GOL 111 Investigations 2A (LAB)

7. Note in Figure 2 the red arrows denote tectonic plate boundaries and their motions along the western margins of South America, Central and North America, the Aleutian Islands, and beyond. Except along the U.S. West Coast, the arrows evidence the forcing of the ocean floor under another plate (forming a subduction zone) as tectonic plates ____.

A. convergent

10. Within the abutting plates along the Mid-Atlantic Ridge, the crust migrates away from the ridge as new material is added. (Imagine two treadmills positioned end-to-end with their treads moving outward in opposite directions.) From the Mid-Atlantic Ridge westward toward the east coasts of Greenland and North America, the age of the oceanic crust ____.

A. increases

12. The nearby continental topography in the image indicates the possibility that mountain building ____ associated with this plate boundary.

A. is

9. Lava wells up along divergent plate boundaries from Earth's interior, then cools and solidifies, adding new oceanic crust to a plate's edge. The existence of Iceland, a volcanic island along the Mid-Atlantic Ridge, ____ geological processes known to operate at divergent plate boundaries. Iceland's Eyjafjallajokull Volcano, made famous by its eruptions in April 2010 that produced ash clouds and closed many European airports downwind for days, is located on the Mid-Atlantic Ridge.

A. is consistent with

13. Compare the image with Figure 3. This comparison shows that earthquake activity along the west coast of South America is primarily on the ____ side of the trench. This is consistent with a convergent plate boundary where a denser oceanic plate is being subducted under a continental plate composed of less dense material.

A. land

3. Ocean bathymetry can be examined in more detail on regional views prepared by the NOAA National Centers for Environmental Information (NCEI), formally name the National Geophysical Data Center (NGDC). Click Link 2A-2. This Mercator projection allows one to examine regional views. Click on the Gulf of Mexico to center and enlarged the U.S. in the view. Compare the ocean bathymetry off the eastern and western coasts of the coterminous U.S. In general, the color coding shows that ocean depth increases more rapidly moving away from the U.S. ____ coast

A. west

8. Referring back to Figure 2, the red arrows denoting movement indicate the plate to the west of the Mid-Atlantic Ridge is moving generally ____ while the plate to the east is moving in the opposite direction

A. westward

14. Geologically, coasts are generally either tectonically active (near a plate boundary) or passive (site of mostly sediment deposits). The west of South America is tectonically ____, while the east coast of North American is not.

B. active

1. Survey the ocean bottom relief in the two Figure 1 views which show primarily the bathymetry in the Atlantic and Pacific Ocean basins. Color coding denotes water depth, showing that ocean depth increases as shadings of ________ become darker. [Note that land topographical relief is also displayed. Land elevation increases as green colors become lighter and then browner.]

B. blue

6. Ocean trenches are deep, elongated depressions on the ocean floor formed along convergent plate boundaries where the edge of one crustal plate has been forced under the edge of another plate (the process is called subduction). According to Figure 2, a plate boundary extends along the west coast of South America. Return to the enlarged NCEI map where you had been viewing the Mid-Atlantic Ridge. Use the horizontal and vertical sliders to center the map view on South America's west coast. The color-coded bathymetry (darkest blue being deepest) reveals an ocean trench deepest off the ____ portion of South America's western coast.

B. central

15. In the NOAA animation, the age of the crust is color coded with red being the youngest. It can be seen in the movie that the youngest ocean-bottom crust is associated with ____ plate boundaries (for example, the Mid-Atlantic Ridge).

B. divergent

5. Oceanic ridges are underwater volcanic mountain ranges formed at diverging tectonic plate boundaries. Geological evidence indicates that the landmasses on either side of the Atlantic Ocean were once joined together as one super-continent, known as Pangaea. The Atlantic Ocean basin was formed when Pangaea split apart. The volcanically active Mid-Atlantic Ridge is marked in Figure 2 with red arrows denoting motion that identifies it as a ____ plate boundary.

B. divergent

2. Examination of the Atlantic and Pacific Ocean basins indicates that the ocean floor generally ____ flat and featureless

B. is not

4. Study the Mid-Atlantic Ridge. Its lighter blue color shading indicates the ridge is at a generally ____ ocean depth compared to the surrounding ocean farther from the ridge. However, along the center of the ridge is a nearly continuous dark line representing a deep, narrow central rift valley that forms above tectonic plates which are separating. Seen in the view are other dark lines, aligned nearly perpendicular to the ridge and rift valley, but generally parallel to each other. These ocean valleys are associated with fracture zone (now inactive) related to differences in spreading rates.

B. shallower

11. Return to the NCEI map and to the west coast of South America where we earlier examined the narrow zone paralleling the coast where the ocean floor is exceptionally deep. This ____ marks a convergent plate boundary

B. trench