Asked recently to list some of the biggest factors behind rising insurance costs, Florida Insurance Commissioner Kevin McCarty named the usual suspects, including the rising price of reinsurance and the overall economic downturn. However, he also mentioned something that most residents rarely ever see or think about: Sinkholes.

In a report to the Florida Cabinet, McCarty said that in some respects sinkhole claims present an even greater problem for insurers than other claims, including hurricanes where the cause of the damage is readily apparent. The problem is not just the sinkhole claims, but also the cost on insurers to investigate homeowners' claims for possible sinkhole-related damage. Testing for sinkholes and repairing damage, even in non-catastrophic cases, can cost well over $100,000. McCarty noted that insurers' complaints over sinkhole claims are not over legitimate claims, but rather the price of investigating an increasing number of complaints that may have more to do with normal ground settlement than with sinkholes.

Sinkholes are geological depressions caused when water erodes underground caverns and the land above shifts or collapses damaging homes and other buildings. While sinkholes can happen anywhere, two Florida counties make up more than 80 percent of claims — Pasco and Hernando, both north of Tampa. Those two counties harbor geological conditions that are most favorable for the development of a sinkhole. The land surface and the supporting sand and clay layers are thin, leaving the limestone base close to the surface. Due to the composition of the soil, if the water table drops or water erodes the limestone layer, a depression can quickly form, resulting in the total destruction of a home within days.