Sinkholes in Florida
Sinkholes. All Floridians are scared of them, but what are they? Sinkholes are an area of ground with a depression or hole caused by some form of collapse of the surface layer. Many things can cause them, but usually a chemical dissolution of rock, soil, and other otherwise supporting subsurface elements. They vary drastically in size from small to massive holes, which can swallow entire properties. Although common, they are classified as a geologic hazard and can damage entire buildings, yards, lots, etc. The sudden destruction from sinkhole events can result in millions of dollars of repair costs / rebuilt costs and even threaten entire communities by damaging water supply sources or other valuable infrastructure pieces.
Where are these sinkholes most common? Sinkholes are present in geographies throughout most of the world. They are present in every single state in the United States. However, sinkholes are most common in areas where the rock below the land surface is a form of rock that naturally dissolves when groundwater circulates through it. Examples of this type of rock include carbonate rock, limestone, salt beds, and other similar types.
Map of Karst formations in the United States. Source: PBS
Unfortunately, the geography of the southeast United States sees areas with the highest concentrations of below ground surface elements that create sinkholes. As a result, we see as many sinkholes as any other part of the world. In particular, in Florida, sinkholes are unfortunately extremely common. Many of the areas below the state’s surfaces contain large voids in cavities in bedrock formations of areas such as limestone. With groundwater flow evident and close to Florida’s surface, this slightly acidic groundwater slowly dissolves away the bedrock. It creates these cavities and caves over many years.
Sinkholes explained. Source: UK Daily Mail Website.
Eventually, the dissolved area is large enough that the ground ceiling above it (which is the aboveground surface) can no longer support the large cavity’s weight, resulting in a collapse of the earth and creating a sinkhole. Well drilling data provided by Florida’s Department of Environmental Protection suggests these caverns are present and very common throughout the state’s entirety of underlying bedrock. However, the cavities present themselves in substantial differences in size and depth. Some are very large and others very small. Florida does not contain a database showing all of the sinkholes, as this would be extremely difficult to track. However, the Florida Geological Survey does maintain a database of “Report Subsidence Incidents,” which includes all incidents reported by observers. Most reported incidents tend to cluster in areas with larger populations as they are more commonly seen and experienced. However, more rural locations are present in the reports.
Many ask if any area in Florida is safe from sinkholes. No location is 100% safe. However, this reality is not exclusive to Florida. Soils and underground elements throughout the world are susceptible to sinkholes. The Southeast (and Florida in particular) see areas with much higher concentrations of the factors which contribute to these incidents. Therefore their percentages of the likelihood for the occurrence of these events are significantly larger. Although natural underground elements are the largest contributor to sinkholes, man is also increasingly contributing to these disasters. Modern communities have led to the creation of modern infrastructure. Modern infrastructure in dense areas includes countless miles of underground utilities for water, sewer, and other critical infrastructure pieces to support the growing population above it. As these populations grow, so does the infrastructure. It will grow in place, be used more in place, and expand geographically as suburban expansion continues. With this continued growth comes new building, rebuilding, and constant maintenance. With so many countless miles of infrastructure in place, tracking leaks large and small is more and more difficult. The small leaks are often the most challenging as they are challenging to track yet cause the most damage over time by going undetected. Leaks, aging utilities, or poor installation can cause issues that affect the ground below it through a consistent build-up of precipitation over time, creating undetected water droplets, leading to holes, which lead to eventual cavern build-ups, and under the right circumstances, collapses.
Miles and miles of pipe underground are tough to monitor. Materials age overtime at different variations depending upon their surrounding conditions – also making this difficult to monitor. Additional factors include road work and work to existing infrastructure pieces, which often unintentionally damage existing infrastructure without those at the surface knowing. As populations expand, they tend to move further away from population centers into more challenging geographies where karst is present, increasing the likelihood for these issues. As populations grow and expand, challenging properties become more attractive for people who want to live within a specific school district or in a desirable zip code. Therefore properties with underlying ground issues are developed and built on, despite their risks. These issues and potential issues are nothing new and will continue to be an issue moving forward as the human world grows and expands.
Almost the entire state of Florida is a Karst region – karst refers to landforms that develop due to the dissolving away (over geologic time) of geologic materials near the surface. In most cases, this material is limestone. Technically the entire state is underlain by these carbonate rocks. Therefore sinkholes can technically form anywhere; however, there are certain regions where sinkhole risks are much higher and other regions where the risks are considerably lower. The areas with the most extensive presence of sinkhole activities are those where limestone is close to the surface, areas with deeper limestone, and areas with specific water table elevation qualities. The only way to be 100% sure you are not susceptible to sinkhole activity is to avoid purchasing land in a karst region, meaning you do not buy property in the state of Florida. That said, there are preventative measures you can take. By hiring experts, you can survey your site through borings, geologic sites, and visual walks. These inspections provide you with professional reporting showing you whether or not any sinkholes are present, soon to be present, or possibly present in the future.
Signs of Sinkholes
A few other commons signs for consuming sinkholes are below:
- General Ground Depression
Before a sinkhole forms, you may notice a dip in the ground relative to the land around it. Sometimes this can blend in with surroundings and be challenging to detect for untrained eyes or a lack of familiarity with a familiar property.
- Circular Depression in the Ground
Prior to collapsing into the open cavern below, creating a sinkhole, the ground above often shows more apparent signs of an impending collapse through a small or large depression/dip into the ground. These depressions tend to be circular, a more obvious sign of what is to come.
- Foundation Settling
Foundation settling can be a standard item indicative of regular local activity, or it can be a convenient warning sign to a much larger incoming issue such as a sinkhole. Cracking in your foundation or a drop in portions of the property (including an entire structure) can be a sign of a significant issue. At this point, professionals should be sought immediately to confirm if a property is still structurally safe. If need be, geologic tests and soil sampling can confirm the safety level of the property.
- Creation of a Circular Puddle
If a circular shaped area holding water shows up suddenly, there is a good chance it is a sinkhole itself or is about to give way to a sinkhole. Sometimes these puddles can look more like a pond or a lake than a puddle.
- Pavement Cracks
Cracks in paved areas and roads can be a sign that your asphalt may be old or a sign of a temperature change. These same cracks can also signify a much larger below ground issue, such as the full or partial upcoming collapsing of ground into a cavern below, creating a sinkhole.
- Well Water Level Change
Despite modern infrastructure developments, tens of thousands of properties in the United States are still on well water, and many in very dense, populated areas. Therefore, wells and their water levels can be significantly informative of the state of below-ground conditions. When sinkholes open, they are often the result of water moving in increments or large amounts. When below-ground caverns open and expand; usually, water table levels change significantly in the area near these caverns. With wells accessing deep below groundwater, they are an excellent indicator for below-ground conditions.
- Rain Water Disappearance
Rainwater can sometimes be seen quickly disappearing in large amounts into a small opening. This disappearing water is an obvious sign of a large void below the surface where this water is running. This is almost always the sign of some level of sinkhole or below ground depression.
These days professional sinkhole analysis is critically important. To keep your family safe and your investment safe from a sudden tragic impact, you should take these necessary upfront steps. The small upfront cost will be a fraction of the long term negative impact of a sinkhole. In addition, the state has reduced its investment in preventative measures. In the early 1990s, the Florida Legislature discontinued funding for the Florida Sinkhole Research Institute (or “FSRI”). The research institute’s work is still present in other organizations, and other institutes such as universities have worked to continue their work, although not as effectively.
By the time you read this, you may already own property or have built your house. If this is your situation, you should still conduct these same inspections. By having an informed understanding of the land, your home is built on, you may be able to avoid an unforeseen catastrophe. But what if you already suspect you have a sinkhole? The hole should be immediately cordoned off and clearly marked, so people avoid it. Regardless of whether or not the suspected sinkhole is in a public or trafficked area, you can ensure the safety of anyone that might come across it by marking it off. Contact your local law enforcement officials immediately to report the hazard. If the sinkhole is located in a public area, call the appropriate authorities as well. For example, if the sinkhole is located on a road, contact your local city or county roads department to prepare to do the work and cordon off the area. Also, use common sense. If life and property are in immediate danger, call 911 and vacate the area. Make sure you contact your insurance provider.
Fortunately, few sinkholes are major issues. In fact, most are minor, requiring only filling with clean sand or soil. That said, always be careful. If you see a neighboring property of yours has a sinkhole, take the same precautions. Most of the bedrock underlying the state is honeycombed with cavities of varying size. Most of these will not collapse. However, a quick inspection of your property is essential to be safe.