Florida Karst II

Karst of the Floridan Aquifer System

Karst features within the Floridan Aquifer System can be classified according to whether they recharge the aquifer, discharge from the aquifer, or conduct water through the aquifer. Karst features serving as recharge points to the Floridan Aquifer System are scattered throughout the semi-confined and unconfined aquifer, essentially one below every sinkhole. The vast majority are inaccessible. Most have small or sediment-filled openings to the surface. The potentiometric surface is not deep below the surface anywhere in Florida; therefore, most conduits are currently under phreatic conditions. Fluctuating sea-level positions clearly affect the potentiometric surface in portions of the unconfined Floridan Aquifer System. Evidence of lower water table periods comes in the form of speleothems in conduits beneath the present-day water table.

Figure 1. Simplified geology of Florida. Dark gray areas indicate where the Eocene and Oligocene carbonates (Suwanne Limestone, Ocala Limestone, and Avon Park Formation) of the Floridan Aquifer System are unconfined. Black areas delimit the surface exposure of Miocene siliciclastics (Hawthorn Formation).

Voids currently in the vadose zone indicate higher positions of the water table in the past. The highest densities of vadose karst features occur along the boundary between the confined and unconfined Floridan Aquifer along positive geographical features capped by Miocene siliciclastics such as the Brooksville Ridge, the Ocala Rise, and the Cody Scarp. Most explored vadose caves have no natural human-sized entrance. Instead, they are intersected by quarry operations, revealed during sinkhole collapses, or dug open by dedicated cavers.

Karst features serving as discharge points from the aquifer, i.e., springs, collectively release billions of gallons of water every day from the Floridan Aquifer System. Many of these springs are subjacent to the west-central coast. The west-central coast of Florida is on a broad continental margin with low slope; therefore, it is plausible, even likely, that the locations of these springs are transient and may change in conjunction with sea-level changes. It is also possible that during sea-level lowstands, many of these springs may have served as recharge points to the aquifer. A few springs in Florida, such as Madison Blue and Fanning Springs within the Suwannee River basin, behave as estevelles, recharging the aquifer during high river stages.

Karst features conducting water from input to output in the aquifer are less common and are associated with river systems; however, springs emerging from these systems are among the largest in Florida. Clear examples of river-type systems occur where surface streams sink and reappear some distance downstream. River-type systems are more numerous in north Florida and include the Santa Fe Sinks and Rise, the Steinhatchee River Rise, the Alapaha Rive Rise, Nutall Rise, and the St. Marks River Rise. The Curiosity Creek-Sulphur Springs System in Tampa is the southernmost example of a river-type system. The Woodville Karst System including Wakulla Springs, Leon Sinks, and the Spring Creek Springs Complex near Tallahassee is the best understood and likely the most extensive river-type system in Florida.

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