Nature Notes: Sinkholes and Springs in the Ozarks

by Jill Henderson – Show Me Oz –

Karst is crucial to the biodiversity of the Ozark region. At some point in its travel from heaven to sea, nearly three-quarters of the water in our rivers, streams, springs, aquifers, and wells have been filtered through this fractured limestone. This massive system of water movement and erosion is what makes karst one of the most bountiful and fragile geologic formations in the world. And while it’s beau Some of the water that falls or runs across our hills will become forever locked below the surface in aquifers, but a larger portion of it reemerges somewhere on the surface, usually in the form of a spring or a seep, or a wet weather stream.

The springs of the Ozarks are fed primarily by surface water collected by a large expanse of land called a watershed. Watersheds can be from several acres to several thousand acres and are collectively known as a recharge area. This recharge area funnels much of the surface water directly into streams and rivers, but a large portion of the water also finds it way into the underground system through cracks in the limestone and large, sometimes obscure voids known as sinkholes.

Sinkholes are essentially caves, or portions of caves that have collapsed. Some sinkholes are nothing more than potholes or small depressions in the earth, while others can encompass upwards of eighty acres or more. Sinkholes come in many shapes and sizes, but most take on the general shape of an inverted volcano. Ancient sinkholes are easily mistaken for small valleys, because their sloping sides have been worn smooth over time. Many are carpeted with grass, plants and large trees, making them tricky to identify.

Most sinkholes have an opening in or near their centers through which water drains into the karst system. While some of these openings are large and obvious, many are small and hidden beneath soil, rocks and vegetation. Some sinkholes completely fill with water during periods of heavy rainfall.

I once lived adjacent to several impressive sinkholes, one of which was one-quarter-mile across from rim to rim and approximately 50 feet deep at the center. It was a perfect inverted cone. The first time I came to the edge of it was in mid-summer when the vegetation was thick. It took a moment to comprehend what I was seeing because as I looked across it, I was literally looking straight at the very tip-top of a 50’ tall oak tree whose roots were firmly planted in the center of the sinkhole. I caught my breath. Wow. That’s a big hole.

I made it a priority to hike to the spot after the first real gully washer of the season to see what happened.

The downpour came that fall and washed over the Eleven Point bridge at Greer. I hiked to the rim of the sinkhole in the morning. I expected some water, but it was filled right to the very top. The leaves had fallen already and the trees stuck out of the water like match sticks. A pair of colorful wood ducks paddled around in the hole now filled with water. I wondered how long it would take to drain a sinkhole lake one-quarter of a mile in diameter and 50 feet deep. The answer was less than 24 hours!

I could almost hear the sucking sound as “Sinkhole Lake” swirled in a clockwise spiral, down and down, like the drain in my kitchen sink. Although I didn’t want to think about the possibly massive cave beneath my feet just at that moment, I’m pretty sure I know where all that water went. The Eleven Point river is a mere two miles away. Just above the river at Greer Landing, Greer Spring, dumps an average of 220 million gallons of ground water into the river, doubling its size. And a large percentage of the water emanating from Greer Spring started its journey from up here, on the surface.

That’s something we should all think about before changing the oil in our machinery, or spraying chemicals on the lawn, or even flushing the toilet – not to mention dumping garbage in a big earthen pit or –God, forbid – in a dry sinkhole (like some old-timers used to do before they knew better). Because every drop of the lovely, clear, cold water in our rivers, springs and seeps and the water in our aquifers and wells comes primarily from the surface.

Whether large or small, springs in Missouri and the sinkholes that feed them number in the hundreds of thousands. These geologic features are not only beautiful and necessary to the incredible biodiversity of the region, but hey shape the landscape, filter surface water, and generate micro-niches in which unique life forms thrive. but more importantly, they make us who we are as a people and a culture, and how we live and thrive in these hills we call home.

So the next time you look out over the beautiful undulating hills and deep hollows of the Ozarks, just remember there is so much more beneath the surface.

5 responses to “Nature Notes: Sinkholes and Springs in the Ozarks”

Jerre Miller | September 24, 2014 at 5:33 pm | Reply

We cannot have enough education regarding sink holes in MO & the karst typography. This is the best overview & description about sink holes I’ve read, Jill. Hope everyone who reads it can bring a new understanding of how groundwater can and does filter down into the limestone, caves and eventually our rivers & streams. Keeping this in mind is another reminder of how surface poisons can eventually work their way down into our wells and groundwater systems. Thanks, Jerre
- Jill Henderson | September 25, 2014 at 7:49 am | Reply
  
  Thank you, Jerre! A small part of the article came from the introduction to my book, A Journey of Seasons: A Year in the Ozark High Country. Sinkholes are a major contributor to ground water pollution and here in the Ozarks, particularly in the south central Ozarks, sinkholes are as common as oak trees. Unfortunately, many people don’t recognize them for what they are until it’s too late. I hope we can continue to raise awareness of sinkholes and the various roles they play in our environment.
Tom Kruzen | October 17, 2014 at 7:34 pm | Reply

Never put in a sinkhole what you wouldn’t want in your drinking water!
- Jill Henderson | October 18, 2014 at 9:01 am | Reply
  
  Exactly, Tom!
Pingback: Happy New Year & Thank You…for Everything! | Show Me Oz