We have discussed a little bit about volcanoes, and related the volcanic eruption to heat and pressure. To model that process, we can try the following activities:

a. Open a book on top of your desk. The pages represent layers of sediment (strata, pronounced "STRAY-ta") in the earth. Hold the center of the book with one hand while you push the edges of the pages (toward the center) with the other. The bulging in the middle is similar to the building of layers of sediment in the earth when pressure is applied.

Pockets formed beneath the layers sometimes fill with magma, creating more pressure on the layers. The pressure and the friction create heat.

b. Crumple a piece of paper, unfold it, and place it flat on your desk. When you push the ends of the paper toward each other, you will see that the pressure causes the
surface to wrinkle up along certain crease lines.

This suggests how mountains were formed along fault lines in the earth and that as they were formed, the extreme pressures may have changed the surrounding rocks.

c. Wrap 3 slices of white bread and 3 slices of brown bread in alternate layers in plastic wrap or waxed paper. (This makes 6 sedimentary layers.)

Place several very heavy books on the slices. After a day, unwrap the slices and note what changes have taken place.

You will realize that, in a similar way, sedimentary layers of rock are sometimes compacted by extreme pressures in the earth.