Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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 4