Tension gashes with Jell-O
Skills and concepts that students must have mastered
How the activity is situated in the course
Content/concepts goals for this activity
Higher order thinking skills goals for this activity
Other skills goals for this activity
Description and Teaching Materials
The night before class, I prepare Jell-O that is approximately 2-3 cm thick. In class, students first hypothesize about what happens to rocks when they are compressed. After defining a hypothesis (or multiple hypotheses, depending on the course), students sketch a diagram of the experiment (including arrows!). Students then break into groups of 2-3 and deform the Jell-O. They sketch what they see and experiment with a variety of techniques for deforming the Jell-O. For example, what happens if I apply force at an angle to the edge of the Jell-O? Is this similar or dissimilar to the first experiment? What happens if I apply compression and then dextral shear?
Students commonly get the Jell-O to fold, and the Jell-O often records a trace of the fold axis (best for synclines), even when unfolded. This fosters discussion of the variety of ways that rocks can respond to compression.
I wrap-up the exercise by having students describe via annotated drawings what they hypothesized, what happened and what the effects were of composite deformation events.
Teaching Notes and Tips
On a midterm, I typically ask students to interpret a photo of a sinistrally sheared tension gash.