Mapping Karst

Mapping Karst

Workshop held at the NSTA convention in Nashville, TN December 3, 2005.
by Nancy Stetten and
Dr. G. Michael Clark, University of Tennessee at Knoxville.

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Nancy Stetten hosts a website on the geology of middle Tennessee www.nashvillefossils.com Material for her exercises are below

Maps are one of the richest and most fascinating sources of information about the world we live in. They not only convey facts but also reveal relationships among phenomena and so can be used to answer complex scientific questions.

Caves are among the most well know geologic features in Tennessee. Scientists are still struggling to understand exactly how they form, but one of the basic principles of cave formation can be seen by studying the map below.

This exercise compares the location of caves with the physiographic provinces of the state of Tennessee.

Examine the map below. (To print the map, use this link.) The red dots mark locations of major caves in the state. The color coding divides the state by the type of rock or sediment on the surface.

What is Karst?

Western Kentucky University has posted a useful introduction to karst. called The Karst Pages. The booklet defines karst this way. The word ”karst” refers to a type of terrain, usually formed on carbonate rock (limestone and dolomite) where groundwater has solutionally- enlarged openings to form a subsurface drainage system.

The Karst Water Institute has a useful list of karst resources for teachers.

Some typical features of karst are

caves
sinkholes
springs
seasonal or disappearing streams

Exercise 2: Sinkholes and Streams

This exercise compares topographic maps from two areas in Tennessee. A topographic map is one which gives information on elevation, showing lines of equal elevation every 20 feet. The US Geological Survey produces topographic maps which cover the entire United States. They also post a booklet on the Internet explaining topographic maps.

The two maps in this exercise cover the area around Cassville in Smith County and the area around Mansfield in Henry County. The map below shows the location of the two topographic maps. To print this map use this link.

Comparing karst and non-karst areas
Using the physiographic map above, what can you tell about the geology of the two sites.

Once you have become familiar with topo maps, look closely at our two sample maps and identify the hills and enclosed valleys. (again print them by following the links.).

Remember that topographic maps identify hills as enclosed figures.
Enclosed valleys are represented as hatched enclosed figures.

If you are using a hard copy, color the hill tops in one color and the enclosed valleys in another. What are the differences between the two maps?

Identify all of the streams on the maps. How do the patterns compare?

Making a three dimensional model of the sinkhole plain
Topographic maps can be difficult to read at first. Examine the map below and answer the following questions:

What is the highest point on the map? How high is it?
What is the lowest point on the map? How low is it?
How accurate are your measures of the highest and lowest points?

Making a three dimension model of a topo map can help students feel more familiar with them.

To make the model, I created templates using the map's lines of equal elevation. Print these template and copy them onto card stock. (To make a simple model use one copy of each template. To make a model with greater elevation, use two copies of each.

The Topography of the Glades

The Limestone Cedar Glades are another characteristi feature of karst. The Glades are areas in which there is little or no soil. This produces a harsh local environment with large variations in temperature and available water. In these harsh conditions, very little can grow, and many of the species found there are found nowhere else. For more on the glades, follow this link.

While cedar glades are a characteristic of karst they are not found everywhere in karst. The map below shows where cedar glades have been preserved by the Tennessee Division of Environment and Conservation.

Cedar glades are found in the part of the Central Basin called the Inner Basin. A region located on Stones River limestone, a limestone which is unusually pure. For more on the factors which cause the formation of cedar glades follow this link.

However, while almost all glades are in the Inner Basin, not all of the Inner Basin is covered with glades. Take, for example, Couchville Glade (# 12 on the map above). The satelite photograph below shows the vegetation in the area. Light colored areas are treeless glades. Trees can be seen in the darker areas