Watching the video:
Trying an experiment:
- What analogy is used in this sequence of the video to describe how
the earth behaves?
Figure 2 illustrates what happens.
- What happens when you push downwards?
- Can you see where the displaced water goes? Look again and this
time watch the air pocket as you try pushing on the rolling pin again.
It will help you see how the material under the load is pushed away and
where it goes.
- What happens when you slowly remove the load?
Figure 1: Here is the ziplock freezer bag half full of water and lying in the sink. This
is the form of the bag when there is no weight or load being placed on the bag.
This is the original form and the form to which the bag returns after the load
Figure 1 - Before and after the load
Figure 2: Here you see how the load deforms the bag and how the water is pushed aside.
Note the bulging affect of the displaced water. Can you see this in the real
Even though we know that the earth's crust is not plastic and the mantle
beneath the crust is not water, this demonstration can help us understand how
the earth behaves.
When a load is placed on it, the earth's mantle behaves partly like a viscous
material such as water. The upper mantle remains solid rock, but over a long
period (geologically) it can be thought of as flowing like very thick
molasses. And remember - the earth's components move very slowly, so slowly
that we do not notice the movement.
Figure 2 - During the load
Expected Answers from the students.