Tag Archives: Karst

05Mar 2012

Karst Features: ASBOG Sample Questions (Sinkholes, Polje, Uvala, Terra Rossa)

⋅ Leave a Comment

Karst may not be a common term to many of you who does not live in a limestone country. However, karst is common name given to the various landforms formed in a limestone region. For example, if you live in Florida, you probably know about sinkholes and caves. If you are from Hawaii, you may not!

The Great Blue Hole, located near Ambergris Caye, Belize.
The Great Blue Hole, located near Ambergris Caye, Belize.

KARST features are important for all geologists. Especially if you are studying for the ASBOG Geology examination for PG/FG certification, learning and identifying the Karst features is a must. I am including a test on KARST features along with the article which would test your knowledge. You can just take the test if you are comfortable with your Karst expertise.

Karst is defined as “a terrain with distinctive landforms and drainage arising from greater rock solubility in natural water that is found elsewhere.” (Jennings, 1985).Karst landform could form in any terrain underlain by limestone, dolomite, gypsum or other types of easily soluble rocks.

Did you know?

  • 40% of US population receive water supply from Karst aquifers
  • About 20% world landmass is Karst

Why is Karst Important to us?

  • Karst plays major role in controlling surface water.
  • Karsh aquifers are often prolific source of groundwater too.
  • Ground water in Karst terrain could be easily polluted due to highly fractured nature of the rocks and easy water infiltration through solution cavities.
  • Karst could be hazardous. Especially important for property damage.

What do you need to form Karst?

  • At least 60% calcium carbonate must be present to form Karst landform
  • 90% calcium carbonate rocks form “well developed” karst features.
  • Moderate to abundant rainfall
  • Interconnected fractures
  • Calcium Carbonate geochemistry is the controlling factor in Karst terrain. Calcite is the most important mineral. Although some other carbonates many also play some role in Karst landforms. Equation: CaCO3 + H2O + CO2 à Ca+2 + 2 HCO3-

Drainage pattern is highly unique in Karst Terrain

  • Holokarst – Precipitation moves directly underground; minor, if any, channelized flow.
  • Fluviokarst – karst landforms are superimposed on former fluvial landscape.

 

 

Recommended Text Books:

Karst Landforms

  • Terra – rossa or “red soil” (CL-CH): red clay-rich soil found at the upper surface in Karst terrain. Clay is left behind after the dissolution of limey material. If the soil is above the water table, oxygen promotes formation of rust (iron oxide) to give a red color to the soil. A great soil type for wine production.
  • Lapies – surface features characterized by fluted surfaces separated by deep grooves. Lapies form along joint surface with greater solubility.


Humid, Temperature Climates

  • Dolines (sinkholes): Dolines are small, shallow circular depression with funnel shape; they are commonly shallower in depth and width. Sinkholes are most common feature in Karst terrain.

–        Solution Sinkhole: related to subcutaneous zone, developed due to solution of rock underneath.

–        Collapse Sinkhole: material fails into subsurface due to cavity.

  • Uvala: large closed depression formed by coalescence of one or more sinkholes /dolines.
  • Karst Window: In general when the surface of a cavern breaks, it reveals the flow underneath from one cavern to another. Such feature is known as Karst Window.
  • Karst Plain: It is a geomorphic featured characterized by closed depressions and subterranean drainage in karst region.
  • Swallet (swallow hole):  Swallet is a place where water disappears (enters) underground in karst region.
  • Sinking Stream / Sinking Creek:  Any stream or creek that disappears underground, usually at terminus of blind valley.
  • Blind Valley: A Blind Valley is a valley that ends abruptly where stream vanishes underground. 
    • Resurgence: Resurgence is the point where waters from sinking stream re-emerge from underground.
    • Dry Valley: Dry valley refers to valley that no longer exhibits channelized flow.
    • Cave: A natural underground room or series of rooms large enough to be entered by a person.
    • Natural Tunnels and Bridges: Tunnels and bridges are formed by underground flow of water. When tunnel section collapse, it results the formation of bridges.
    • Hum: Hill-like features left behind after erosion in Karst terrain.
    • Polje: A polje is a large flat plain in Karst territory, with areas usually 5 to 400 km. Long axis of Polje develops in parallel with major structural trends and can become several miles (tens of kilometers) long


Humid, Tropical Climates

  • Cockpit Karst: a conglomeration of closed depressions surrounded by conical hills – similar to cone karst where depression is star-shaped.
  • Tower karst: Type of karst characterized by isolated, steep-walled hills separated by flat lying plain of alluvium.

Depositional Features

  • Travertine: Travertine is the calcium carbonate precipitate as coatings in cavern walls.
  • Dripstone: Dripstone is a type of Travertine forms due to the dripping of carbonate rich water from the ceiling if a cave/cavern – Stalactites forms at the roof, stalagmites form at the floor.
  • Helictite: When there is not enough water to form dripstones, an irregular deposit forms in the cave known as helictite. Helictites are a type of cave formation (Speleothems)

 Take the Test

ASBOG Sample Questions on KARST

Sample question on Karst. If you planning to take the ASBOG test, this may help.
Start

Congratulations - you have completed ASBOG Sample Questions on KARST.

You scored %%SCORE%% out of %%TOTAL%%.

Your performance has been rated as %%RATING%%


Your answers are highlighted below.
Return
Shaded items are complete.
12345
678910
End
Return

More resources for Karst Features: