|Earth Science:||Earthquakes, Types of Faults|
|Grade Range:||Elementary School, Middle School|
This demonstration does require some preparation, but it will be deliciously worth it in the end. Students will be lining up to see (and eat!) this demonstration.
- Three 8in Square Cakes
- Bread Knife
- Serving Supplies (plates, forks, etc.)
- Two Large Spatulas
Please read the Physical Demonstration section of the Demonstration Safety page before performing this demonstration.
Before performing this demonstration, ask for a list of food allergies, if any, from the show contact. Do not perform this demonstration if you are unable to provide alternative options for any students with food allergies.
Create the Cakes: Either bake three cakes according to the directions given with the recipes, or purchase three cakes. If purchasing them, try to purchase them without icing. Slice the first cake down the center, and then ice it to hide the cut. Slice the second and third cakes down the center at an angle, and then ice them to hide the cuts. Be sure to label each cake with colored icing, labeling the first as "Strike/Slip", the second as "Normal" and the third as "Thrust".
- Show students the "Stirke/Slip" cake, and ask for ideas on what kind of motion this will be. Put a spatula under each side of the cake, and slowly slide one side of the cake towards you as you push the other side away. What do the students see happening to the icing on the surface?
- Show the "Normal" cake, and ask for ideas on the type of motion this could be. Put both spatulas under one side of the cake, and slowly pull it away from the other side. What happens to the icing this time?
- Show the "Thrust" cake, and ask for ideas on the type of motion this could be. Put both spatulas under one side of the cake, and slowly lift it while sliding it towards the other side of the cake. What happens to the icing on the surface this time?
- Finish by serving a slice of cake to each student! Only cut small pieces for the students, and cut the slices perpendicular to the fault lines in the cakes. That way, you can still show the types of earthquakes to other students as you serve out the cakes.
Why This Works
The earth's crust is not one solid piece, but rather is broken up into several large chunks called Plates. The plates are constantly rubbing against one another, and these areas of contact are called Fault Lines. There are three types of fault lines, but each one of them can result in earthquakes if there is a sudden jump in movement. A Strike/Slip fault is when two plates are sliding by each other in opposite directions. We see this with the cake when we slide one half towards us, and the other away from us. When there is a lot of movement, the land breaks and fractures as it is twisted in both directions, as we can see with the icing on the cake. A Normal fault is when the plates are pulling away from each other. In this case, the land crumbles as the rockbed below moves on without it, creating large crevices and canyons. A Thrust fault is when the plates are pushing into each other, and one of them is sliding on top of the other. This creates fractured land and rock, and is how mountain ranges are formed. Both of these cases are evident with the cakes as they are demonstrated.
- If you are good at decorating cakes, then make sure they all look like slices of the earth! The Strike/Slip should look like flatland, the Normal should look like a shoreline, and the Thrust should look like a mountain range.
- This demonstration pairs well with the Fault-y Spaghetti demonstration.