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M. Seismic Hazards (Sinkholes and Subsidence) — Hazard <br /> Identification. Sinkholes are a common feature of Florida's <br /> landscape. They are only one of many kinds of karst <br /> landforms, which include caves, disappearing streams, <br /> springs, and underground drainage systems, all of which occur <br /> in Florida. Karst is a generic term that refers to the <br /> characteristic terrain produced by erosional processes <br /> associated with the chemical weathering and dissolution of <br /> limestone or dolomite, the two most common carbonate rocks <br /> in Florida. Dissolution of carbonate rocks begins when they <br /> are exposed to acidic water. Most rainwater is slightly acidic <br /> and usually becomes more acidic as it moves through <br /> decaying plant debris. Limestones in Florida are porous, <br /> allowing the acidic water to percolate through them, dissolving <br /> some limestone and carrying it away in solution. Over time, <br /> this persistent erosion process has created extensive <br /> underground voids and drainage systems in much of the <br /> carbonate rocks throughout the state. Collapse of overlying <br /> sediments into the underground cavities produces sinkholes <br /> (Florida Geological Survey, 1998). <br /> The Florida Center for Instructional Technology (2008) has <br /> recorded six sinkholes in Indian River County. The first three <br /> sinkholes developed in 1981; two were located in Fellsmere <br /> and the other in Vero Beach. All three sinkholes are less than <br /> 10 feet in width. The forth and largest developed in 1985, in <br /> Fellsmere and ranges from 31-80 feet in width. The fifth and <br /> sixth developed in 2002 and 2005, in Vero Beach and both are <br /> less than 10 feet in width. The Florida Center for Instructional <br /> Technology database does not document any sinkholes in <br /> Indian River Shores, Orchid, or Sebastian. (Maps, Etc., 2014) <br /> Vulnerability Assessment. There are areas in western <br /> Indian River County where canal bank failures could cause or <br /> exacerbate flooding during heavy rain events or storms. This <br /> problem is, however, more related to soil erosion than to actual <br /> levee failure. There has never been any seismic activity, soil <br /> failures, and few sinkholes in Indian River County. While these <br /> hazards may exist, County vulnerability to them at this time is <br /> considered very low. <br /> Seismic events can have the following potential impacts within <br /> a community: <br /> Indian River County Comprehensive Emergency Management Plan Basic Page 51 <br />