Sinkhole season: Why now?

By Michael Gannon March 27, 2014

Mike GannonSinkholes can happen any time, but for a number of reasons they’re more prevalent from early spring until late summer — the unofficial Florida “sinkhole season.”

The entire state of Florida is vulnerable to sinkholes. From the Florida Keys to Georgia, the state sits on a soluble limestone foundation, which dissolves fairly easily in water.

Sinkholes occur when water filters through the limestone, slowly eroding it. Rain exacerbates the erosion when it becomes acidic on its way through the ground and reacts with decaying vegetation. Eventually, the erosion forms large voids or cavities in the limestone. When the limestone ceiling can no longer support the weight of the soil above, the ceiling collapses, causing a sinkhole.

The Florida sinkhole season starts after the winter dry season. During winter, the groundwater dries up, and underground cavities created by the erosion dry out. The onset of spring brings several factors that can trigger sinkholes in the vulnerable limestone.

  • weather — Spring is the rainy season in Florida. Heavy rainwater puts pressure on the dried-out limestone surrounding the empty cavities. The water further erodes the limestone and increases the weight of the soil above. This combination weakens the support and increases the pressure on top of the caves, resulting in collapse.
  • agriculture — Farmers pump groundwater to spray their crops in a cold snap, covering them with ice to protect them from extreme cold. As a result, underground aquifer levels can drop by tens of yards overnight. Such quick changes in hydrostatic pressure destabilize soil and weaken limestone. The weight from the soaked ground can result in collapse.
  • development — Spring brings a new construction season. Construction can require the diversion of surface water, resulting in focused infiltration of surface runoff, flooding, and limestone erosion.

The conditions above exist every year. Some years bring additional triggers. For example, sinkhole reports increase in drought years. Unusually dry or wet seasons can even lead to short-term reversals in the direction of vertical water flow, further exacerbating sinkhole activity.

While sinkholes are more prevalent from spring through late summer, they can happen any time of year and anywhere in Florida.

Verisk’s Sinkhole Service can help you understand and manage your exposure to the risks associated with sinkholes.


Michael Gannon

Michael Gannon, director of Marketing for Verisk Insurance Solutions, is responsible for strategic marketing in support of Verisk underwriting auto and property solutions. Before joining Verisk, he held similar positions at Verisk’s Xactware and AIR Worldwide.