Caves

Many caves form because weakly acidic groundwater flows through cracks in limestone and slowly dissolves the rock. Caves form particularly well in areas where there is a resistant caprock like sandstone over the limestone below. In this activity, you will compare the solution rates of different minerals in liquids of differing pH to discover for yourself how some caves form. Note: It may take a week or longer to complete this activity.

Materials

9 large disposable plastic cups (12 oz or larger)

3 pieces of chalk (limestone)

3 quartz pebbles

3 small pieces of broken concrete

Bottle of vinegar

Bottle of clear ammonia

Pure water

9 self-stick labels or

Masking tape

Marking pen

Pen and paper

1. Fill three cups half full with vinegar and label them "acid." Fill three cups half full with pure water and label them "neutral." Fill three cups with 1cm of ammonia and 5 cm of water. Label these "base." (Note: Ammonia from the bottle is too concentrated to use without dilution. Be careful because even diluted, it can irritate skin and eyes.)

2. Examine and describe each of the rock samples in as much detail as possible. Set up a data sheet for each sample and record your first observations under the heading "time zero." Make sure to include things like color, texture, size, and shape.

3. Place one piece of chalk in a cup with vinegar, a second in a cup with water, and the last in a cup with ammonia. Add the word "chalk" to each label. Repeat the procedure with the concrete and quartz pebble so that each cup now has a rock sample in it.

4. Place all nine cups in a dark corner and observe them the next day. Record any changes you see for each sample under the heading "day 1." Continue to make observations for each day until a full week has passed.

Questions

Based on your observations, what can you say about the behavior of limestone in the three different chemical environments?

Did any of the other samples show the same type of behavior? How might these similarities and differences help to explain how caves are formed?

Based on your observations, what material is used to help hold concrete together? What effect would acid rain have on structures made from concrete?

Some of the best archaeological evidence comes from caves. Bones, pottery, and even food remains often are found in caves, some dating back more than 50,000 years. What aspects of a cave environment make it so good at preserving the past? Why were ancient hunters and gatherers drawn to caves?

Erosion by acid solutions is only one way that caves form. Other environments include empty lava tubes near volcanoes and ice caves in glaciers. What do these different cave types have in common? Use materials found around your home to model the development of different types of caves.

Write a story about what it would be like to live underground. How could you adapt to living in a cave environment? Where would you get your food? What about air and water sources? Is light critical to human life? How might you cope?

Newton's Apple, http://ericir.syr.edu/Projects/Newton/index.html