Learning the Shapes of Volcanoes

BACKGROUND:

The Plate Tectonic Cycle focuses on how data from volcanoes and earthquakes helps us to understand the Earth. Children are fascinated with this subject, mainly because of what we call the "disaster factor." Disasters of all kinds seem to captivate children's attention, especially those with death and destruction. Plate Tectonics is a subject with all these factors. As a teacher tells stories, we have found that students will remember a specific volcano or earthquake more if you include how many people died, how they died, and a visual look at the extent of the disaster without bodies.

Volcanoes form when molten rock, created inside the crust or upper mantle of the Earth, moves upward and erupts on the Earth’s surface. Molten rock is less dense than the surrounding rock, so it is buoyant and rises, just like hot air. Each eruption can produce layers of lava that will later become volcanic rock. These layers build the volcano. Depending on how viscous the lava is will depend on the shape. The word "viscous" is explained in the storybook called "Lucy Lava."

Volcanoes have several shapes, which are controlled by the composition of the magma and the nature of its eruption. If a volcano produces very fluid lava (low in the compound SiO₂, or silica), the magma flows a long distance before it cools, making a flat, shield-shaped volcano. If the volcano produces very sticky magma (high in silica) it tends to have an explosive eruptive style that includes lava, pyroclastic flows, and ash. This material piles up right around the volcano, forming a steep cone, a classic volcano shape. Volcanoes that are a built from ash and cinders usually have steep sides, but tend to erode quicker than volcanoes built from lava.

PROCEDURE:

Review that a) all mountains are not volcanoes and b) volcanoes produce one type of igneous rock (volcanic rocks). Students will learn that all volcanoes have just a few shapes, and volcanoes grow from the inside outward. Ask students if they have ever seen a round volcano (they should answer no).


Read students the storybook "Lucy Lava." You may want students to read each of the pages. Make sure that students understand some of the analogs. Question the students at all times to make sure they understand the words. Use the frame on "viscous" to illustrate how slow a viscous layer takes to spread.


Show students pictures or videos of volcanoes. You may use the pictures enclosed or pictures of volcanoes. Display them for your students, so that they can see the many different types of eruptions and shapes of volcanoes. You may want to glue them on tag board, so that you can display them for the next few weeks. If you don't have access to pictures, use library books or the Internet. You may want to tell students where the volcanoes are from, and locate them on a world map or a globe. Here are some recommended websites

http://www.geo.mtu.edu/volcanoes/
University of Michigan volcano sites around the world.

http://www.usgs.gov
On their search, type in volcano.


Draw the shapes below on the board.

Ask the students which shapes a volcano can take. Ask them why only A, B, and F can be real volcanoes. Discuss that lava can be a thick (viscous) liquid (like honey) or it can be very fluid like water, and that this is the main control on the shape of a volcano. You may say that the thickness (viscosity) of the lava depends on what chemical composition (ingredients) the lava is made of, and how hot the lava is when it erupts at the surface. When it comes out of the ground it flows and builds a mountain-shaped structure. The thicker (more viscous) the lava the more mountain-like it is, like in A and F. Examples include Mt. St. Helens and Mt. Lassen. The thinner (less viscous) the lava, the more the mountain will look like B. An example would be one of the Hawaiian volcanoes. The shape of a volcano is also determined by gravity, and the stability of the walls of the existing volcano.

Students do not need to understand the why or how volcanoes have different shapes, just that there are just a few characteristic shapes of a volcano. During the lab the students will experiment with different types of shapes from different viscosities.


OBJECTIVES: Learning the shapes of volcanoes. Discussing why volcanoes only have a few shapes. VOCABULARY: lava magma mountain shape volcano viscous MATERIALS: pictures or posters of volcanoes books on volcanoes (optional) world map or globe Lucy Lava by Michael Doherty	Students look at the different shapes of volcanoes.
	Molten lava that is very fluid.