Student Activities

What's that Green Stuff?!?!

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Grade Level:
Upper Elementary: Third Grade through Fifth Grade
State Standards:


Overview: Students will look at the real world challenges that rangers face while protecting the cave.

Objective: Students will identify sources of contamination and ways Rangers reduce these problems.

Materials: Photo set of Algae Reduction, 2 limstone rocks of similar surface texture, water, and dish soap

Background: The cave is impacted by visitors in a variety of ways.Two of the major ones are visitors unknowingly bringing in algae spores and leaving behind oily residue when they touch the cave. Algae, once deposited, begins to grow and the oily residue builds up over time.

There are a few ways rangers can mitigate the algae problem. One, probably the simplest, is to simple turn off the lights whenever possible. This mostly happens at night when there are no tours in the cave. This has the added benefit of reducing the electricity use. 

Second, the speed at which algae grows is dependent on the light source. For example, incandescent light bulbs put out a lot more heat than LEDs. In 2008, in order to lessen the amount of algae in the cave, Wind Cave replaced its entire lighting system with LEDs. This led to a substantial drop in algae growth, and the electricity bill, as well. Without the added heat of the incandescent bulbs, the relative cool of the cave inhibits algae growth.

A final way rangers try to stop algae is by directly spraying it with bleach water. A concentration between 20 to 50% bleach is used. Being as large colonies of algae can exist outside the public view, it is important to get off trail and wipe out these larger groupings. The existence of these large colonies, allows the algae to continue to spread along the tour route and into other lighted sections of the cave.

The oily residue problem can be diminished only with the help of visitors. When you are down in the cave be very careful not to touch the walls.  Our hands and skin contain oils that can be left on the rock by simply touching it. This oil not only damages the rock by discoloring it but also, since most speleothems depend on water to form, this coating of oil does not allow the necessary minerals to continue to deposit. It also gives food to the various algae and molds growing down there.

Method: 1. Take the two limestone rocks and wash them with a mild solution of water and dish soap. Rinse completely and allow to dry.

2. Introduce the topic and give PowerPoint presentation and discussion the problem of algae at Wind Cave.

3.  Have the students pass around the mirror and get everyone to touch the glass surface. Discuss what is on the mirror (dirt and oil).

4. Give rock demonstration. One rock should be left on your desk and students instructed that no one should touch this rock. Pass the other rock around the classroom. This rock should be constantly handled by the students. You can do this during the PowerPoint presentation.

5. Wind Cave National Park lets in about 100,000 visitors a year into the cave. Ask students what would happen if 100,000 people walked through their home every year and touched the walls. How many people is that if only 20% touched the walls. Ask if they think all that oil and dirt damages the cave? 

6. Give background information. Explain that at the end of the day we will compare the two rocks. Bring up the example of an oil spot on a parking lot and how water behaves on that. Have students discuss what will be the difference between the rocks. Discuss how we can clean a mirror but we don’t want to use harsh cleaners in a cave. Have students discuss why. 

7. At the end of the day, have students test the two rocks by dripping water on them. Which rock is water resistant? Have students discuss what happened and why. Is the “no touch” rule a good one? (If students hands aren’t dirty enough you can rub some oil onto one of the rocks)


Two rangers cleaning up the tour route. Bleaching any algae spots.

Download Pictures of Algae Reduction

Short explanations of what is happening in each photo

Download Notes for the photo presentation

Last updated: September 20, 2016