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Inside the Earth - Round And Round We Go!

Convection currents of magma within Earth are thought to be the mechanism that moves the continental and oceanic plates around on the asthenosphere. These forces and motions are occurring deep within Earth. It is unfortunate that we will never be able to take a field trip to see how it all works.

This video models what a convection cell would look like if we could dig a big hole and have a look. The fumes rising on the right side represent the magma heated from the core. It rises up until it reaches the solid crust. As it rises, it starts to cool, condensing it and increasing its density. When it is cool and more dense than the surrounding material, it sinks back down towards the core, where it is reheated and the process can start over again.

This is another model of what happens at a hot spot. Some volcanoes are formed far away from subduction plate boundaries. Magma rising through the oceanic crust will form an active seamount. If it keeps growing and breaks the surface of the water, an island is formed! The Hawaiian island chain is the most famous mantle plume (hot spot) islands. As the Pacific plate moves over the mantle plume (hot spot), over time the area of activity changes. Kauai was active 5.5 million years ago, and the big island, Hawaii, has active volcanoes now. Lo'ihi, a young and active seamount south of Hawaii, may be the next island in the chain.

Try It!
Problem: How can I model the process of convection? The purpose of this activity is to provide you with the opportunity to model the process in a format that will be easy to observe.

Materials:

  • Milk - either whole or 2%
  • Food coloring
  • Petri dish - a small bowl or dish will also work
  • Liquid detergent
  • Toothpicks

Procedure:

  1. Pour a small amount of milk (<1 cm depth) into your Petri dish or bowl.
  2. Place a few drops of your choice of food coloring at various places in the milk. (Don't drop the color in from too high or it will make a mess!)
  3. Pour a small amount of detergent onto the table or counter.
  4. Carefully dip one toothpick into the detergent
    • Make sure that only a small amount of detergent is on the toothpick.
  5. Lightly lower the detergent end of the toothpick until it touches the drop of food coloring.
  6. Record your observations.

Safety concerns: Be sure to follow all chemical safety rules that are specified by your teacher and in all general laboratory experiences. As with all science lab activities, the most important safety rule is to follow all teacher directions.

Data: Describe and draw the results of your experiment. Here is a sample video of the experiment.

Analysis:

  1. Describe how this activity is similar to convection currents within Earth.
  2. How is this activity different than Earth's convection cells?
    • What is missing?
  3. What part of the interior of Earth does the milk represent?
  4. What does the detergent model?
utah state board of education This Sci-ber Text was developed by the Utah State Board of Education and Utah educators.