Monroe County has karst. What in the world is karst?

About twenty percent of the world has "soft" bedrock that is subject to dissolution, including Monroe County. Karst is an Eastern European term for sinkhole, which is what happens when soft bedrock dissolves and the topsoil subsides.

Although Monroe County has four water supply sources, Monroe, Frenchtown, Detroit and Toledo, about 14,000 households still rely upon wells and groundwater for their household source of water.

The Monroe-Lenawee Groundwater Stewardship Program has had a karst educational initiative for the past three years. In 2003 this effort focused in several areas; dye trace of Wittkop Drain last March, well water testing this past July, and a new karst poster shown at the fair and using GPS technology to identify sinkholes, artesian wells and springs.

Two exciting new developments include the initiation of a "karst area risk map" in cooperation with the Monroe County Planning Department and the construction of retention ponds along US 23, at Big Sink, in cooperation with the Monroe County Drain Commission and MDOT.

Because Monroe County has intensive and varied used of land, potential contaminants entering the groundwater could adversely affect a significant number of people and businesses. Where does this water go once it enters the ground? What can we do to identify, rank and "protect" water before it gets into a sinkhole? These are two questions that will be addressed over the next few years.

The Karst committee is looking for persons interested in volunteering to work on this project. Interested persons should contact Ned Birkey at the Monroe County Extension Service by email at: Birkey@msue.msu.edu or call 734 240-3170. Amy Gilhouse, Monroe Conservation District Groundwater Stewardship technician at amy.gillhouse@mi.nacdnet.net or 734 241-7755 Ext 3 is also available for assistance on karst and groundwater issues.

About Karst

Approximately 10% of the earth's surface (and 20% of the U.S.) is composted of karst; however, approximately 25% of the world's population lives on these areas! The hollow nature of karst terrain results in a very high pollution potential. Streams and surface runoff enter sinkholes and caves, and bypass natural filtration through soil and sediment. Groundwater can travel quite rapidly through these underground networks, up to thousands of feet, or even miles, per day transmitting contaminants to wells and springs in the vicinity.

In karst areas, the fractured limestone rock formations have been dissolved by flowing groundwater to form cavities, pipes, and conduits. Sinkholes, caves, sinking streams and springs signal the presence of underground drainage systems in karst-lands.

Conditions that promote karst development are well-jointed, dense limestone near the surface; a moderated to heavy rainfall; and good groundwater circulation. Limestone (calcium carbonate) dissolves relatively easily in slightly acidic water, which occurs widely in nature. Rainwater percolates along both horizontal and vertical cracks, dissolving the limestone and carrying it away in solution. Limestone pavements are produced by the removal of surface material, and the vertical fissures along joints are gradually widened and deepened, producing a grooved and jagged terrain. As it flows along cracks underground, the water continues to widen and deepen the cracks until they become cave systems or underground stream channels into which narrow vertical shafts may open. Most, but, not all of the principal cave areas of the world are areas of karsts.

How Karst was Formed

Between 570 million and 320 million years ago, the geographic area now occupied by the eastern United States was predominantly covered by a calm, hallow, tropical sea. The sea was populated by microscopic (and larger) organisms that lived, died, and sank to the bottom of lagoons, or were washed into deeper parts of the basin by storms. Over the eons, the deposits or calcium-rich shells and skeletons solidified into the bedrock that we call limestone, dolomite, and gypsum. These rocks are soluble in dilute acids. Water becomes slightly acidic when it takes up carbon dioxide while passing through decaying organic debris in the surface soils. The interaction of acidic water with soluble rocks such as limestone produces the characteristic landscape known as karst.

During the Appalachian Orogeny, a series of mountain -building events in the central and eastern U.S., rocks were alternately buried, uplifted, faulted, folded, and fractured. The geologic stresses of mountain-building and subsequent erosion created cracks and fissures in the rock through which rainwater and groundwater entered and actively dissolved the organic limestone. Within the past 10 million years, cave, conduits, and underground drainage systems have been dissolved into this rock by moving water. Surface water and streams are captured by underground channels. These channels convey the water to springs which sustain the water flow, cool temperatures, and aquatic habitats of our rivers.

Sinkhole Management

Sinkholes are natural drainage points for our groundwater system, so they should never be filled. If a sinkhole is plugged, water will not drain properly, may runoff onto adjacent property and possibly may cause flooding, subsidence, erosion, and pollution. The downstream springs, caves, wells, and streams which receive water from the sinkhole should be identified.

If collapsed sinkholes present a hazard to health and safety, and structures, they often can be stabilized in a way that maintains natural drainage abilities.

Always contact a geologist or engineer experienced in sinkhole repair before attempting to backfill or "seal" a sinkhole.

Do not locate a septic system, feed lot, animal waste lagoon, or storm-water basin near known or suspected sinkholes or caves. If sinkholes appear near such sources of bacterial contamination, use appropriate methods to prevent runoff from these areas from entering the sinkholes. Minimize unnatural or increased drainage into sinkholes.

Do not apply any fertilizer, pesticides, or other chemicals within at least 100 feet of a sinkhole. Notify your contractor of the location of all sinkholes.

Sinkholes are common throughout about one quarter of the U.S. Generally sinkholes can be recognized as circular or oval depressions in cultivated fields that my or may not pond standing water after rain events. Sinkholes can also have open bottoms, swallowing entire creeks, springs, or streams, which disappear underground. Both circumstances have one thing in common: caves and /or broken, weathered limestone bedrock near the soil surface. Over thousands of years, flowing groundwater gradually dissolved channels through the limestone. This process created underground caverns of various sizes which can not always support the weight of overlying soil and rock. A sinkhole is created when the surface materials collapse or are dissolved into the underground cavern or cave stream.

Surface water or irrigation runoff can wash soil sediment, fertilizer, animal waste, bacteria, and agricultural chemicals into the groundwater below. In sinkholes with open or rocky bottoms, this bypasses the natural filtration and biochemical breakdown processes that occur as water percolates through the soil.

Management Methods

If you have sinkholes or caves on your property, help prevent excessive runoff from entering groundwater by planting a vegetative barrier and/or fencing around the sinkhole.

Avoid structures that divert water naturally flowing into sinkholes. Soil-lined diversion ditches often collapse when storm-water erodes through to caves and underground cavities. The size and shape of the vegetated zone needed will depend on the slope of the land and the distance from the disturbed area. A 100 foot wide grass filter strip is ideal; a 50-foot strip is still helpful; and grass strips even as narrow as 13 feet can trap enough sediment to be effective. Filter strips will remove sediment only from shallow, sheet-type flows; they are less effective in deeper rapidly flowing water, such as in gullies or ravines.

Leave a wide natural buffer of trees and under story vegetation around sinkholes and caves when clearing land, harvesting timber, or disturbing ground in the drainage area.

Immediately after disturbing any soil, lightly fertilize, seed, and mulch the area to control erosion. A geotextile may be needed on very steep slopes. Water the area frequently until grass seed germinates. To protect embankments and channels until grass is established, build secure silt fences out of mesh plastic, anchored to the soil, and staked to hay bales.

Never dump trash, dead animals, or debris into sinkholes. This is illegal in most areas because it can directly and rapidly leach into springs and wells.

Some information taken from:
Encyclopedia Britannica
Living on Karst
The Karst Katalyst