National Geographic : 2009 Jun
• 0mi 20 0km 20 TAG Cave Density Caves per square mile 3715 Featured cave TENNESSEE ALABAMA GEORGIA CUMBERLAND PLATEAU APPALACHIANMTS. Ellison's Devilstep Hollow Rumbling Falls Sub-Solomon Thunderhole Jaguar Iron Hoop Stephens Gap Nashville Huntsville Chattanooga Lookout Mt. Cookeville Sequatchie Tennessee A B CROSS SECTION BELOW beam we can barely make out the walls around us. e chamber is the size of a small but very high-ceilinged gymnasium. "Look up and right," directs Bobo. As we shine our headlamps onto a wet rock wall, a rope appears, dangling out of the upper black- ness. One by one we ascend the rope. At the apex of the domed cavern we traverse along a sloping ledge over the invisible seven-story drop we ve just climbed, then enter another tunnel. It s large enough that we can stand up and walk for more than a thousand feet before the passage is solidly plugged by a pile of boulders and dirt--- a breakdown, where the ceiling has collapsed. is is as far as any human has probed. Our team believes the passage continues on the other side of the breakdown, so our goal is to "push" the cave: Go beyond what is known into the invisible unknown. We divide into two par- ties, mappers and diggers. Smith and Bobo will survey the borehole; I volunteer to be a digger. When it s my turn, I lie down on my belly and shimmy to the end of a hole beneath the breakdown. Flat on my stomach, the ceiling pressing down on my neck, walls forcing in on the sides, I hold the shovel stretched out in front of me and furiously jab at the dirt wall. Chunks of earth fall all around me as I dig like a berserk badger. Several times I ll a drag tray, pushing it beneath me and then backward with frog kicks, where it is emptied by the other cavers. But soon the hole is too narrow, and I dispense with the 0mi 600 0km600 UNITED STATES AREA ENLARGED Atlanta B A Sea level 1,000 ft Limestone layers Non-cave-forming layers of limestone, shale, and mudstone Sandstone-and- shale cap Crow Mt. Tennessee, Alabama, and Georgia---cavers call the area TAG---boast 14,665 known caves. The highest density of caverns (left) is found on the Cumberland Plateau. Generous rainfall and numerous rivers and streams meet layers of porous limestone lying under a sandstone cap (cross section below), creating textbook condi- tions for cave formation. MARTIN GAMACHE, NG STAFF SOURCES: ALAN CRESSLER, NATIONAL SPELEOLOGICAL SOCIETY; ALABAMA CAVE SURVEY; GEOLOGICAL SURVEY OF ALABAMA; GEORGIA SPELEOLOGICAL SURVEY; TENNESSEE CAVE SURVEY; USGS Cross section shows relative position of limestone layers in which most TAG caves form.