Taking A Look At Isostasy

~Taking A Look At Isostasy~

Problem

How does the Earth's crust float on the Earth's mantle?

Materials

2 blocks of wood: (1) 10cm x 10cm x 2.5cm; (2) 10cm x 10cm x 1.5cm
big bowl of water
metric ruler
25 metal washers

Procedure

1. Create a data table in which to record your measurements for block 1 and block 2. Make sure to include the number of washers and the amount of the wood above the water.

2. Label the larger block of wood 1 and the smaller block of wood 2.

3. Float block 1 in the basin of water. Using a metric ruler, measure the amount of wood above the water's surface. Record your measurement in your data table.

4. Carefully place ten washers on the surface of block 1. Measure the amount of wood above the water's surface. Record this information in your data table.

5. Continue adding washers two at a time. Carefully measure and record the amount of wood above the water's surface after each addition. Stop adding washers when the wood sinks or the washers spill into the basin of water.

6. Repeat steps 2 through 4 for block 2.

What Happened and Why?

1. Are there any differences in the way the two blocks of wood float before the washers are added? What happens after the washers are added?

2. Which block of wood is able to hold more washers before it sinks? Be sure to explain your answer.

3. How do the two blocks of wood resemble continental and oceanic crust?

4. How does the water represent the Earth's mantle?

5. If block 1 represents continental crust and block 2 represents oceanic crust, which crust is able to support the most weight?

6. How is the Earth's crust able to stay balanced on the mantle?

7. How does this investigation illustrate isostasy?

8. Design an experiment to examine isostasy in which thick mud is used to model the mantle. What do you think would be the results of your experiment?

Links

All About Isostasy