Depending on where you live, you and/or your students may never have experienced an earthquake firsthand. However, each and every one of you surely know what an earthquake is, and what sorts of damage they can cause. The difficult thing about teaching about earthquakes is that, while the effects can be easy to see, the cause usually isn’t. So, just what causes earthquakes?
Earthquake Analogues with 1/3 of A S’more
This Demo Science science demo is as easy as it is delicious. All you’ll need is one (1) graham cracker per student. Any extras can be used for further experimentation and/or eating. My brain says do more experiments, my belly says eat ‘em all! It’s a win-win, really.
Have each student break his or her graham cracker in half along one of its perforations, the short way. If you somehow found store-bought graham crackers without perforations, you are clearly some sort of dark wizard and should be exiled from the village before you wittingly or unwittingly unleash the Evil sealed away within said crackers upon the world of man.
Next, have your students place their graham cracker halves back together so the edges where it broke apart are touching. With the kinda-sorta reassembled crackers laying on their desks, instruct them to move one piece toward themselves and one piece away, keeping the pieces touching all the while. They’ll surely note the small crumbs this process creates as the two halves scrape against each other.
Now, have each kid break one half of his/her halved graham cracker in half again, not using any perforations that may remain. The resulting pieces will, of course, have ragged edges. Then, have the students reassemble those pieces and repeat toward-and-away scraping step. These graham cracker pieces will not slide along each other’s edges as excellently, and will produce even larger crumbs.
Science. Delicious, Delicious Science
Sliding the graham cracker pieces past each other creates a model of a transform vault—that is, the area in the earth’s mantle where earthquakes occur. As tectonic plates, here represented by the cracker pieces, move, tension builds up, which causes vibrations that ultimately grow into earthquakes.
Where these faults are smoother, as with the first part of the experiment, the pressure is lighter. With more jagged faults, as in the second run, it’s much harder for the tectonic plates to move past each other. This results in a larger and more potent earthquake with larger debris, as the mass of crumbs now on your classroom floor can attest to.