Lesson 3: Formation Of Underwater Volcanoes (3)

Lesson 3: Underwater Volcano Formation (3)
Explore Eruption Vidoes and Make a Volcano


Making and Mapping a Volcano

Explain: Oceanic crust spreads apart in areas called subduction zones, which causes rock in Earth’s mantle to melt. This creates a lava flow. Lava hardens into rock and builds up, layer upon layer, over time, forming underwater volcanoes, or seamounts. This process takes millions of years. Divergent boundaries are where tectonic plates move away from each other, resulting in the seafloor spreading. You can see evidence of this on maps that show mid-ocean ridges. It is in these rift zones that you are most likely to find seamounts. Most of the world’s volcanoes are underwater.

  1. Start by showing "Undersea eruptions caught on video" using remotely operated vehicles (ROV)  at the West Mata volcano off of Samoa and another in the Mariana Arc (Brimstone Pit).
  2. Cut off the bottom 1-2 cm of the paper cup and place at the center of the graph paper to make a circle. The cup and circle represent the crater inside the volcano.
  3. Tape the paper to the cardboard for stability. Label North, East, South and West on the graph paper after it’s taped to the cardboard.
  4. Fill the bottom cut portion of paper cup with baking soda. Then slowly pour enough vinegar to make the mixture foam up and flow out of the cup. This simulates the volcano’s eruption with lava flowing out.
  5. Use a colored pencil to trace around the edge of where the lava flowed out of the cup. Dab up the fluid with paper towel.
  6. Cover the area of “lava flow” with a thin layer of play dough. On the graph paper, use a colored pencil that matches the color of the dough to draw the shape of the lava layer. This is the start of a map that will show where lava flowed during each eruption of the model volcano. Pay attention to the cardinal directions.
  7. Repeat steps #5-7 three to four more times. Each time, put down new layers of lava “play dough” and then map it out by drawing/coloring the shape on the graph paper.
  8. Take core samples by cutting a plastic straw into thirds or fourths. Push the open end of the straw straight down through the play dough lava flows until you reach the bottom. Twist the straw in place and lift out a sample.
  9. Looking through the clear straw, you can see the layers underneath the surface of the volcano. Use this to investigate how the layers of the volcano formed over time.
  10. Compare all of your classmates’ maps and discuss how volcanoes form and how lava flows. 

Check for Understanding (formative assessment)

Use the Two Minute Paper (print as an exit slip or convert to Google Form) Two Minute Paper for Underwater Volcano Formation to check for understanding Or, ask: How do underwater volcanoes form? Where are you most likely to find seamounts? What type of tectonic plate boundary plays a role in the formation of new ocean crust and seamounts.


Undersea Eruption Caught on Video
Eruption at Brimstone Pit, Mariana Arc
Making an Underwater Volcano
Two Minute Understanding