A new crack in a slab or block wall is unsettling, and in Central Florida the word "sinkhole" comes up quickly. Usually there is a more ordinary explanation. Cracks have many causes, and the state's own geologists list several common look-alikes before anyone should conclude a sinkhole is involved.
This article explains the two kinds of sinkholes the Florida Geological Survey (FGS) describes for this region, why sandy soils mostly produce settlement rather than sinkholes, and how a professional engineer or professional geologist tells the two apart.
Two kinds of sinkholes, in the FGS's words
The FGS describes two main types relevant to Central Florida:
- Cover-subsidence sinkholes "are located where thick permeable sediments cover the limestone." The surface tends to sag gradually.
- Cover-collapse sinkholes "occur where sediments overlying the void in the rock suddenly collapse."
A 1985 state map (FGS Map Series 110, Sinclair and Stewart) sorts Florida into zones by cover type. Where the cover is "mainly of incohesive and permeable sand," it says sinkholes "are few, shallow, of small diameter and develop gradually." Where the cover is "cohesive clayey sediments of low permeability," sinkholes "are most numerous, of varying size and develop abruptly." The map is regional, at roughly 1:2 million scale, and Orange, Seminole, Osceola and Lake counties each include more than one zone, so it cannot describe a single street or lot.
What settlement means
Settlement means the soil under part of a slab or footing compresses or shifts, and the concrete above follows it. It is common, and it has many causes that have nothing to do with limestone. When the FGS explains why a reported depression is often not a true sinkhole, it lists subsurface "organic layers which compress as water is removed, collapsed or broken sewer and drain pipes or broken septic tanks, improperly compacted soil after excavation work, and even buried trash, logs and other debris."
Florida law draws the same line in its insurance statute: "Damage consisting merely of the settling or cracking of a foundation, structure, or building does not constitute a loss resulting from a catastrophic ground cover collapse" (§627.706(2)(a)). And to count as "sinkhole activity," settlement must result from "movement or raveling of soils … into subterranean voids created by the effect of water on a limestone or similar rock formation" (§627.706(2)(i)). Cracking alone does not show that.
A 2010 Florida Senate staff report described a $16,574 sinkhole test that found improper construction, not a sinkhole.
What Orlando-area soils actually are
Mostly sand, with negligible shrink-swell
Orlando-area soils are mostly sands with negligible shrink-swell, according to the USDA Natural Resources Conservation Service soil survey (SSURGO). The most widespread series include Smyrna, Candler, Tavares, Myakka and Basinger. Candler, a deep sand on the uplands, tests at roughly 1 to 1.4 percent clay with a linear extensibility of 0, which means it essentially does not swell or shrink with moisture.
The soils differ in drainage. Candler is "excessively drained," while Smyrna, found on flatwoods, is poorly drained, with "the water table … at depths of less than 18 inches for 1 to 4 months in most years," according to its official series description. Water moving through sand near a slab edge can wash soil away, which is one reason gutters, downspouts and grading matter here. The drainage and grading page covers that work.
Muck pockets
Organic soils, called muck, are the main exception. They cover roughly 6 to 7 percent of Orange, Seminole and Osceola and about 13 percent of Lake (NRCS SSURGO). Samsula muck, for example, has a surface layer about 75 percent organic matter that formed in swamps and drainageways. Organic layers compress as they lose water, so a house built over a buried muck pocket, or over poorly compacted fill, can settle unevenly. These are county-wide figures; nothing in the soil survey says which subdivision sits on which soil. Our article on sand, muck and Orlando foundations goes further.
What the reported incidents show, and what they do not
The FGS keeps a statewide database of subsidence incident reports. As of October 19, 2026, it held 232 reported subsidence incidents in Orange County, 172 in Seminole, 178 in Lake and 16 in Osceola, out of 4,457 statewide records. Those numbers need context:
- The reports are voluntary. In the FGS's words, "the majority of the incidents have not been field-checked and the cause of subsidence is not verified."
- A reported depression is "commonly" not verified by a licensed professional geologist as a true sinkhole, which is why the FGS calls each one a subsidence incident.
- Many older records are located only to a survey section, so counts for individual places are approximate.
The insurance claims data tells a similar story about scale. A Florida Senate staff report (Interim Report 2011-104) found that Orange County accounted for 2.2 percent of the state's 2006–2009 sinkhole claims, while Hernando, Pasco and Hillsborough counties accounted for over 66 percent.
Large events are rare but documented. The Winter Park sinkhole of May 8, 1981 was about 300 feet across, with a visible depth of about 80 feet, according to the U.S. Geological Survey.
Weather and timing
The FGS says "sinkhole activity is greatest when there have been drought conditions for some period of time," and lists drought, heavy rainfall and heavy groundwater pumping among the triggers. Central Florida sees both extremes. Orlando International Airport's normal year brings 51.45 inches of rain, about 57 percent of it from June through September (NOAA 1991–2020 normals). Hurricane Ian dropped 13.2 inches there on September 28–29, 2022, according to the National Hurricane Center, and 2026 had one of the driest starts on record.
How a professional tells settlement from a sinkhole
Diagnosing the cause of foundation movement is engineering under Florida's chapter 471, and only a Florida-licensed professional engineer (PE) may do it. For sinkhole questions specifically, Florida's insurance statutes require testing by a professional engineer or a professional geologist (§627.7072). The FGS adds that licensed home inspectors and insurance adjusters "are not trained nor qualified to determine if there is a sinkhole," and that "the expertise of a licensed professional engineer is required to determine if a structure is structurally safe."
A sinkhole investigation by a PE or geologist can include:
- A floor-elevation survey to map where the slab is high and low, and whether the pattern looks like edge settlement or a localized low area.
- Ground-penetrating radar to look for disturbed soil or anomalies below the surface.
- Standard penetration test (SPT) borings to sample soil layers and find loose or raveling zones and the depth to firm material.
- A review of drainage, plumbing and construction history, since broken pipes and poor compaction appear on the FGS list of look-alikes.
A contractor's free evaluation and quote is useful for pricing a repair, but it is a sales estimate, not an engineering opinion. The foundation and sinkhole inspection page compares the kinds of reports.
No agency inspects sinkholes for homeowners
The FGS is direct about this: "No, there is no agency with responsibility or authority for sinkhole inspections in Florida." The FGS does run a Sinkhole Helpline (850-245-2118) for general questions. If a hole opens in a yard, its advice is to "mark and secure the hole" and "do not put water into the hole."
For insurance questions, ask your insurer what your policy covers; our article on Florida sinkhole insurance law explains what the statutes say. This is general information, not legal or insurance advice.
When repair quotes make sense
Once the cause is known, the repair usually follows from it: drainage fixes and crack repair for minor settlement, foam lifting or piers for a slab that has dropped, and grouting or underpinning when an engineer finds sinkhole activity. See slab foundation repair and sinkhole and subsidence repair for how that work is done. Orlando FL Foundation Repair connects Orlando-area homeowners with independent Florida-licensed contractors for free, no-obligation foundation repair quotes; the contractor you choose quotes, contracts and does the work. Request free quotes when you are ready.
Frequently asked questions
How can I tell if a crack is settlement or a sinkhole?
You usually cannot tell from the crack alone. The Florida Geological Survey lists many look-alikes, including compressing organic layers, broken pipes and poorly compacted fill. Diagnosing the cause is engineering, so a Florida-licensed professional engineer, or a professional geologist for sinkhole testing, uses floor-elevation surveys, ground-penetrating radar and soil borings to find out.
Do Orlando-area soils shrink and swell?
Mostly no. USDA soil survey data show Orlando-area soils are mostly sands, such as Smyrna, Candler and Tavares, with negligible shrink-swell. The local settlement drivers are washout at slab edges, poorly compacted fill and organic muck, which covers roughly 6 to 7 percent of Orange, Seminole and Osceola and about 13 percent of Lake.
Does any Florida agency inspect sinkholes for homeowners?
No. The Florida Geological Survey says there is no agency with responsibility or authority for sinkhole inspections in Florida. It runs a Sinkhole Helpline at 850-245-2118 for general questions. Whether a home has sinkhole activity is determined by a professional engineer or professional geologist hired to investigate the property.