Isostasy can be seen where the Earth's lithosphere (crust) presses down on the weaker asthenosphere )mantle) which, over deep geological time, flows sideways and down. (Analogy- large person getting into a water bed.)

Post-glacial rebound (sometimes called continental rebound, glacial isostasy) is the rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period, by a process known as isostasy.

Isostasy is the balance between the forces pushing down and the forces pushing up. (Greek íso "equal", stásis "standstill")

http://www.youtube.com/watch?v=4qAI2s1kdTs

http://www.youtube.com/watch?v=V7HP1jsoisE

http://www.youtube.com/watch?v=ibTWQogsbL8

The next slide is an “A” procedure.(Yes,….. I know graphics could have made it an “A+”!

• Question: Do continents and glaciers show Isostasy?

• Hypothesis: If Isostasy is the balance between gravity and buoyancy, then it should be able to be modeled using models of the earth’s ocean, continental and mountain crust and pennies.

• Materials: Beaker, Water container, 50 pennies, three wood squares representing the ocean, continental, and mountain crust thicknesses.

• Procedure:

• Step 1- Remove all materials from the lab basket and place them all separately on the surface of your Granite lab table. Start with the thinnest of the three boards representing the oceanic crust. (Check the label on the back of each of the squares.)

• Step 2- Use the beaker to fill the container labeled “H2O” container with 300ml of water and place in the center of the lab desk. Each of the blocks are labeled on the side that is red and looks

like it is molten, float the wooden squares so that landform picture is visible, and the red “molten” side is down.

• 3. Carefully place one penny at a time, head up, in the center of the wooden block representing the oceanic crust.

• 4. Record the number of pennies that each block can support before the block submerges and pennies slip off. Stop adding pennies when the wood sinks or the pennies spill into the water.

• 5. Repeat this procedure five times and throw out by drawing a line through the least and greatest values for each set of trials and then average the remaining three trials. Record this average

in your data table.

• 6. Repeat steps 2-5 for the medium thickness wooden block that represents the continental crust with a picture of Michigan on it.

• 7. Repeat steps 2-5 with the thickest wooden block that represents the mountain crust that has a picture of Mt. Everest on it.

• Observation Data:

• Conclusion: Isostasy is the balance between gravity and buoyancy. If this is correct then by adding pennies to the wooden blocks then they should become less buoyant and sink

further into the liquid they are floating in. We see this effect with Continents and when Glaciers

http://www.globalchange.umich.edu/globalchange1/current/lectures/topography/topography.html

Isostasy Wooden simulation Data Average number of pennies

Ocean Crust .6 mm

Continental Crust 1.1 mm

Mountain Crust 3.5 mm