Controls on the Development of Rock Weathering Pits

Ellen Cowan
Appalachian State University
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Weathering pits are saucerlike depressions etched into rock by granular disintegration and spalling of thin rock flakes (chemical weathering processes). Their specific shape and size may be controlled by numerous factors. Visit a site with outstanding examples and develop multiple hypotheses for how and at what rate they form.

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Used in a field based laboratory in an undergraduate geomorphology course.

Skills and concepts that students must have mastered

Students work in groups of three. They make observations and measurements of the pits including orientation, and pit geometry. They plot their data and write up a paper outlining their favored hypothesis.

How the activity is situated in the course

This exercise takes two lab periods: one spent on general observations and another spent making measurements. Students work on their data and papers outside of class.


Content/concepts goals for this activity

Collecting field data (laying out a grid, making systematic measurements) and interpreting data.

Higher order thinking skills goals for this activity

Formulation of hypotheses based on initial observations, testing hypotheses with field data.

Other skills goals for this activity

Working together in a group. Keeping track of data collected in a field notebook. Paper writing based on original data.

Description of the activity/assignment

Weathering pits are well known from granite terrains and they also form in metaquartzite along the Blue Ridge Parkway in North Carolina. We will drive to Flat Rock Trail, along the Blue Ridge Parkway near Linville, NC. After a short hike up the trail we will observe the weathering pits exposed on the bedrock surface overlooking the Linville Valley. Each group of students will write down 3 hypotheses for how and why they form. Consider what factors control the size and shape of the pits. Collect data that can be used to test the hypotheses including orientation, size, and shape. Plot the data collected in the field. Present data on graphs and charts. Do trends in the data support one hypothesis over another?
Designed for a geomorphology course

Determining whether students have met the goals

Each small group of students prepare a laboratory report. The report should include all data collected and clearly describe the hypothesis that is best supported by the data.

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Other Materials

Supporting references/URLs

Another site that has many well developed weather pits is Stone Mountain in North Carolina. A reference for this is: Merschat, C.E., 1989, Stone Mountain, in Carpenter, P.A., III (ed.) A Geologic Guide to North Carolina's State Parks. North Carolina Geologic Survey Section, Bulletin 91. p. 59-60.