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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.
 
The video at the right 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 and increasing its density. When it is cooler and denser than the surrounding material, it sinks back down toward 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 hot spot islands. As the Pacific plate moves over the 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? This activity will provide show you how 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
 
Safety concerns: Be sure to keep all chemical, and glassware safety rules. As with all science lab activities, the most important safety rule is to follow all teacher directions.
 

Procedure:

  1. Pour a small amount of milk (<1 cm depth) into your Petri dish or bowl.
  2. Place a few drops 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.
 
Data: Describe and draw the results of your experiment. A sample video (long download) of the experiment is located on-line.
 

Analysis:

  1. Describe how this activity is similar to convection currents within Earth.
  2. How is this activity different from 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?
 
Review science lab safety rules here.

Get the plug-ins: Get Adobe Acrobat Reader and Get Quicktime Player. (The QuickTime plug-in is needed to play sounds and movies correctly.)

Want to share photos of you or your friends doing this activity? Send it in an e-mail with the following information:

  1. The title of the activity
  2. The URL (Internet address)
  3. Your name.

Remember that no pictures can be used that show student faces or student names on it. 

Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE Earth Systems Science core.

 


Updated October 24, 2008 by: Glen Westbroek

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