Mountain in the Sea

Instructional Objectives
Background Information
Extension for Lower Grades

Topic: Convection Currents

Instructional Objectives:

Students will:

  1. Learn how cold and warm water behave in the marine environment due to convection currents.
  2. Conduct an experiment to demonstrate the formation of a convection current.

Background Information:

Around the steeply rising sides of Cocos Island's submarine mountains, cold waters from the depths often flow upward to mix with warmer surface waters. This upwelling, as it is known, is due to swiftly moving currents under the water as well as on its surface.

When there is no upwelling, what prevents colder waters from ordinarily mixing with warmer waters? When you enter a swimming pool, for example, the warmer water always seems to be at the surface, with cooler water underneath. This is due to the fact that, like warm air, warm water is less dense and therefore rises to remain on top of cooler, denser water.

Activity: Create a Convection Current

Time Needed for Activity: One 45-minute period

Target Grade Level:High School


  • one baby-food jar
  • two 24-inch-long lengths of string
  • blue food coloring
  • one additional container large enough to hold the baby-food jar, and filled with warm water


  1. Fill the baby-food jar with ice water and a few drops of blue food coloring. Tie the strings to the jar's neck and lower it into the container full of warm water. Keep tension on the strings while you lower the baby-food jar all the way to the bottom. Observe what happens.
  2. Repeat, this time filling the large container with ice water. Fill the baby-food jar with very warm water and add a couple of drops of blue food coloring. Again, using the string-suspension method, lower the jar into the large container all the way to the bottom. Observe what happens.
  3. Note how, when you lower the colored ice water into the warm water, the ice water remains in the baby-food jar or close to it, settling to the bottom. In the second step, note how the colored warm water rises to the surface of the large container.


Warmer water tends to rise above cooler water. In the ocean, cooler waters sink and warmer waters rise toward the surface. The movement of water at various temperatures helps create currents within the water column. These convection currents, as they are known, were caught on film during the program as mirage-like images.

Consider the similarity between this phenomenon and a desert mirage, in which images at a distance are blurred when viewed through the varying densities of warmer and cooler air layers.

Extension for Lower Grades:

Carefully pour heated water into a large, clear container (such as a classroom aquarium) filled with cool water. Observe the reaction as the fluids of greatly differing temperatures mix. Record your results. Now, attach an image such as a large color photograph of a fish or other marine animal to the back side of the aquarium, and repeat the mixing experiment. Note the effect that the mixing fluids have upon the image. Is it similar to the images seen in the program? Why? What is taking place?

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