Physical Geology lecture - Karst terrains

Lecture index:


Introduction

Karst: a landscape where soluble bedrock develops a distinctive suite of features.

Various soluble rock types that create karst features:

Photo to right is of a sinkhole collapse developed in gypsum (the whitish rock scattered about here). The image is from the French Alps.

Karst features:

The images below instruct as to the character of some of these features.

Small cave room in Fitton Cave. Note the abundance of speleothems, calcium carbonate forms that grow layer by layer and take a great variety of forms. Where they are wet they may still be actively forming as calcium carbonate mineral matter precipitates out of the water on to the outside of the form. The small hanging forms are known as soda straws. Note how some stalagmites and stalactites have recently connected to form the beginning of a column.

Note how the stalactites are concentrated along a line. This was a fracture along which the water traveled. When it hit the open cave air the chemistry changed so that calcite precipitation occurred instead of solution and the speleothems developed. The cave roof is flat because this much less soluble rock.

A particularly tall and thin column in a large chamber in Fitton cave. Layers within these types of formations are a bit like tree rings and carry a record of past water chemistry and temperatures.

Fitton and a host of other caves are home to unique species adapted for life in the cave. Since coloration is not useful in their dark world they often are white or pink. Eyes are often not well or fully developed. They live off of what washes in. Here is a pink salamander in a pool on the clay mud floor.

The motely caving crew, 4 of which were UNO students. Note the mud. Caving can be dangerous - make sure you go with someone who is experienced.

Valley floor near Fitton Cave. Note the grey, layered limestone cliffs, the cave opening to the right, and how portions of the channel are dry. All of these are typical of karst terrains.

Sinkhole lakes in Florida. Photo source from http://water.usgs.gov/ogw/karst/aquifers/floridan/features

Small sink hole feature in Florida. Note the limestone layers, and the USGS monitoring station. The level of water reflects the height of the groundwater table in this area. Image from: http://rnp782.er.usgs.gov/atlas2/articles/geology/a_karst.html

Image of researchers repelling into a sinkhole shaft in Missouri. From USGS site: http://pubs.usgs.gov/sir/2008/5023/09tennyson.htm

Diagram of karst features from USGS site http://rnp782.er.usgs.gov/atlas2/articles/geology/a_karst.html

Where is there extensive karst development in the U.S.:


Water chemistry and limestone dissolution

 

pH, which is the measure of acidity, plays a major role. For a refresher on pH - https://simple.wikipedia.org/wiki/PH .

The critical mineral is calcite - CaCO3.

Carbon dioxide plays an important role.

Calcite has reverse solubility wrt temperature.

Tufa deposits and the importance of organic activity (biologically added precipitation).

From USGS site: http://rnp782.er.usgs.gov/atlas2/articles/geology/a_karst.html

 


Formation of karst features

Phreatic vs. vadose and the role of the groundwater table:

Caves are geologically ephemeral and eventually fill in with:

Speleothems:

What causes solution and caves to form where they do:

USGS cross section of cave system from http://egsc.usgs.gov/isb/pubs/teachers-packets/exploringcaves/chapter2.html


Caves as treasure troves of information

This is a mammoth skull left within the fine-grained lake sediments that slowly filled up a sinkhole near Hot Springs, South Dakota. Each layer is a year. Other skeletons have been removed for study, but some were left so that people could see them in place.

As archeologic and paleontologic sites.

As record keepers of climate change.

Spelunking and safety issues.

Link to Mammoth Cave material: http://pubs.usgs.gov/sir/2008/5023/44toomey.htm

National Cave and Karst Research Institute - http://www.nckri.org/ - a good place for more information.

On to material about deserts.


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