Present the cake as a rough approximation of a flat planet Earth.
From the background reading students should recognize the United States Geological Survey image of major plates. Bring this image up on the overhead projector.
Ask the students to describe the three types of plate movements; convergent, divergent, transform.
Slice off 1/3 of the cake along the long axis.
Take the 1/3 section with both hands at opposite ends (long way).
Begin to pull apart. Have the students pay attention to stress and strain on the internal layers. Ask the students if they know what the result will be. An example is sea floor spreading.
Flip the remaining 2/3 of cake over and cut through along the long axis 3/4 of the way. Flip back over.
Grab with one hand on each long side and begin sliding your hands in opposite directions. Pay attention to the damage done to the cake as you pull. Ask the students what kind of natural phenomena might occur with this motion.
Finish cutting into two pieces if the transform demonstration did not completely tear through the cake.
Cut one of the long strips you just made in half. When plates drift they will either run into each other and push up or the lighter (younger) plate will slide over the older (subduction).
Push the cut halves into each other to demonstrate the creation of a new mountain peak. Pay attention to the colored cake layers as the mountain is created. Ask the students to speculate about the layers of the rock of those mountains. How can geologists use this information to study the surface of the Earth?
Cut the last strip of cake in half. Demonstrate subversion by sliding one piece under the other as they collide. Volcanoes are very common with subversion. Mariana Trench is the lowest elevation point in the world and comes from converging oceanic plates.
Feed the cake to the students.