Volcanoes Micro Workshop

What is a volcano?

A volcano is an opening in the Earth’s surface (or vent) through which molten rock (also called melt and magma) from inside the Earth spews out onto the planet’s surface. The word “volcano” most frequently refers to a mountain formed by the build-up of melt outside a vent.


How do volcanoes erupt?

Volcanic eruptions are due to a build-up and release of pressure. A volcano has a magma chamber underneath it; this magma chamber forms when magma formed in the lower crust of the Earth rises nearer the planetary surface. As more magma enters the magma chamber, the pressure increases until the magma can no longer be contained. The magma is forced upward through a vent in the rock above the magma chamber and erupts from the vent in the Earth’s surface.


What comes out of a volcano during an eruption?

Once magma has erupted from the Earth’s surface, it is called lava. Lava can flow down the side of a volcano in what is called a lava flow. If lava spews from the volcano in small blobs, these blobs can cool quickly in the air and form igneous rocks called tephra or cinders. Larger blobs of lava that erupt from volcanoes are called volcanic bombs. Very small droplets of lava that erupt from a volcano cool almost instantly and are called volcanic ash. Volcanic ash can rush down the side of a volcano in a sort of ash avalanche called pyroclastic flow, or nuée ardente (which means “glowing cloud” in French and gives an idea of what a pyroclastic flow looks like). Volcanic eruptions also expel a lot of gasses.


Are there different kinds of volcanoes?

There are three main types of volcanoes that form on land:


Shield volcanoes are broad and dome-shaped. Shield volcanoes are formed by lava with a low-viscosity (fast moving lava).

Cinder cones are cone-shaped piles of tephra. Cinder cones typically have moderate slope that makes them look like piles of sand. They are usually symmetrical and have a deep crater at the summit.

Stratovolcanoes, also called composition volcanoes, are large and cone-shaped; they are the classic image of a volcano. Stratovolcanoes are formed by alternating layers of lava flows and tephra. They are often steeper near the summit.


What type of volcano are we modeling?

We are modeling a stratovolcano. Our volcano has a cardboard skeleton to give it its starting shape. On top of the cardboard skeleton is a layer of paper with Mod Podge sealing the seams. Each week, we mix some debris in with our simulated magma/lava that erupts from the volcano’s summit. As the volcano erupts, this debris is left to accumulate on the body of the volcano. We seal in this debris with another layer of paper with Mod Podge sealing the seams. We repeat this process every week, allowing our volcano to build up alternating layers of debris (representing tephra) and smooth paper (representing cooled lava flow). After our final eruption, if we were to saw our model in half, we would be able to see the alternating layers that define a stratovolcano.


How do we make our volcano erupt, and how is that different from a real volcanic eruption?

We make our volcano erupt using a modified recipe for elephant toothpaste:


Elephant Toothpaste (safety goggles are a good idea!)

  • ½ cup hydrogen peroxide liquid (6%-8% solution)
  • 1 tablespoon liquid dish soap
  • 1 tablespoon dry yeast
  • 3 tablespoons warm water
  • Debris (such as gravel, dirt, sand, etc.)


Pour the hydrogen peroxide into the bottle or beaker being used for the eruption. Add about 1 tablespoon of liquid dish soap to the bottle or beaker, then swish the solution to mix it.


In a separate small cup, combine the warm water and yeast; mix for about 30 seconds. Then pour the yeast/water mixture into the hydrogen peroxide/dish soap mixture.


Elephant toothpaste “erupts” because of a chemical reaction caused by the interaction of its ingredients. Real volcanoes erupt due to a buildup of pressure in the magma chamber in the Earth’s crust directly below the volcano.