BACKGROUND:
Volcanoes can help students learn about the formation
of the Earth’s 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: don’t 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:
- 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
