Mammoth Cave has a way of drawing people in.
A cold wind rises from the cave entrance and envelops the uninitiated.
“The first time I entered the cave, what struck me was that immediate visceral blast of cold air. You know a change is about to occur,” Davis McCombs says.
McCombs first descended into the earth at Mammoth Cave at the age of seven, on a tour with a grade school class. He came home obsessed. After 9 years as a seasonal ranger at Mammoth Cave National Park in central Kentucky, giving tours is no longer enough for McCombs. Now he writes poetry about this designated World Heritage Site which makes up the world’s longest underground network of natural tunnels
McCombs’ first book, Ultima Thule, is named after the rocks that were thought to mark the end of the cave system until 1908, when explorers found a small crawlway beneath and the rest of the cave beyond. His work won the 1999 Yale Younger Poets Contest and was recently published by Yale University Press.
It is the intricate labyrinth of tunnels, the mystical geologic and historic forces that shape them, and their fragile, dark loving inhabitants that inspire his writing.
A River Below the Surface The Green River carved this underground world out of limestone over millions of years.
The rock itself began forming 350 million years ago, something McCombs explains daily when he gives tours. “But as much we talk about it, we can’t really understand that. It is so much greater than our own life spans,” McCombs says.
To make a cave you need rock that will dissolve, and a way for water to flow through the rock, Joe Meiman, a park hydrologist, explains. Once water enters the rock, it wends its way through crevices in the soluble limestone, slowly enlarging tiny fractures into an underground riverbed. After at least 2 million years of water flow, the large caverns of the uppermost layer of the cave were formed, according to a new dating technique based on radioactive decay in quartz developed by Darryl Granger, a geology professor at Purdue University in Indiana.
Then the water table shifted downward, and began forming another level of the cave beneath the first. Mammoth Cave has four major levels, each descending deeper into the earth. Water runs through the rock beneath, where the cave is still forming.
McCombs writes of this etching process in The River and Under the River, “If I put my ear to the ground/ could I hear the drag of the river turning/ limestone into silt?”
A cap of more slowly eroding sandstone protects the upper levels of the cave from wearing away themselves, helping make this the largest recorded cave system in the world.
“Mammoth cave is immensity on the loose,” McCombs says. “My grandchildren will still be finding cave out here.” Over 350 miles of cave have been mapped so far, and some speculate the cave could have over 600 miles of corridors.
“No one has ever come/ this far — a dusty, Hell-bent crawl, past pits/ and keystones, to find myself deep in the ridge./ I was drawn to wonder, the margins of the map./ Breath and a heartbeat. A fading lamp./ I was coffled to the light,” writes McCombs in his poem Ultima Thule.
While hundreds of people wander this vast cave on tours, Meiman often works on his research in silence, just miles away in the same cave network.