Sinkhole Risk in Jacksonville and Duval County

Jacksonville sits on Florida limestone like the rest of the state, but Duval County has only 16 subsidence reports in the state database, a small fraction of the counts in west central Florida.

The Florida Geological Survey answers the question of a safe area of Florida with no chance of sinkholes this way: Technically, no, because the whole state rests on carbonate rock (Florida Geological Survey, Sinkhole FAQ). The same answer says risk is considerably higher where limestone is close to the surface, or where deeper limestone combines with a water table and layering that favor collapse. Under Duval County the limestone is buried hundreds of feet down, according to the USGS figures below.

The state record reflects that. A query of the Florida subsidence incident layer on October 15, 2026 returned 16 reports for Duval County, compared with 618 for Hillsborough County and 489 for Marion County (FDEP Open Data, subsidence incident counts). Jacksonville's neighbors are lower still: 6 in Clay County, 5 in St. Johns County and 2 in Nassau County.

Those counts measure reporting, not certainty. The FGS says there was never a legal requirement that sinkhole occurrences or sinkhole insurance claims be entered, and that every incident was reported voluntarily (Florida Geological Survey, Subsidence Incident Reports). The counts therefore show what was reported to the state, not every hole that opened.

Under Jacksonville the Ocala Limestone, the top of the Floridan aquifer system, lies about 250 to 600 feet below sea level beneath an intermediate confining unit of lower permeability sediments.

A 2002 U.S. Geological Survey report on Duval County puts the top of the Floridan aquifer system at about 250 feet below sea level near Jacksonville Naval Air Station and about 600 feet below sea level in parts of central Duval County (USGS Open-File Report 02-426). Between that limestone and the shallow surficial aquifer sits the intermediate confining unit, beds of lower permeability sediments that confine the water in the Floridan aquifer system.

The limestone itself is old karst. The USGS describes the surface of the Upper Floridan under Duval County as a paleokarstic plain exhibiting erosional and collapse features that developed before the deposition of the overlying Hawthorn Group. Seismic surveys along the St. Johns River in northeastern Florida found buried collapse features in the Floridan rocks, and land based surveys found them in Duval and St. Johns counties (USGS). The USGS adds that collapse features can create conduits that provide a hydraulic connection between freshwater and deeper, more saline zones within the aquifer system.

The process that makes a sinkhole is the same statewide, Jacksonville included: slightly acidic rain water percolates through porous limestone, dissolves it over eons of time into underground voids, and collapse of the overlying sediments into those cavities produces sinkholes (Florida Geological Survey, Sinkholes).

The 16 Duval County records in the state subsidence database all show U, not Y, in the Verified Sinkhole field, and the newest dated record is July 4, 2026.

The Duval County query lists each record with its date, size and whether property damage was noted (FDEP Open Data, Duval County subsidence records). The July 4, 2026 entry lists a feature 20 feet long and 20 feet wide. The largest Duval entry is a May 1990 record with Mayport as the owner's city that lists a hole 100 feet long, 100 feet wide and 30 feet deep, with property damage marked. Several other Duval entries list holes 2 to 8 feet across.

The FGS is careful about what these records mean. A subsidence incident is a sunken spot that a licensed professional geologist has not confirmed as a true sinkhole, and the majority of records statewide have not been field checked (Florida Geological Survey), and none of the 16 Duval County records is marked as a verified sinkhole. Look-alike causes listed by the FGS include decomposing stumps or organic debris, collapsed or broken sewer and drain pipes, broken septic tanks, improperly compacted soil after excavation work and buried trash (Florida Geological Survey).

A hole in a Jacksonville street is reported to law enforcement if it is a hazard and to the city's Public Works Department at (904) 630-CITY (2489), while a hole on private property is the owner's responsibility.

For a street hole, the FGS says to cordon it off and mark it, report the hazard to local law enforcement and call the city or county road department (Florida Geological Survey, Sinkhole FAQ). In Jacksonville that is the Public Works Department, which handles roadway maintenance, at 214 N. Hogan Street, 10th Floor, which also runs the Jacksonville Stormwater Utility and takes requests and problem reports through 630-CITY (City of Jacksonville Public Works).

For a yard in Jacksonville or anywhere in Florida, the FGS advice is to fill small holes with clean sand or soil, never pour water in, mark the spot and keep children and pets away; if walls are cracking or sagging, the household should stay out and call its insurance adjuster at once (FGS). No Florida agency inspects private sinkholes: the FGS says there is no agency with responsibility or authority for sinkhole inspections in Florida. Its pages give two different pointers: for an assessment, contact a certified home inspector or foundation specialist, yet the same FAQ says licensed home inspectors and insurance adjustors are not trained nor qualified to determine sinkhole activity, which licensed professional geologists or engineers are trained to recognize. The FGS Sinkhole Helpline at 850-245-2118 answers sinkhole questions and gives verbal guidance, and the FGS encourages submittal of subsidence incident reports (Florida Geological Survey).

Every Florida property policy, including on a Jacksonville home, must cover a catastrophic ground cover collapse, but wider sinkhole loss coverage is optional and costs extra.

Section 627.706 of the Florida Statutes says every insurer authorized to transact property insurance in this state must provide coverage for a catastrophic ground cover collapse, and that includes insurers writing Jacksonville homes (Section 627.706, Florida Statutes). The bar is high: the law requires all four of an abrupt collapse of the ground cover, a sunken area in the ground cover clearly visible to the naked eye, structural damage to the covered building including the foundation, and the structure being condemned and ordered vacated by the government agency with that authority. Insurers that exclude sinkhole losses must tell policyholders in bold type that the policy covers a catastrophic ground cover collapse that results in the property being condemned and uninhabitable, and otherwise does not cover sinkhole losses.

Insurers must offer broader sinkhole loss coverage for an appropriate additional premium, and a residential policy on a Duval County home may carry a sinkhole deductible of 1, 2, 5 or 10 percent of the dwelling limit (Section 627.706). On a sale, the FGS notes that statute 627.7073 requires the seller to disclose only that a sinkhole claim was made against the property and paid by the insurer, and whether the money went to repairs (FGS, Sinkhole FAQ).

Jacksonville owners can report a new sunken spot so it enters the state record, and the county hazard plan named on JaxReady on October 15, 2026 was the 2020 edition.

The JaxReady Local Mitigation Strategy page says FEMA and the State of Florida approved the 2020 Duval County LMS and that the plan runs on a five year life cycle with periodic updates (JaxReady, Local Mitigation Strategy). The page says periodic updates may include revised hazard profiles and vulnerability assessments; on October 15, 2026 it still named the 2020 plan. The Duval Prepares advisory committee meets quarterly to review and add mitigation projects, and the Emergency Preparedness Division provides minutes of past meetings at [email protected] or 255-3110.

Statewide, the FGS says a majority of subsidence records now come from the State Watch Office, the clearinghouse for emergency response calls, whose reporting form county, city and state dispatchers fill out if they choose to; the second source is members of the public who submit the FGS subsidence incident report form (Florida Geological Survey, Subsidence Incident Reports). The Duval County query fields do not show which channel each Jacksonville record came from.