Folds and Faults
To learn why and how rock layers are folded and faulted and to learn how to represent the structures in maps and cross sections.
Tectonics is a general term referring to the large-scale deformation (or change) of rock in response to forces causing faulting and folding. The forces acting upon a rock mass are generally termed tensional (pulling apart), compressinal (squeezing together), or shear (parallel sliding). The magnitude and direction of the force (stress), the temperature and condining pressure on the rock, the composition of the rock, and the rate at which the rock is deformed determine how the rock changes in length, shape or volume. Common landforms resulting from tectonic processes are mountain ranges, rift zones, ridges, faults, fractured rock, and folded rock masses.
Tectonic features have been observed on all the terrestrial planets, the Moon, and the icy satellites of the outer planets.
The focus of this activity is on the folding and faulting of layered playdough which is used to represent layered rock. Folds show up best in layered rock but can also occur in unlayered rock such as granite.
Students begin by layering four colors of playdough to represent a horizontally layered rock mass with the oldest layer on the bottom. By pushing on the playdough block from two opposite side, the students apply a compressive stress resulting in the folding of the layers into an anticline. An anticline is a fold in rock that resembles an arch.
Preparation / Recipes
This activity calls for four colors of playdough to represent four different rock layers.
Play Dough (stove-top recipe)
-best texture and lasts for months when refrigerated in an air tight container.
2 cups flour
1/3 cup oil, scant
1 cup salt
2 cups cold water
4 teaspoons cream of tarter
food colorings (20 drops more or less)
Make this large batch one color or divide ingredients in half to make 2 colors. You will need 4 colors total. Combine ingredients and cook mixture in a large sauce pan, stirring constantly, until the dough forms a ball. Turn dough out onto a floured surface to cool. Then kneed until smooth and elastic. Cool completely; refrigerate in air tight containers.
Play Dough (no-cooking recipe)
2 cups flour
2 Tablespoons oil
1 cup salt
1 cup cold water
6 teaspoons alum or cream of tartar
food colorings (as above)
Make this large batch one color or divide ingredients in half to make 2 colors. You will need 4 colors total. Mix ingredients and kneed until smooth and elastic. Store in air tight containers.
After students have created an anticline in the layered playdough they will shave off the top, draw a map of the surface, and infer the interior structure. The fold is convex upward so the oldest rocks are in the middle. Next, the students will make a vertical cut through the playdough to represent a fault. They will slide the two halves of the playdough block horizontally in opposite directions to model strike-slip movement along the fault. Once the palydough has been offset along the fault another map of the surface is made. Finally, students look at one of the cut faces to draw a cross-sectional diagram of the structures and layers.
Have students compare their playdough structures, maps, and cross sections with their classmates' work.