Ch 20 isostasy, orogeny, mountain building Name ______8th Grade Earth Science Mrs. Krempa Date & Period ______

Use your textbook pages 561 - 576 to answer the following questions.

1. Topography: _____ variation in elevations of the crust ______

What does a topographic map show? _____ an area’s hill & valleys ______

2. Isostasy: the displacement of the Mantle by Earth’s continental & oceanic crust in a state of equilibrium

a. The crust and mantle are in equilibrium when the downward force of gravity on the crust is balanced (equal) to the upward force of buoyancy (float) on the mantle. (caused by the displacement of the mantle by the mass of the crust)

b. A good example of this concept (equilibrium) is when people get in and out of a small boat.

Explain: People get in a boat? Boat sinks deeper / displaces more water. People out of boat? Boat rises / displaces less water (people’s mass now out of boat). Similar to sinking and rising of Earth’s mantle depending on how much crust is sitting on it. Mountains = a lot of displacement, areas where crust is thin = less displacement

3. What is a “root”? (last paragraph on pg. 563) thickened areas of continental material that extend into the mantle below Earth’s mountain ranges

4. What purpose do mountain roots serve? Counterbalance the enormous mass of the mountain range above Earth’s surface

5. Isostatic rebound: slow process of the crust rising as the result of the removal of overlaying material

a. In the process, mountains are _____ eroded ______over hundreds of millions of years,

while the crust below them ______rises ______. (weight of mountain being taken off of crust, crust can now expand back up – isostatic rebound!)

6. Orogeny: ______all processes that form mountain ranges ______

7. Divergent-Boundary Mountains

a. These underwater volcanic mountains form a continuous chain the snakes along Earth’s ocean floor

b. As a result of the decrease in density of the new oceanic crust as it cools, contracts and subsides,

the crust stands highest ______where the ocean crust is the youngest______and

makes the underwater mountain chains have ______gently sloping sides______

8. Uplifted Mountains

a. Form when: _____ large regions of Earth have been slowly forced upward as a unit ______

b. Have rocks that undergo: ____ less deformation than other building processes ______

c. Are the result of (popular hypothesis): a part of the upper mantle (lithosphere) cools, becomes dense & sinks into the underlaying mantle. This “chunk” of cooled mantle provides buoyancy & vertical lift for the crust on top – making a “bulge”.

d. Examples: ____ Sierra Nevada Mountains (in CA), Colorado Plateau______

9. Fault-Block Mountains

a. Form when: faults lift & stretch the crust and large pieces of crust are dropped downward due to tensional forces

Explain: When Earth’s crust is stretched… ____ a series of normal faults can form ______

b. Are not necessarily associated with ____ plate boundaries ______

c. Examples: Basin & Range Province (SW USA & Norther Mexico) Grand Teton Mountains (WY)

d. Some of these mountain ranges consist of hundreds of nearly parallel mountains separated by normal faults