Tuesday, January 26, 2010

Missouri Caves: The Backstory

Missouri has been called “the Cave State” for years, and for good reason. We have plenty of that neat-o karst topography of sinkholes, springs, and caves, where water seeps into the earth, penetrates the limestone rock layers, then follows along cracks and fissures. Because the water carries with it chemicals from organic sources (think of the leaf litter that water passes through), it becomes mildly acidic (think of it as weak tea), and over time, the water eats away at the rock as it flows through, seeking someplace lower, seeking the water table.

The first stage is basically an underground river. This river is called a spring when it exits the ground. Picture a spring at the foot of a hill, where its water feeds into a creek or river. Then, think of what will happen after an overall, regional uplift: Bluffs are created as streams cut downward through rock; as the Ozark region was raised, many spring openings were lifted so high they were no longer at the water table. And those opened up into air-filled caverns. The former mouth of the spring is now the entrance to a cave.

Of course, water still drips in from above, etching the rocks above it, and redepositing minerals where it drips—thus the stalactites and stalagmites and other beloved cave formations. These features actually represent the later stages of a cave, where rock is gradually refilling the cavity.

When you think of the process—the initial fissure, the water table, the widening channel of the spring, the uplift, the cavern, then the (re)formation of geological features within it, you begin to realize this is much, much older than, say, the Grand Canyon. You begin to wonder: Well, when precisely do you say a cave “began to form”?

This process began tens of millions of years ago. What’s more amazing still is that some of the oldest caves are still down there, gaping full of water, hundreds of feet below the mouths of the big Ozark springs where they discharge.

No comments: