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Volcano in the Classroom

Heather Haley
Product Developer

Background

The structure of the earth has 3 basic parts: the heat-producing core; the ductile mantle; and the thin, rigid crust. See Fig. 1. The mantle separates the outer crust of our planet from the core at its center.

The core is separated into 2 regions: inner and outer. The inner core is the hottest part of the earth. In spite of the intense heat generated there, the intense pressure exerted on the core keeps it solid. By comparison, the outer core, which is under less pressure, is liquid.

The mantle is also divided into regions. Above the outer core is a rigid layer of mantle called the mesosphere. On top of the mesosphere is the asthenosphere—a viscous layer of mantle that moves very slowly under pressure. The uppermost layer of the mantle is cool and contains rigid, brittle rock. This portion of the mantle is part of the outer shell of the earth, called the lithosphere.


Figure 1: Internal structure of Earth. Illustration courtesy of U.S. Geological Survey.

Figure 1   Internal structure of Earth.
Illustration courtesy of U.S. Geological Survey.


The lithosphere also contains the earth’s crust, which can be oceanic or continental. Although both are made of solid rock, continental crust is thicker and less dense than oceanic crust. When temperature and/or pressure increase, parts of the lithosphere can melt and create molten rock. When the molten rock forms underground, it is called magma. Magma can collect in a pocket under the crust called a magma chamber.

If conditions are right, temperature and/or pressure inside the magma chamber can increase and push magma into the crust above it. If the magma chamber is located near a weak place in the earth’s crust, the crust can break open and create a volcano. A volcano allows gases and molten rock, now called lava, to escape to the surface.


Materials


Teacher preparation

  1. Light the candle using a lighter or match.
  2. Tilt the beaker to one side.
  3. Drip melted candle wax into one side of the beaker, close to the bottom. See Fig. 2. You will need to accumulate about 2 tsp of wax. Note: When this demonstration is complete, the beaker may be cleaned and returned to regular laboratory use.


    Figure 2   Melted wax in beaker.

    Figure 2   Melted wax in beaker.


  4. Wait 5 min for the melted wax to cool and solidify.
  5. Add a 1" layer of sand over the wax in the beaker.
  6. Fill the beaker containing sand and wax with water until it is ¾ full.
  7. Dampen the sand by gently lifting and stirring it with a spoon. Note: Be careful not to dislodge the melted wax in the beaker.
  8. Wait 1 min for the sand to settle.



  9. Figure 3   Wax, sand, and water in beaker.

    Figure 3   Wax, sand, and water in beaker.


Demonstration procedure

  1. Slowly heat the beaker of wax, sand, and water on a hot plate using medium heat. See Fig. 3.
  2. As the wax melts, it will push up into the sand layer. See Fig. 4. During this time, you may hear a faint bubbling sound and/or see a bulge in the sand.
  3. Eventually melted wax will break through the sand, rise, and solidify as it enters the cool water. See Fig. 5. As with a real volcano, the process can be unpredictable. If after 5 min the wax has not broken through the sand, increase the hot plate temperature.


    Figure 4   Wax breaking through sand Figure 5   Wax solidifying in water
    Figure 4   Wax breaking through sand. Figure 5   Wax solidifying in water.



  4. When melted wax stops breaking through the sand, turn off the hot plate.
  5. Allow the beaker and hot plate to cool for 20 min.
  6. Once the beaker has cooled, remove it from the hot plate and thoroughly clean it. Sand, water, and wax may not be reused.

Discussion

While you are waiting for wax to melt and break through the sand, discuss what is happening inside the beaker and how it is similar to the formation of a volcano. As the temperature increases, a pocket of melted wax forms (magma chamber) beneath the sand (crust and/or lithosphere). As temperature increases further, pressure does as well. The melted wax expands and begins to push up into the layer of sand. When the melted wax (magma) breaks through the layer of sand it comes gushing out into the water (volcanic eruption of lava). Note: If the volcanic eruption is occurring over land, the water represents the atmosphere. If the volcanic eruption is occurring underwater, the water represents the ocean and the air above it represents the atmosphere.


Extension activities

  1. Research where volcanoes occur, the different types of volcanoes, and the conditions that characterize each.
  2. Cut an apple in half. Have the students compare the layers of the apple and the layers of the earth. Use toothpicks and masking tape to label corresponding features.
  3. Research the thickness of each layer of Earth's interior. Use proportions to calculate measurements scaled to fit on a piece of paper. Draw a scale model on paper using a ruler and compass.

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