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VOLCANOES (variation of this in gems)
This lab is an exploration of volcanoes. Students will discuss the properties of volcanoes.
Students will observe a replication of a volcano and watch how the different types of “lava”
behave.
Materials: Note—make the volcano plenty of time in advance and practice exploding at
home!
Wheat flour
Baking soda
Food coloring (red, blue, green)
Vinegar
Volcano
I made mine from plaster of paris with a hole to fit a cup down into. I would pour the
ingredients in the hole and let them explode out. This was actually quite a chore to make.
If you come up with a better volcano, let me know. You also need to think of the logistics
of cleanup.
Igneous Rocks box
Minerals box
Hand lens
Slide of volcanoes from Plate Tectonics gems guide
Invitation:
1. How many of you have ever seen a volcano? Can you think of any names of volcanoes?
What can you tell me about how volcanoes form? Do you know anything about how they
are related to plate tectonics? What are some ideas?
2. Who can remember what makes an igneous rock intrusive? How does is form? Can you
see the crystals? How about an extrusive rock?
3. Do you think volcanic rocks are intrusive or extrusive? From what we learned yesterday,
do you think you would be able to see the crystals easily in a volcanic rock? No, you
can’t see most of the crystals in an extrusive rock.
4. Does anyone remember the names of any extrusive igneous rocks—rocks with few
visible crystals? Rhyolite, basalt
5. All volcanic rocks are extrusive, but do rhyolite and basalt look exactly alike? What
looks different between them? Color
6. Why do you think they are different colors? They are made of different minerals
7. So even though all volcanic rocks are extrusive, they may be made up of different
minerals. Can you think of any ways this could affect the volcano they create?
1
Exploration:
1. Let’s look at our igneous rocks. Take out a granite and a rhyolite. Which one is the
volcanic rock? Rhyolite
2. They both have the same minerals (they came from the same type of magma), but they
cooled at different rates. Look in your mineral box. What minerals do you think are in
rhyolite and granite? Quartz, orthoclase, biotite, some plagioclase but not much mostly
light minerals.
Calcite is also a good guess, but it is generally not an igneous mineral. The minerals in quartz
and rhyolite have a lot of a compound called silica- SiO2. The mineral quartz is made entirely of
silica.
3. Ok, lets do the same thing with the basalt and gabbro. They are about the same
composition but, again, they cooled at different rates. Which cooled faster? Basalt
4. What minerals do you think are in gabbro and basalt? Amphibole, plagioclase, sometimes
biotite, and other dark minerals. These minerals don’t have much silica in them.
We are going to make mixtures that act like lavas today. We will make two lavas of different
compositions and observe their properties. One will be light with granite/rhyolite minerals that
are silica rich. The other will be dark with gabbro/basalt minerals that are silica poor.
Make two lavas
One dark (mafic)
Put 1 tbsp baking soda in volcano. Mix one drop of each red, blue, and green food
coloring and 1/2 c. vinegar in separate cup. Pour into volcano.
1. What observations can you make about that lava?
One light (felsic)
Show wheat flour. This wheat flour represents the silica. Let’s see how it makes the lava
behave. Put 1 tbsp wheat flour and 1tbsp of baking soda in volcano and stir. Mix one
drop red food coloring and 1/2 c. vinegar in separate cup. Pour into volcano. This
should make a more viscous (less runny) lava.
2. What did you observe about this lava?
3. Think about how long it took for each lava to break through the volcano top and pour
down the side. Did both lavas take equal time?
4. So the minerals that make up lava can change the properties of that lava. Which lava was
thicker?
2
Concept Introduction:
The light (felsic) one was thicker. Rhyolite lavas have lots of silica. They are very thick so they
don’t flow well. Geologists call thickness viscosity. If lava is thick, they say it is viscous.
1. Which lava was thinner, or less viscous? Basaltic lavas have very little silica. They are
thin so they flow easily. Most lava flows that you have seen on TV were basaltic lavas.
2. How might this affect the shape of the volcano?
3. Think about how volcanoes form. Where do the first rocks come from to give the volcano
its shape? They are all made from lava that has pushed its way to the surface broken
through earlier rocks. So rocks on a volcano were formed by lava exploding out from
beneath the crust.
4. If the lava coming out is runny, or less viscous, what will the shape of the volcano be
like?
5. Show slide of two volcanoes. Which one was formed by basalt, dark (mafic), less viscous
lava? Mauna Loa
6. Which one had more silica in it? Mount St. Helens is made of rhyolite—formed from a
light (felsic), viscous lava with lots of silica.
So the composition of the lava plays an important part in determining the shape of the volcano.
Volcanoes like Mauna Loa that are made of basalt are called shield volcanoes because of their
broad shape. Mount St. Helens is made of rhyolite, which has more silica and so is more viscous.
Ryholite doesn’t flow as well, so the volcano has a taller, more pointed shape. This is called a
strato volcano.
Application:
1. Looking at your rocks, which volcano would be darker? Mauna Loa because is made of
dark lava which has less silica. We know this because of the shield shape of the volcano.
(To lengthen the lesson you can go into why strato volcanoes are often found at plate boundaries
(subduction boundaries) and shield volcanoes are usually formed from hot spots).
Assignment:
In your own words, write what you have learned about igneous rocks and volcanoes in the last
two days. I will write some words on the board and you can use them in your paragraph if you
choose. You can also use the names of minerals in your box and draw pictures if you would like.
Igneous
Intrusive
Basalt
Gabbro
Lava
Mantle
Strato Subduction
Shield Hot spot???
3
Extrusive
Volcano
Viscous
Granite
Rhyolite
Magma
Crust
Plate boundary
Plate tectonics
Silica
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