Karst of Indiana
Karst is a type of landscape where the dissolving of the bedrock has created sinkholes, sinking streams, caves, springs, and other characteristic features.
- Contain soluble rock types such as limestone, marble, and gypsum.
- Karst landscape forms when water interacts with and enters the subsurface
- through cracks, fractures, and holes that have been dissolved into the bedrock.
- After traveling underground this water is then discharged from springs
Limestone Dissolution
- water contains dissolved CO2 (from air or organic matter in soil)
- cold water dissolves more CO2 (ultimately the controlling factor)
- forms a weak carbonic acid
- pH’s in limestone terranes dissociate acid into H+ & HCO3-
- CaCO3 dissociates & the CO3- links with H+ to form HCO3-
- Summary Equation:
- CaCO3 + H2O + CO2 > Ca2+ + HCO3-
Karst Cycles
Pre-Karst Topography
- The underlying bedrock at the surface is dominantly insoluble and is mostly intact.
- e.g., sandstone or shale
- Some limited karst features may exist
- The landscape commonly is drained by an abundant network of surface streams.
Early-Stage Karst Topography
- The insoluble caprock has been breached, and limestone is partly exposed at the surface.
- Surface drainage is very commonly limited and sinking/disappearing streams serve to divert surface water into the soluble carbonates.
- Exposed limestone areas exhibit an extensive sinkhole plain with little continuous surface drainage.
Middle-Stage Karst Topography
- There is very little surface drainage as most of the region is underlain by carbonates with extensive karst topography
- (sinkhole plain, solution valleys, etc.).
- The only vestiges of the caprock are isolated hills called monadnocks.
Late-Stage Karst Topography
- The underlying bedrock typically is an insoluble rock type
- sandstone or shale.
- There are only isolated remnants of karst landforms
- surface drainage once again dominates the land surface.
Sinkholes/Dolines
A sinkhole is a depression or hole formed when the land surface sinks due to underground bedrock dissolution or cave collapse.
Uvala
- compound sinkhole created from more than 1 depression.
Map
- The red marker is pointing to multiple sinkholes creating a uvala.
Polje
- large, flat-bottomed basin with steep sides that develops in karst terrains
- many sinkholes, sinking streams, etc.
Map
- You can see the may sinkholes that are associated with a polje.
Karst Window/Fenster
- solutional depression whose floor shows a resurgent spring whose water abruptly disappears back into the subsurface.
Map
- The map shows what a karst looks like on a topographic map.
- The window in is in the Orleans area of Indiana.
Karst Valleys
Typically develop in fluviokarst settings where the valley inherits many of its characteristics from the former stream
Dry Valley
- stream captured by sinkholes & diverted underground.
Map
- The dotted and dashed blue line on the map is the dry valley that the river would usually flow through.
Blind Valley
- valley that ends abruptly where the stream or river disappears.
Map
- The area between the two blue lines is the blind valley.
- The river abruptly ends at the top line and reappears at the bottom line
Interrupted Stream Valleys
- stream or river disappears at swallow hole and reappears at resurgent spring.
- may only be a karst window
Map
- Blue Path - path of the river
- Red Marker - were river disappears
- Green Marker - were river reapers
Caves
- Caves (typically under resistant caprock)
- vadose (zone of aeration)
- forms shafts/canyons; moves vertically along fractures
- speleothems- cave decorations that have ppt’d
- phreatic (zone of saturation)
- forms tubes at or beneath water table; controlled by drops in base level and down cuts
- when water table drops dissolution features.
