Friends of Nachusa Grasslands
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Geology of Nachusa Grasslands, Part 1

Karst Terrane: What It Is, Why It Is Here, and Why It Is Important to Nachusa Grasslands
Part 1:
What It Is

Karst is a German word that was derived from their name for a limestone plateau around the Adriatic city of Trieste.

Terrane is defined as a series of rock formations with a prevalent type of rock,

Today, karst terrane refers to land forms where porous carbonate rock formations, at or near the surface, are characterized by sinkholes, seeps, natural springs, or artesian wells.
Picture
Karst Rocks
Approximately 18% of the contiguous United States and only 10% of Illinois is defined as having karst or pseudokarst terrane. There are five regions in the state that are defined as karst, and all but the North-Central region are areas that were not covered by ancient glaciers. Nachusa Grasslands is located on the southeast edge of the North-Central karst region.
Karst is formed when layers of soluble carbonate bedrock, such as limestone or dolomite, are intermixed with layers of insoluble bedrock, such as sandstone or shale, which are then exposed to water.

As the water dissolves the carbonate rock, it forms vertical crevices and horizontal fractures. When these cracks become interconnected, the flow of the water forms the karst features.
Underground streams will form if the flow is relatively unimpeded by insoluble rock. And, if the soluble rock layer is thick enough, large cavities can be carved out which form caves when they are open at the surface. When a thinner karst feature is exposed, as in a road cut or bluff, seeps can form. Or, the water may exit as a spring or artesian well if the rock formations are underground and the water flow is impeded by insoluble rock, such as along a fault line.
Picture
Sinkhole Formation
Sinkholes occur when bedrock becomes so eroded it can no longer support the unconsolidated overburden (ground) above it, or the water level in a large cavity is lowered, leaving the ground above unsupported. Although sinkholes are usually formed by a sudden collapse of the ground surface, they are generally the end result of a long slow process.
Often precipitated by heavy rains saturating and softening the ground, sinkholes can also be caused by earthquakes and the sudden lowering of the water table.  These karst features also form large aquifers, which can be easily tapped for human use, and just as easily polluted.

Geology of Nachusa Grasslands, Part 2
Geology of Nachusa Grasslands, Part 3

All images from the University of Illinois IDEALS Repository

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  • Home
  • About Friends
    • Mission, Leadership, Objectives, and Financials
    • Endowments
    • Heritage Heroes Initiative
    • Friends Annual Reports
    • Newsletters >
      • PrairiE–Update (email)
      • A Prairie Calling (print and digital)
    • Friends Annual Meeting 2022
    • Commenting Policy
  • Plan Your Visit
    • Hours & Parking
    • Directions and Map
    • Visitor Center
    • Pet Policy
    • Public Bison Tours
    • Bison Viewing
    • Hiking >
      • Hiking Guidelines
      • Hiking Destinations
      • Stone Barn Savanna Tour
      • Visitor Center Trail
      • Scavenger Hunt
    • What's In Bloom?
    • Autumn on the Prairie
    • Exploring Nachusa Grasslands on Your Own
    • Things to Do
    • Places to Eat and Stay
    • Local Sites to Visit and Explore
  • Donate
  • Calendar
  • Volunteer
    • Volunteer Opportunities
    • Thursday and Saturday Workdays >
      • Workday Signup
      • Volunteer Workday Safety Protocols
      • Workdays – November to February
      • Leader Workday Safety Protocols
      • Steward Workday Tips
    • Stewardship Teams
    • Workday Email List
    • Steward Login
  • Stewardship
    • Nachusa Stewardship
    • Restorations
    • Planting Histories >
      • Stewardship Unit Planting Histories
      • Planting Histories in Chronological Order
      • Science Symposium Abstracts 2016
    • Stewards and Staff
    • Groups and Committees
    • Available Units
    • Controlled Burns
    • Prescribed Fire Recruitment
    • Restoration Publications
    • Stewardship Resources >
      • Weekly Top Picks
      • Seed Collection Guides
      • Invasive Plant Management
      • Invasive Identification
      • Monitoring
      • Links & Resources
  • Science
    • Science at Nachusa Grasslands
    • Science Grants >
      • Science Grants 2023
      • Science Grants 2022
      • Science Grants 2021
      • Science Grants 2020
      • Science Grants 2019
      • Science Grants 2018
      • Science Grants 2017
      • Science Grants 2016
      • Science Grants 2015
      • Science Grants 2014
      • Science Grants 2013/2012/2011
    • Science Symposium 2023
    • Science Symposium Abstracts >
      • Science Symposium Abstracts 2019
      • Science Symposium Abstracts 2018
      • Science Symposium Abstracts 2017
    • Potential Research Topics
    • Scientific Publications
    • Testimonials >
      • Dr. Holly Jones
      • Dr. Nick Barber
      • Kimberly Elsenbroek
    • Science Videos
    • Become a Community Scientist >
      • About Community Scientists
      • Butterfly Monitoring
      • Calling Frog Monitoring
      • Dragonflies & Damselflies
      • RiverWatch
  • About Nachusa
    • General Info
    • Prairie Smoke Annual Reports
    • Plant Inventory >
      • Common Names
      • Genus Species
    • Animal Inventory >
      • Amphibians
      • Birds
      • Bison Bison >
        • Bison
        • Bison Babies Broadcast Videos
      • Fish
      • Insects
      • Mammals
      • Other Arthropods
      • Reptiles
    • History
    • Jobs
    • Hunting
    • Geology >
      • Geology Part 1
      • Geology Part 2
      • Geology Part 3
    • 30th Anniversary Memories
    • Websites of Interest
  • BLOG AND MEDIA
    • Nachusa Blog
    • In The News
    • Photo Gallery >
      • Spring Photos
      • Summer Photos
      • Autumn Photos
      • Winter Photos
      • Visitor Photos
    • Submit Your Photos
    • Videos
  • Contact Us / FAQs