Earth Cache
To Learn Something About Our Planet
The Lesson That You Learn Is Learned Forever
Leave Nothing But Your Footprints Behind
Hunting is allowed in this area. Wear orange during hunting season.
Karst Topography
Karst refers to geologic, hydrologic, and landscape features associated with the dissolution of soluble rocks, such as carbonates and evaporites. A common feature of karst landscapes are sinkholes which we will learn more about.
Sinkholes are formed when the land surface collapses into subsurface voids formed in the slowly disolving rock. In Iowa, carbonate rocks form the uppermost bedrock over roughly the eastern half of the state, and are mantled with a variable thickness of glacial and other unconsolidated materials. Where these unconsolidated materials are less than 50 feet, and particularly less than 25 feet thick, sinkholes may occur. There are three areas in Iowa where large numbers of sinkholes exist. The first is within the outcrop belt of the Ordovician Galena Group carbonates in Allamakee, Clayton, and Winneshiek Counties. Most of Iowa's sinkholes occur in this region. The second region in Bremer, Butler, Chickasaw, and particularly Floyd and Mitchell counties contain Devonian carbonates. The third region is along the erosional edge of Silurian carbonates in Dubuque and Clayton counties.
Carbonate rocks are the basis of sinkholes, caves, sinking streams and subsurface drainage. Dolostone and limestone are the most common carbonate rocks. Dolostone is the mineral dolomite plus some calcite. Limestone is calcite plus some dolomite.
Karst landscapes occur because mildly acidic waters slowly act upon soluble rocks. Water percolates through soil to the bedrock, where it interacts with fractures in the rock. Hundreds and thousands of years of pressure and chemical erosion from the water causes these fractures to grow. When the cracks become large enough that they cannot support the weight of the soil on top of them, a sinkhole forms. Sinkholes are natural depressions or holes in the Earth's surface. The result is an underground drainage system.
Most of the sinkholes found in Iowa are in Allamakee and Clayton counties, however due to the Karst landscape in this region of Mitchell County they are found here as well. The above map shows areas of sinkholes indicated by the orange circles that are in this section of Mitchell County. Most of the sinkholes that are found in Mitchell County are along either side of the Cedar River.
Let's now explore the two sinkholes of this EarthCache. You can park along the side of the road near the two sinkholes or continue down the road to a parking area and walk back. If you park along the side of the road be sure to pull over far enough so you do not block the road.
In order to log this Earth Cache several tasks need to be done.
First, take an elevation reading by your car. Next go to the listed coordinates of each of the sinkholes. At the East sinkhole coordinates mark your elevation and estimate how much deeper the low point of the sinkhole is. Do the same thing at the coordinates of the West sinkhole.
If you are able to determine the area of each sinkhole do this as well. If you are unable to determine the area, in your estimation which sinkhole is larger. After your observations message the owner the following.
1. Elevation reading taken next to your car.
2. Elevation at the East Sinkhole coordinates (include estimate of how much lower the low point is).
3. Elevation at the West Sinkhole coordinates (include estimate of how much lower the low point is.
4. The size of each of the sinkholes (either calculated or estimated)
5. Which sinkhole is deeper?
6. Not required, but nice, a photo of you or your team at either of the sinkholes.
A Special Thank You To The Mitchell County Conservation Department For Allowing This Earthcache To Be Developed.