Plate Tectonic - Volcanoes (3)
Post Lab 

  • Discussing that volcanoes erupt on the Earth's crust and produce new rocks.
  • Learning that volcanoes may produce different types of rocks.
  • ash
  • basalt
  • granite
  • lava
  • magma
  • obsidian
  • pumice
  • volcano
  • samples from previous lab
  • granite samples
  • worksheet

Students complete a worksheet and look at samples.

Mt. Saint Helens erupting in 1980


In order for the students to understand igneous rocks, they will need to know two factors that influence what type of rocks a volcano will produce. First, the manner in which lava cools will determine many different aspects of the igneous rock that will be produced. Second, the original chemical composition of the parent magma will play an important role in the formation of the igneous rock. It determines the mineral content of the rock. Remember, minerals make up rocks.

  1. Hold up different kinds of igneous rocks for the students to examine. Be sure to use a slow cooled rock (granite) and one or more fast cooling ones (any of the other samples). Ask the students which rock cooled inside the Earth. They should answer granite. Ask them whether the melted rock or magma (inside the crust), produced different rocks. They should answer yes, because the granite looks different, especially in mineral content.
  2. Show the students the rock samples that they examined in in the lab. Instruct students to predict which one of the three rocks cooled the fastest. The pumice and obsidian cooled before the basalt. Ask them how they know. The basalt has tiny mineral crystals, the pumice and obsidian do not. Remember that the quicker a lava flow cools the less time there is for minerals to form.
  3. Volcanoes are very interesting to students. You may want to have the books or other resources available for students to obtain more information. Here are some recommended websites:
    This site has good pictures, including a simulated 3-D column of ash erupted out of a volcano.
    Information on currently erupting volcanoes around the world, with links to each site. 
    University of Michigan volcano sites around the world.
    Excellent information on US volcanoes, as well as plate tectonics and geologic hazards. Go to the section on volcanoes.
  4. Have the students complete the worksheet. It may also be used as a test.

    Answers: (1) lava; (2) magma; (3) volcano; (4) obsidian; (5) pumice; (6) Hawaii; (7) Mt. St. Helens; (8) granite; (9) basalt; (10) ash

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