WATER RESOURCES OF ORANGE COUNTY 13
increased in size to about 60 feet in diameter and to about 15 feet in depth. The hole was filled and no further development has been noted.
Another sinkhole formed in 1961 in Pine Hills, west of Orlando. A depression about 1-foot deep and 50 feet in diameter that formed on April 23 and 24 was marked only by a faint line in the sand except where the outer edge intersected two houses. The floor of one room, the carport, and the concrete driveway of one house were badly cracked. The corner of the other house dropped about 6 inches. The slow rate of settlement was probably caused by a gradual funneling of the overlying sand and clay into relatively small solution channels in the limestone. The channels eventually became filled and the subsidence ceased.
A sinkhole formed rather rapidly in Lake Sherwood on May 22, 1962. This spectacular sinkhole removed a section of the westbound lane of Highway 50 and about 3,000 cubic yards of fill were required to repair the damage. According to eye witnesses, the sinkhole formed over a period of about 2 hours.
Sinkholes are most likely to form in areas of active groundwater recharge because the dissolving action of the water is greatest when it first enters the limestone aquifer. As the slightly acid water moves through the aquifer, it gradually reacts with the limestone and is neutralized. The prevalence of sinkholes is usually a good indication that the area is, or was in the past, an area of active recharge.
Sinkholes can either improve or impede the recharge efficiency of an area. In some instances, sinkholes breach the semipervious layers that separate the surface sand from the aquifer and permit water to enter the aquifer more readily than before. In other instances, lakes that form in sinkholes become floored with relatively impermeable silt, clay and organic material which retards the downward movement of water.
Much remains to be learned about the solution of limestone by water. Caverns have been discovered several thousand feet below the surface, and evidence indicates that active solution is going on at these depths. Present and future research by the U. S. Geological Survey and other agencies should provide much useful information about this important subject and its relation to ground-water movement and availability.