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MAKING MODELS OF TECTONIC PLATES

This activity suggests we make models of the earth's sedimentary layers and tectonic plates.

Set several strips of colored clay (alternate the colors), one on top of the other, to represent sedimentary layers of earth. Cut through the layers with a knife. The line or
crack between the two parts of the clay is called a fault line.

When we cut through the layers, we actually made models of two tectonic plates, and the cut is a model of a fault.

Now set the two parts side by side, and press them together by slowly increasing the pressure. Observe the folding, breaking, and shifting of the layers in each part. You will realize that mountains and valleys might be created in a similar fashion by shifting blocks of earth.

If you take them apart again and flatten them, you can see how earthquakes sometimes happen. Hold one block of the layered clay with one hand, and with the other hand, put the second block of clay next to it so that they touch. Holding the first block in place, move the second block forward (away from your body), and at the same time, press the second block into the first block.

You will notice that one block or the other (or maybe both, depending on how you are holding them) will start to bend. The earth, similarly, will "give" only a little, then, as
your model does (if you do it right!), the earth's plates will "unstick" and snap apart. That is what sometimes makes the earth shake, and you can see, by making the land unstable, it would cause buildings to break and to fall.

Some of the earth's plates come together in such a way that one rides up, over the other. The lower plate goes lower and lower until it melts, becomes magma, and erupts through a fissure (usually on a mountain). You can see that this type of plate movement can bring continents closer together, maybe by a few inches each year.

The earth's plates move slowly. When it reaches the point of ultimate stress, the result is quick and often catastrophic. Nature lets us know what is in charge!

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