando County: Brooksville, Spring Hill, Weeki Wachee
• Hillsborough County: Tampa, Plant City, Brandon

These counties and cities experience a higher frequency of subsidence incidents. Factors such as heavy rainfall, groundwater extraction, and construction activities can exacerbate the formation of sinkholes in these regions.

How do they fix sinkholes in Florida?

In Florida, fixing sinkholes generally involves a few specialized techniques, each tailored to the severity and type of sinkhole. Here’s an overview of the most common methods:

1. Grouting: This process involves injecting a mixture of cement, sand, and other compounds into the ground to fill the voids and stabilize the soil. For smaller sinkholes, pressure grouting may be used to fill underground spaces directly.Underpinning: For larger or more severe sinkholes near buildings, underpinning is often used. Steel piers are driven deep into the stable bedrock to support and stabilize the structure. This method is common for homes or buildings affected by subsidence.Compaction Grouting: This method involves injecting a thicker grout mixture to compact loose soil and increase stability. It’s commonly used when the sinkhole is not large enough to cause collapse but requires stabilization.Excavation and Repair: For shallow sinkholes, workers may excavate the hole, fill it with a stable material like gravel or sand, and then compact it before adding soil and reseeding the area.

   Sinkhole repairs in Florida are typically done by licensed geotechnical engineers and contractors who assess the conditions to determine the best approach for stabilization.

What is the sinkhole law in Florida?

Sinkhole laws in the state of Florida are covered under the Florida Statutes Chapter 627, which focuses on property insurance for sinkhole damage. The law requires insurance companies to provide catastrophic ground cover collapse coverage as part of standard homeowners’ policies, which covers structural damage due to sinkholes. But not all sinkhole damage qualifies for this coverage; the damage must meet specific criteria, such as structural instability and uninhabitability.

For additional coverage, homeowners can purchase optional sinkhole insurance, which provides more comprehensive protection and covers damage that may not meet the threshold for catastrophic coverage. The law also outlines procedures for insurance claims, including requiring insurers to conduct geological testing and provide repair options for verified sinkhole activity.

Are there always warning signs before a sinkhole?

Not all sinkholes show warning signs, but certain indicators can suggest some level of ground instability:

1. Cracks in the Ground: Small cracks in the soil or pavement can be early indicators. If cracks widen over time, they may signal common signs a developing sinkhole beneath the surface.
2. Structural Cracks: Cracks in walls, floors, or foundations, especially those that appear suddenly or grow quickly, can indicate that the ground is shifting.
3. Windows and Doors Not Closing Properly: As the foundation shifts, doors and windows may become misaligned, sticking or not closing properly.
4. Sagging or Depressed Areas: Ground depressions, such as small dips or areas where the soil appears sunken, could indicate a void forming below.
5. Changes in Water Drainage: Unusual pooling or areas where water collects may result from shifting ground that affects drainage patterns.
6. Sinkhole-Like Pits: If smaller pits form in yards or fields as the soil settles, it can be an early sign of a developing sinkhole.

Take any of these signs seriously, particularly in areas prone to sinkholes. Local government offices or a geotechnical engineer can offer further inspection if needed.

What is the average cost of sinkhole insurance in Florida?

You can expect sinkhole insurance in Florida to average between $2,000 and $4,000 annually. It will greatly depend on factors such as your location and the property value. Expect higher premiums in sinkhole-prone areas, with sinkhole claims often surpassing $140,000, making insurance a good investment for homeowners at risk of a sinkhole situation.

How much does it cost to fix a sinkhole in Florida?

Repairing a sinkhole in Florida can be a major investment, with costs varying based on the size and severity of the sinkhole. For minor sinkholes causing minimal structural damage, repairs may range from $10,000 to $15,000. However, sinkhole occurrences that cause more damage can require repairs costing between $20,000 and $100,000 and even more

The primary methods for solution sinkhole include:

• Grouting: Injecting grout into the ground to fill voids and stabilize the soil.
• Underpinning: Installing steel piers to support and stabilize the foundation.

Do pools cause sinkholes?

Swimming pools themselves do not directly cause sinkholes, but they can contribute to sinkhole formation in with sinkhole susceptibility. Large pools, including Olympic-sized swimming pools, require substantial water, which can lead to increased water movement through the soil. If the pool leaks or if groundwater pumping occurs to maintain water levels, the surrounding soil may erode more quickly, weakening the limestone bedrock beneath and potentially triggering sinkhole incidences.

Protecting your Florida home

Understanding the science behind sinkholes, their classifications, and the geological factors that make Florida susceptible to their formation is crucial for residents and policymakers. Don’t let sinkholes be a deal-breaker in your Florida home search. Consult with realtors and professionals to ensure you’re making an informed decision.