Frank Iiargadon, age 11 of Waddy, Ky., for his question:
Do all sinkholes lead to caves?
A sinkhole is a natural pit in the ground with lower walls that may lead to caves or tunnels. Some are steep holes that drop down several hundred feet. Others are shallow hollows, often filled with placid pond or lake water. When sinkholes form where streams and groundwater are scarce, they tend to be dry holes and hollows. These arid pits are less likely to erode caves, but a fees of them do.
Sinkholes fascinate spelunkers (cave enthusiasts) because these open topped pits sometimes lead down to mysterious subterranean excavations. Usually these are small caves near the floor of the shaft. A few are tunnels that lead to major cave systems. The floors of many sinkholes are flooded, and their cave entrances, if any, may be submerged.
The best collection of sinkholes is right there in your home state„of Kentucky. The world's champ is near Mammoth Cave. Its floor has an area of five square miles. South of the famous Hammoth cave system, in a region called the Pennyroyal Plateau, the earth is pitted with holes. This geological wonder is called the Land of a Thousand Sinks.
Most sinkholes and caves are eroded by the reaction of acid groundwater on rocks such as limestone or dolomite. As a rule, the erosion occurred in recent geological times. But the story began in the distant past, when limestone was formed and other crustal events occurred to set the stage.
Kentucky's fabulous caves and sinkholes are carved into a massive layer of limestone, 1,200 feet thick. The deposit began some 270 million years ago, when this region was submerged by a wide seaway from the Gulf to 1iexico. ,Then at last the water receded, the exposed limestone was topped with new deposits of shales and sandstones.
Later, a crustal upheaval lifted a wide hump, with slopes to guide the drainage. Some of the surface shales and sandstones were washed away. Fallen rainwater dissolved limestone calciums and other chemicals. Where the natural runoff of streams, this acid groundwater percolated down through the limestone. Its chemical reaction created the stupendous system of Mammoth Caves.
Just south of the caves, on a lowland called Pennyroyal Plateau, cave making is limited because streams and groundwater are scanty. Here the rains leave puddles that erode pits in the limestone. This is what created the Land of a Thousand Sinks.
Sinkholes and caves form in fragile rocks, likely to collapse without notice. The porous rock between several small sinkholes may crumble and form a larger one. The worn roof of a cave may give way and create a deep, open topped sinkhole. The floor of a sinkhole may be just waiting for an excuse to drop through the ceiling of a cave below it. A wise spelunker always carries rescue equipment, just in case. And he refuses to explore any excavation unless he goes with at least one trusty ally.