Please fill out and return this sheet after viewing Program #14.   If you are unsure of an answer, give your best intelligent guess.
 

1.  What features are often found at or near plate boundaries?

Mountain belts, volcanic chains, ocean trenches, earthquake zones

2.  What are the three major types of  plate boundaries?

convergent, divergent, transform

3.  Where can one see rifting of ocean crust on dry land?  Where can one see rifting of continental crust?

Iceland; East African rift

4.  What are three types of convergent boundaries?  What are some geographic examples of each?

ocean-ocean: Alaska (the Aleutian Islands), Pacific Plate v. N. American Plate
ocean-continent: Andes (Western S. American), Nazca Plate v. S. American Plate
continent-continent: Himalayas, Indian plate v. Eurasian plate

5.  Why doesn't continental crust subduct?

It's too buoyant; it's density is so light that it can't sink into the mantle

6.  Why does magma tend to form around subduction zones?

Ocean crust altered by seawater subducts into the mantle, where temperatures are high enough at a certain depth that partial melting of altered crust and mantle takes place

7.  What is a transform boundary?  What are examples of two types of transform boundaries?

a lateral fault (fracture) that usually offsets a segment of mid-ocean ridge; two types of transform boundaries: that found at the ocean floor  (fracture zones between segments of mid-ocean ridge), and that found on dry land (San Andreas fault)

8.  What is the difference between the lithosphere and asthenosphere?

The lithosphere contains the crust and the very upper layer of mantle.  Together these layers move as one unit in each tectonic plate.  The lithospheric plates migrate on top of a more plastic-behaving asthenosphere, which is also an upper layer of mantle, but below the lithosphere.

9.  What are two ways that rocks can deform in response to stress?

they can fold or fracture

10.  What are variations for the way mantle convection moves plates?
 
Plates may ride on top of mantle, carried piggy-back; plates may be pushed apart at mid-ocean ridges; plates may be pulled into the mantle at subduction zones

11.  What is the difference in the type of convection found in the mantle and in the outer core?

Mantle convection occurs in mostly solid rock.  Outer core convection occurs in molten liquid.

12.  What are hotspots (or mantle plumes)?

Focused areas where mantle material rises from deep toward the surface, where it partially melts and generates volcanic and geothermal activity at Earth's surface

13.  How did the Hawaiian Islands form?

The Pacific Plate migrated NW over the Hawaiian hot spot.  The hot spot (mantle plume) occasionally punched a hole through the ocean crust and erupted lava onto the sea floor, and eventually built up an island.  As the island migrated away from hot spot, the volcano was cut off from its source.  The hot spot meanwhile punched a new hole through the ocean crust and built up another volcanic island.

14.  Why do many islands that form from hotspots become flat-topped islands?

When a volcanic island is cut off from its hotspot source, then it quits growing and begins to erode down by surface water and wave erosion, and subsides below the water.

Chapter 19, pg. 493

#15.  Explain how plate tectonics can account for the existence of the mid-oceanic ridge and its associated rift valley, earthquakes, high heat flow, and basaltic volcanism.