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G <br />f <br />40 <br />In June 1893, Jacksonville experienced a <br />minor shock that lasted about 10 seconds. <br />Another earthquake occurred in October 1893, <br />which also did not cause any damage ( Zirbes, <br />1971). <br />In November 1948, doors and windows rattled <br />in Captiva Island, west of Ft. Myers. It was <br />reportedly accompanied by sounds like <br />distance heavy explosions (Zirbes, 1971). <br />In November 1952, a slight tremor was felt in <br />Quincy, a town located 20 miles northwest of <br />Tallahassee. Windows and doors rattled, but <br />no damage was reported (Zirbes, 1971). <br />3) Sinkholes and Subsidence <br />Sinkholes are a common feature of Florida's <br />landscape. They are Ione one of many kinds of karst <br />landforms, which include caves, disappearing <br />streams, springs, and underground drainage systems, <br />all of which occur in Florida. Karst is a generic term <br />which refers to the characteristic terrain produced by <br />erosional processes associated with the chemi.:al <br />weathering and dissolution of limestone or dolomite, <br />the two most common carbonate rocks in Florida. <br />Dissolution of carbonate rocks begins when they are <br />exposed to acidic water. Most rainwater is slightly <br />acidic and usually becomes more acidic as it moves <br />through decaying plant debris. Limestones in Florida <br />are porous, allowing the acidic water to percolate <br />through them, dissolving some limestone and <br />carrying it away in solution. Over time, this <br />persistent erosion process has created extensive <br />underground voids and drainage systems in much of <br />he carbonate rocks throughout the state. <br />Collapse <br />of overlying sediments into the underground cavities <br />produces sinkholes (Florida Geological Survey, <br />1998). <br />Indian River County Comprehensive Emergency Management Plan Basic Page 26