This activity aligns with the following National Science Education Standard: Content Standard D: Earth and Space Science–Structure of the Earth System
Your students may well be familiar with some of the cave formations illustrated on the poster. And they may understand how the seepage of water through rock leads to the development of stalactites and stalagmites. As the water moves through the rock, it dissolves small amounts of limestone or calcium carbonate. When it drips from the cave ceiling, small amounts of limestone are left behind, eventually creating an icicle shape— a stalactite. Limestone that drips onto the cave floor builds up and forms a stalagmite.
Students can create their own stalactites and stalagmites to help them understand the process more clearly. (Note: Teachers can also be perform this activity as a demonstration.)
- Two jars—approx. 250 mL each (for each student group)
- Water—approx. 500 mL for each group
- Thick, natural fiber string (about 30 cm long)
- Cardboard—approx. 30 × 15 cm
- Epsom salts—about 2 cups for each group
1. Add equal amounts of Epsom salts and warm water to each of the two jars. Stir. Place the jars on the piece of cardboard about 15 cm apart.
2. Take the entire length of string and soak it in the solution until it is completely saturated—about one minute.
3. Place one end of the string in each of the two jars. Let the string hang down between the two jars, but do not let it touch the cardboard.
4. Leave the jars and the string in a location where they will not be disturbed for several days, but where students can observe the stalactites and stalagmites as they begin to form.
Adapted from Carlsbad Caverns National Park's Teachers Guide: "About Bats, Caves, and Deserts."