Making a "Solution" Cave
activity exercisedemonstrationsuggested grade levels: 4-8

view Idaho achievement standards for this lesson

Solution caves are formed by slightly acidic ground water circulating through fractures in limestone. Even slightly acidic water is capable of dissolving great quantities of this soluble rock. As time passes, the openings become larger and larger until they may be large enough for a man to pass through. This simple experiment will let students observe a process that normally takes many, many, years in real life. It is a fun activity for students and it encourages them to work together.

Scissors Clear plastic bottle, such as a small bottled-water container Piece of aluminum foil
Large nail Glass bottle or jar with an opening larger than that of the plastic bottle 5 cups (725 g) of sand
Rubber band 1 cup (200 g) of granulated sugar or sugar cubes 1 cup (236.6 ml) of warm water
Spoon or trowel    

Use the Caves section of the Digital Atlas of Idaho. To get there: Click on Idaho Overview, then on Caves. Read through the cave section and click on the links to see the pictures. This should serve as an excellent review on caves. It also provides a description of how solution caves form. Review as a Class:

1. The 3 basic kinds of caves found in Idaho.
2. The different processes by which these kinds of caves form.

Activity: (Can be done as a demo if supplies are limited)
1. Cut off the bottom half of the plastic bottle. Remove the cap.
2. Fit the piece of aluminum foil over the opening of the plastic bottle and Hold it in place tightly with a rubber band. Use the nail to punch a few small holes in the foil.
3. Place the plastic bottle inside the opening of the larger glass bottle so it can act as a funnel.
4. Put a 2-inch (5 cm) layer of damp sand in the plastic bottle. Press it down so there are no air spaces.
5. Put a 1-inch (2.5 cm) layer of sugar or sugar cubes on top of the sand. Be sure it is pressed against the side of the bottle and filled in solidly. The sugar represents limestone under the ground.
6. Put another 2- or 3-inch (5 or 8 cm) layer of sand on top of the sugar. Press out all spaces. You should be able to clearly see three layers.
7. Pour 1/2 cup (118.3 ml) of warm water on top of the top layer of sand. Wait until it drains down, and then pour the other 1/2 cup (118.3 ml) of water. Watch what happens to the sugar (the limestone) after two or three hours. What has caused the caves that you see? What does this show you about how caves might form underground?

Handout/Activity links:
These are links to access the handouts and printable materials.

Related Lesson Topics:
Geology: Geology Topics

Lesson plan by Alan Anderson, Gwen Diehn and Terry Krautwurst with permission from Geology Crafts for Kids, 2001
Idaho Achievement Standards (as of 7/2001) met by completing this activity: