Karst Landforms and Sinking Creeks

Every time I drive South Buffalo Road near my home, I pass by a completely dry creek bed. The width and depth of the creek bed is evidence that a fairly big creek once ran through here. The deep channel, cut by hundreds of thousands of gallons of water passing through each day, eroded the soil and exposed the rocks left behind.
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Along this same road I also noticed several large, circular depressions, which I learned are sinkholes. The sinkhole pictured below is only about 12 feet deep, but since I became aware that our area is filled with sinkholes, I have seen some much deeper. Sometimes their true depth is not known because the “bottom” is obscured by vines and tree limbs.

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This sinkhole, in  the middle of a grassy field, was formed a long time ago because the trees grew out of the hole once the area could no longer be mowed.

I did some research and found out that sink holes and “disappearing creeks” have a connection. The Ridge and Valley Province of the Blue Ridge where we live has a type of topography known as “karst.” Karst terrain is characterized by springs, caves, sinkholes, disappearing streams, and a unique hydrogeology that results in highly productive aquifers.

Karst terrain is largely supported by rocks such as limestone or dolomite that are highly porous and broken down by water. As water from streams or rainfall dissolves the bedrock, fractures occur. Over time, these fractures are enlarged and an underground drainage system begins to develop, allowing more and more water to pass through the system. Eventually, large hollow areas can be carved out underground and these unstable areas become vulnerable to earthquakes, construction, groundwater pumping, hurricanes, or other forces, which can cause cave-ins, or sink holes.

How a karst sinkhole is formed. Illustration by Denise Dahn (www.dahndesign.com/denises-blog/) for an interpretive sign at the Tongass National Forest in Alaska.

How a karst sinkhole is formed. Illustration by Denise Dahn (www.dahndesign.com/denises-blog/) for an interpretive sign at the Tongass National Forest in Alaska.

This sinkhole in Frederick, MD opened up in 2003. Many sinkholes occur along highways where rainwater runoff is concentrated into storm drains and ditches increasing the rate of sinkhole development (note the sewer drain pipe beneath roadway). Photo by U.S. Geological Survey.

This sinkhole in Frederick, MD opened up in 2003. Many sinkholes occur along highways where rainwater runoff is concentrated into storm drains and ditches increasing the rate of sinkhole development (note the sewer drain pipe beneath roadway). Photo by U.S. Geological Survey.

Streams that begin as runoff from mountain slopes often disappear into the subsurface when the water comes into contact with karst bedrock. These disappearing streams are called “sinking streams.” The water flows underground, emerging as a spring somewhere along the valley floor, sometimes miles away from where it plunged underground.

How water flows through karst bedrock. Illustration by Denise Dahn (www.dahndesign.com/denises-blog/).

How water flows through karst bedrock. Illustration by Denise Dahn (www.dahndesign.com/denises-blog/).

What all this means is that the creek I saw didn’t dry up – it’s what’s called a “sinking stream.” At some point along its course, the creek dropped through a fissure in the underlying rock and now flows underground. Because much of a karst watershed can be hidden underground, it’s hard to track exactly where water comes from and where it goes. I’m fascinated by the karst topography of the Blue Ridge, which means another post on this subject sometime in the future.

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20 thoughts on “Karst Landforms and Sinking Creeks

  1. We’ve got a little stream we walk across in the winter. Usually it flows all winter through the spring. This year the spring was so dry, it went underground right where we cross. You can hear the water flowing up stream, but then it just ‘pools’. Thanks to your illustrations and explanations I can imagine it coming out as a spring somewhere else.

    • We tend to think that water systems remain static, when, in fact, many things affect the water cycle and the hydrology of an area can change overnight.

  2. I find things like this very interesting and love to explore places where it happens. I found a stream last year that didn’t disappear under ground, but appeared from underground. I followed it upstream and suddenly there was only forest floor and no more stream.

    • Our neighbor has a spring that just appeared a couple of months ago for the first time. We had lots of rain this spring. Sometimes water comes off the mountain, traveling underground for a while, then percolates to the surface. Her spring may dry up this summer when the rainfall is down.

  3. I haven’t seen anything like this, but you make it sound very interesting. Look forward to hearing more on this subject.

    • Sink holes are scary because we don’t know what’s going on underground, but I can’t help but be intrigued. The acreage where I took this picture is for sale – there are four more sink holes on the property! I’d be scared to build a house on this lot.

  4. Nicely done explanation of karst – and thank you for including my illustrations! Ever since I’ve worked on those projects, I have been fascinated with the subject. Particularly love the limestone cave features like stalagmites They can be so beautiful!

    • Thanks, Denise. Your diagrams helped to explain how sink holes and other karst landforms are formed. They illustrate a process that occurs over a very long period of time that we cannot see.

  5. Thank you for a very well written explanation of karst landforms. Norther Michigan Has limestone for bedrock, and hundreds of sinkholes, some extremely deep. (over 100 feet)

    • I was surprised to learn that karst occurs in so many places. In my research I saw a terrifying picture of a huge sinkhole in Guatemala City that looked like it swallowed some houses. Terrifying stuff.

  6. The Ozarks are on a system of karst formations as well – the springs and creeks downward decent is stopped by a layer of shale here – the shale is the base of most live springs. A lot of early settlers thought they could get more volume from their springs by “opening them up” often with dynamite – this often damaged the shale layer and allowed the water to sink further causing the spring to dry up.

    • Water pumping in modern times can have the same effect of collapsing underground streams so that the water disappears further below the land surface.

  7. Thanks for the interesting post! I don’t know much about hydrogeology, but you do a wonderful job of explaining it. 🙂

    • I didn’t know that much about hydrology either until I researched sink holes. I had just assumed that once creeks were formed, they continued running unless they dried up from lack of rainfall, but learned there is much more to it than that.

    • We do live in a fascinating world and that’s just what I thought when I wrote about sinkholes and disappearing creeks.

  8. Pingback: The Creek Runs Through It | Adventures in Natural Beekeeping

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