Daily Dose of Happiness US # 22 - Missouri Karst and Sinkholes Earthcache
Approximately two-thirds of Missouri is underlain by carbonate bedrock dolomite/limestone. When located at or near the surface the bedrock is prone to disolve into groundwater, creating features such as sinkholes, caves, springs, and losing streams. This terrain is called “Karst”.
In Missouri, Karst terrane is divided into 6 primary regions based on the underlying bedrock formations and the way in which the Karst features developed.
Pleasant Valley Nature Preserve is in the Ozark Plateau, and more specifically in the Salem Plateau. A deeply and intricately dissected plateau, mostly Cambrian- and Ordovician-age cherty dolomite bedrock. The bedrock is sedimentary, carbonate, dolstone: fine crystalline, silty, cherty dolomite, and oolite chert with local sandstone beds. The area features rugged hills with steep slopes and high cliffs, sinkholes and a cave.
There are three major types of sinkholes generally recognized by geologists: collapse, subsidence, and solution.
Collapse sinkholes- form as water dissolves the underlying rock forming cavities or caves below the surface. As the cave expands the top may no longer be able to support the weight from above and the roof of the cave collapses, causing a depression in the surface.
Subsidence sinkholes- form as water erodes the underlying rock by infiltrating the fractures and expanding them as the slightly acidic water dissolves the dolomite/ limestone. As the crack expands, sand, soil, etc. are carried by the water and fills the crack, causing a depression in the surface above the eroded rock.
Solution sinkholes- form in a similar way as subsidence sinkholes except that there is only exposed rock and no overlying sediments. As water infiltrates fractures in the soluble rock, it begins widening the crack forming a collection site for groundwater.
Logging Requirments:
The posted coordinates take you to a sinkhole, marked with a sign, along the trail system in Pleasant Valley Nature Preserve.
Email or message me from my Geocaching profile the answers the following questions:
1. Based on what you see here and what you know about sinkholes after reading the cache page, in which Karst region is this area?
2. What is the type of bedrock here?
3. Based on the types of sinkholes listed in the description and from looking at the sinkhole, how do you think this sinkhole formed?
4. As you walk along the trails to and from this earthcache, what clues do you see that the soil layer may be thin in this area?
5. Post a picture of yourself or a personal item at the sinkhole.
This earthcache is only available during Park Hours hours: Dawn to Dusk. Check for park closures during Bow Hunting Sesson.
This EarthCache adheres to the principles and ethics of geocaching and Leave No Trace. Use established trails only. Damage to the site is unacceptable. Please be mindful of fragile ecosystems. Please enjoy the area by collecting memories — not samples.
Permission to place this Earthcache was given by: Jefferson County Parks and Recreation Administration
Resources:
Missouri Department of Natural Resourses
https://dnr.mo.gov/land-geology/hazards/sinkholes
https://share.mo.gov/nr/mgs/MGSData/Open%20File%20Reports/Geologic%20Natural%20Features%20Classification%20System%20for%20Missouri/OFR-2019-112-GS.pdf
United States Geological Survey USGS.gov
https://www.usgs.gov/special-topics/water-science-school/science/sinkholes#:~:text=Sinkholes%20are%20common%20where%20the,spaces%20and%20caverns%20develop%20underground.
https://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=MOOjc%3B0
Jefferson County Parks and Recreation
https://www.jeffcomo.org/582/Parks-and-Recreation
Missouri Department of Conservation
https://mdc.mo.gov/discover-nature/habitats/caves-karst/sinkholes-sinkhole-ponds
