Sinkholes are as much a part of the Florida landscape as palm trees and alligators. There also has been a rise in sinkhole claims in Florida, but insurance officials believe some of those claims are questionable. WHY ARE THERE SINKHOLES IN FLORIDA? When the dirt, clay or sand gets too heavy for the limestone roof, it can collapse and form a sinkhole. WHAT TRIGGERS SINKHOLES? Although sinkholes are formed naturally, they can be triggered by heavy rainfall, drought followed by heavy rainfall, tropical storms and human activity. WHERE ARE SINKHOLES MOST COMMON IN FLORIDA? Three counties in the Tampa region are known as "sinkhole alley." Two-thirds of the sinkhole damage claims reported to the state Office of Insurance Regulation from 2006 to 2010 came from Hernando, Hillsborough and Pasco counties. Sinkholes are less common in South Florida, home to the state's two most populous counties — Broward and Miami-Dade. HOW MANY SINKHOLES OCCUR IN FLORIDA? The state Office of Insurance Regulation says reported claims from sinkholes have risen in recent years. HOW MUCH DAMAGE DO SINKHOLES DO? The state Office of Insurance Regulation says sinkhole claims in Florida cost insurers $1.4 billion from 2006 to 2010.