Plate Tectonic - Volcanoes (K)
Post Lab 

   
OBJECTIVES:
  • Discovering how volcanoes grow.
  • Comparing different types of eruptions
VOCABULARY:
  • cone
  • grow
  • volcano
MATERIALS:
  • cardboard sheet
  • paper cone cup
  • shaving cream or whipped cream in a pressurized can

Students observe how lava flows from a volcano.


A cooled Hawaiian lava flow

BACKGROUND:

Volcanoes can help students learn about the formation of the Earthís crust. We have found that some children associate the "blowing" up of a volcano as making it smaller. They have to be coaxed to understand that with each new lava flow the volcano will get larger. Students also need to realize that the shape of a volcano will depend on the pre-existing topography on which it erupts. A an eruption in a valley may fill up the valley before it ever builds a volcano. In addition, volcanoes will not be very steep (their slopes are usually less than 45o), because the magma is not thick enough (viscous) to "stand up" very high.

Volcanoes have many styles of erupting. Some are quiet, like the Hawaiian volcanoes, and other are explosive like Mt. St. Helens in Washington State. The violent eruptions usually are highly charged with gases, which cause magma to explode as they shoot out of the volcano. This is similar to the results of shaking a can of carbonated soda and opening it: donít try this inside!.

Volcanoes are hill- to mountain-sized. They are built by accumulation of their own eruptive products including lava (a flow of magma), and fragments of magma (bombs and ash). There are usually one or "vents" on the volcano that connect the reservoirs of molten rock inside the Earth (magma chambers) with the surface.

Volcanoes have a variety of shapes. Cone and dome shapes are most common, but volcanoes can also be flat. Small children need to see how these different shapes are created. Observing the development of shapes created by nature will help students to understand the growth of volcanoes.

In this activity the students observe the shapes formed by "eruptions" of whipped cream or shaving cream. The main concept is that the "cream in the can" represents the magma coming from inside a volcano. When it reaches the surface of the Earth, it is called lava. Lava comes out of the earth at different speeds, and forms mountain-like shapes.

We suggest you practice making volcanoes before you show the class. Controlling the pressure of the can is tricky.

PROCEDURE:
  1. Cut a small hole in the sheet of cardboard, and a hole in the top of the paper cone. Squirt the shaving cream or whipped cream through the holes, as shown in figure 1 and 2, to create a "volcano". Vary the pressure and duration to make different sized volcanoes. In Figure 1, you are having the students observe that a new volcano will build a dome or cone-like structure. In Figure 2 you are emphasizing that a cone-shaped volcano will continue to erupt a dome-shaped lava flow.
      
    Instruct students to guess the final shape the "volcano" will make.
    Discuss whether the shaving cream or whipped cream is thicker or thinner than real lava. It is actually both thinner and thicker: some magmas are very fluid, like flowing concrete, while others are very sticky, like cold honey
  1. After you have demonstrated the two "eruptions", ask the students if they believe the cream (representing lava) is "growing" or "getting larger". Explain that volcanic "growth" is different from "people" growth. Ask the students why the shape isn't turning into a ball or going straight into the air. Basically, the lava is liquid and wants to flow. It flows (because of gravity) to a "comfortable" position, which in our world tends to be in the shape of a low lying cone.

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