COMPETENCIES: Observing; visualizing; writing; nature of scientific activity; models and scale; space and dimensionality; change; data; resourcefulness and creativity; becoming a productive group member; consistent, responsive, and caring behavior; rights and responsibility of self and others; conceptualizing; critical thinking; developing new knowledge; and expanding existing knowledge.
OBJECTIVES: The students will be able to: 1) work productively in small groups to make a cave 2) conceptualize how water carves or creates caves.
MATERIALS: Modeling clay (4 oz. per student or group), sugar cubes (3-6 per cave), warm water, see-through bowls (1 per student or group).
BACKGROUND: The two basic kinds of rocks found in the Round Spring Cave area are limestone and sandstone. (The type of limestone at Round Spring is also known as "dolomite.") Limestone is the "soft" rock (more water soluble) that is dissolved more easily by water. Sandstone is the rocks that are on top of the cave. It is "harder" (less water soluble) and doesn't let the water soak into the cave. The limestone was laid down in this part of Missouri around 450 million years ago. A shallow, warm inland sea covered the land. As the animals that lived in that sea died, their hard bodies (shells) fell to the bottom of the ocean. With time and pressure, the shells compacted together to form limestone. The limestone in this area is between 700-1200 feet thick. After many years of deposition, the sea receded, as the continent slowly drifted north.
1. The teacher asks the students what it takes to make a cave. The teacher writes the students' answers on the blackboard (rocks, water, time, etc.).
2. The teacher then explains that there are two types of rock that make up Round Spring Cave. One, called limestone, is softer and easily dissolved by water. The second is harder and is on top of the limestone. Since it is harder it is a good roof to the cave, protecting it. This harder rock is sandstone and shale. It takes a lot longer for water to dissolve this sandstone caprock.
3. The teacher passes out a lump of clay to each student ( or each group of students, approximately 4 oz.) The clay will be the sandstone in our model. The teacher also passes out 3 or 6 sugar cubes, to make different sized caves. The sugar cubes will be the softer limestone in our model.
4. The students flatten their clay out into a "pancake." Then they should place the sugar cubes on the clay, so that each cube touches the other, and with at least one cube touching the edge of the clay. Then the students wrap the clay around the sugar cubes, forming a ball. The students need to make sure that at least one sugar cube is exposed or that there are some cracks ("fissures") in the clay layer. Students can poke holes in the clay with a tooth pick to simulate porous rock.
5. "Now that we have our rock layers, what do we need to turn it into a cave?" The students should respond "water." Each student or group should have a small see through bowl, (cutting the top off 2 liter bottles works well). Instruct the students to put their cave in the water. The students should observe what happens. Squirt bottles make this more fun, but a simple cup will work as well.
6. The students may observe:
7. The class groups back together and notes their observations on the board.
Closure: We have made models of a limestone cave. For natural places like caves to form we know it takes a long time and the right ingredients. That is why we need to take care of our special natural places.
1. A follow up activity could be to make rock candy and talk about how that relates to the formations found inside the cave.
2. The class may want to visit Round Spring Cave to identify the differences between the sandstone and limestone while in the field.
3. The students could find other items that would dissolve in water, that could be models for the limestone, and other items that do not dissolve that could be models for the sandstone.