Caldera Demonstration Model

Dina:    Hi. I’m Dr. Dina. I work with the U.S. Geological Survey in Menlo Park, California with the Volcano Hazards Program. Today, we’re going to talk about calderas.

When most people think about volcanoes, they think of a triangle shape and that’s what many volcanoes look like, but there are other shapes too, and one of those is called a caldera. What we’ve done is created a simple experiment to show how calderas form. The experiment uses flour, a piece of tubing with a balloon attached to the end and a bicycle pump. So what I want you to imagine is that this is the surface of the earth in an area that’s volcanically active.

Underneath the surface of the earth, we’re going to inject some magma. When we inject the magma using our handy bicycle pump, it’s going to push the surface up, so let’s watch.

As you can see, the flower is being moved out of the way as we inflate the balloon or add magma to the system. The Volcano Hazards Program has monitoring equipment at different volcanoes to watch ground deformation such as this. In this case, what we’re going to do is we’re going to pretend that this large amount of magma erupts, sort of like when Yellowstone erupted or Long Valley Caldera erupted.

To do that, I’m going to let the air out of the balloon and then we’re going to watch to see what happens.

So as the air comes out of the balloon, we want to imagine the magma escaping from the magma chamber. Once the magma leaves the magma chamber, there’s nothing to hold up the overlying rock and so all that rock collapses down to where the chamber used to be. So you can see in our experiment the flour has now collapsed in a somewhat circular shape. We call this shape a caldera.

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