Download Name_____________________________________ Honors

Name_____________________________________
Honors Geology: Isostasy Lab
Background: Isostasy is a term used in to refer to the state of gravitational equilibrium between
the Earth’s lithosphere and the asthenosphere
1. Measure a block of redwood. Length=________cm, Width = ______ cm, Depth = ________ cm
2. Volume of redwood block = _______
3. Density of redwood block = ___________
(hint: use proper units)
4. Do the same for the block of oak.
a. Length__________, width__________ depth___________ volume__________
b. Density____________
5. What is the density of water?_________
6. Which block will float higher the redwood or the oak?_____________
7. Float both blocks. Was your answer to the above correct?________
8. Measure the distance below the water line the redwood block floats. ________ cm
9. Measure the distance above the water line the redwood block floats ________cm
10. Add a second redwood block to the first. Measure the distance below the water line that the
double redwood block floats. ________ cm
11. Measure the distance above the water line that the double redwood block floats. ________ cm
12. Did the block get heavier by the addition of the second block ?___________
13. Did the block get denser by the addition of the second block?___________
14. Is the ratio of height above/height below water line the same for the single block as for the
double block?
Single block ratio =
double block ratio=
15. Would you expect the single block of oak to have a larger or a smaller ratio than the single block
of redwood?_______________
16. Which block represents the granite continental crust and which represents the basalt oceanic
crust?
17. Push the two blocks toward each other in a collision course in the water. When they collide,
one block can move below the other more easily than the reverse (the process is called
subduction). Which crust (block) subducts?
18. What happens to the block when you place a few washers on top of it?
19. What happens when the washers are removed?
20. Part of the mantle, called the asthenosphere, behaves plastically, that is, it slowly changes
shape. The rigid upper mantle and the crust “floats” on top of the weaker asthenosphere.
Would you expect the asthenosphere to be denser or less dense than the crust?___________
21. Juneau Alaska is surrounded by glaciers that were much larger during the last Ice Age, which
was at its height 15,000 years ago. During the last century, the remaining glaciers have been
melting even quicker because of global warming. How would the melting of the glaciers affect
sea level?______________ Would that cause Juneau to rise or sink relative to sea
level?___________
22. Despite the change in sea level, the land near Juneau is rising almost 25 cm/year relative to sea
level. Why?
23. Would Juneau’s movement be similar to adding the washers or removing the
washers?_________
24. As mountains erode into the sea, would you expect the continent to rise or fall relative to sea
level?________________ Why?