Viscous Buckle Folding

Phillip Resor
,
Wesleyan University
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Summary

This activity introduces students to viscous flow and analog modeling of viscous buckle folding. Students perform a series of experiments to explore the relationship between layer thickness and fold wavelength.

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Context

Audience

undergraduate core course in structural geology

Skills and concepts that students must have mastered

Students should be familiar with fold description. They should be familiar with viscous flow and linear viscous materials.

How the activity is situated in the course

This activity is done as a lab in my course prior to a field trip where the students measure wavelengths and layer thicknesses of pegmatite veins folded under amphibolite-facies conditions.

Goals

Content/concepts goals for this activity

ductile deformation, viscous flow, buckle folding

Higher order thinking skills goals for this activity

Analog modeling, model evaluation

Other skills goals for this activity

Description of the activity/assignment

In order to better understand ductile deformation and the growth of folds students perform a series of experiments with readily available viscous analog materials. Students begin by exploring the concept of viscosity and viscous flow problems by using Stoke's Law to measure viscosity of corn syrup from the terminal velocity of a falling steel ball. The students then complete a second series of experiments folding a stiffer material (fruit leather) within a corn syrup matrix. By varying the thickness of the fruit leather layer they discover the linear relationship between layer thickness and dominant wavelength predicted by viscous fold theory.

Determining whether students have met the goals

Students submit a report that documents their experimental methods, results, and answers discussion questions. In my class this activity is tied directly to field observation of folds that likely formed by a similar mechanism.

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