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Look closely. Can you see that droplet of water?" The speaker was Randy Tufts. We were standing in his living room in Tucson in November, 1996. Kartchner Caverns had not yet opened as Arizona's 25th state park. We were talking about how the formations in the cave started from a single drop of water. Tufts stepped over to a photograph on the wall showing a cave wall in Kartchner Caverns. It looked like a textured drape with muted colors forming bands that dropped in a more or less diagonal pattern. Tufts pointed to a bright spot that seemed suspended in the blackness to the left of the wall. The image, he knew, was not merely a photo of a rock and some moisture, but a picture of a process at work. The tiny droplet in the photo had just fallen from the end of something called a soda straw, a narrow, glass-like tube of rock hanging from the cave's ceiling. The droplet of water seeped through the limestone, picking up calcium carbonate as it traveled; when the water hit the air in the cave, a chemical transformation occurred that eventually created the soda straw. The fragile soda straw, if it doesn't break under its own weight or get destroyed by someone colliding with it, will eventually grow into a stalactite, but that process will take thousands of years.

Typically, most stalactites and stalagmites grow only one-tenth of a millimeter per year, which is thinner than a strand of human hair. Having studied the buildup of these calcite deposits on primitive tools found in other caves, scientists estimate it would take more than 750 years to accumulate one inch. However, 750 years in the life of a rock or a cave is like the blink of an eye compared to the millions of years it takes to prepare for the creation of that single inch.

Before there can be a limestone cave, there must be limestone. Where did the limestone come from? How were the Whetstone Mountains formed? What forces were at work that created an underground cavern filled with so many exotic shapes and colors? The answers lie millions of years in the past. Some 200 million years ago, compacted limestone, formed 150 million years earlier from ancient marine life, was propelled upward by the buckling of the earth's crust and occasional volcanoes. These upheavals formed mountains in the inland sea that once covered what is now Arizona. Later, movements in the tectonic plates under the earth created great cracks and fissures that allowed water to penetrate the limestone deposits in places like the Whetstone Mountains, creating, about one million years ago, the cave now called Kartchner Caverns.

Compared to granite or shale, limestone is a highly soluble rock. As rain falls, it combines with the air¹s carbon dioxide to form a weak carbonic acid solution, which seeps through millions of cracks in the mountain's surface and dissolves the limestone. In the final stages of this cave's development, the level of the underground water dropped, leaving open chambers in the limestone. The first drop of water to seep through the mountain's surface soils and reach that ancient cavity began the process of decorating Kartchner Caverns with the stunning variety of calcite formations visible today. While the shapes and colors of the formations in Kartchner vary considerably, depending on minerals carried in the water and the trajectory of the water, the chemical process is the same. Acidic rainwater seeps underground and when it reaches an air-filled cave, it loses its carbon dioxide and crystallizes into calcium carbonate. If we could speed up this process enough to watch it happening, we would see that each droplet of water, carrying its load of dissolved minerals, hangs from the ceiling before it drops to the floor. Even in that brief time, some of the carbon dioxide escapes from the water, causing a ring of calcium carbonate to form on the ceiling. Later, another droplet hangs from this spot, and in the same way it adds a layer of mineral to the ring. directions carefully.

Text provided by Arizona State Parks

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