Exercise 8: Plate Tectonics

Questions

1. If the Atlantic Ocean is widening at a rate of 3 cm per year, how far (in kilometers) will it "open" in a million years? In 200 million years?

   For some of the following questions you will need an atlas. The following map may help.

2. The Plate Motion Calculator will let you make some calculations that lead to a better understanding of present day plate motion. Use the following data and think about the implications. [For the following two problems use the Absolute Motion calculator.] If you would like some instruction then see the following exercise
   1. Obtain the longitude and latitude of UH (to the nearest degree or so will be sufficient). What is the velocity of the plate at this locality? Make sure you select the proper plate (North America) and read the directions for entering latitude and longitude. The direction East would be at 90 degrees, South at 180 degrees and West at 270 degrees; use this reference in interpreting the calculated "direction". Assuming that the velocity will be constant, how long will it take your location to move 1,000 kilometers (assuming that the direction of movement remains constant)?

      At about 30 degrees N latitude (Houston), the longitude of the mid-Atlantic spreading center is about 45 W longitude. What is the direction of the NA plate at this boundary? What is the velocity?

      The western boundary of the NA plate is about 120 W longitude at about 30 degrees N latitude. What are the velocity and direction of the NA plate at this location?

      Generalize .... what happens to the direction of the NA plate and its direction of movement going from its eastern to its western boundary at 30 degrees N?

   2. Santiago Chile is located at 30 degrees S latitude and 70 degrees W longitude. What is the velocity of the South American Plate at this point? The Juan Fernandez island on the Nazca Plate is located at 30 degrees S latitude and 80 degrees W longitude. What is its velocity?

   3. The South American Plate and the Nazca Plate are converging. Will the South American Plate "overtake" the Nazca and "sit" on top of the East Pacific Rise? Or, will the distance between the South American Plate and the Nazca Plate increase?

3. The faster the spreading rate, the wider the magnetic anomalies. Hot spots (such as the one in the asthenosphere beneath Hawaii) may provide a fixed reference point which can be used to determine absolute motion of the Pacific plate. Return to the image showing the distribution of earthquake epicenters and plate boundaries (the enlarged version). Locate Hawaii and note that the earthquakes are concentrated near the southeastern end of the chain. Ages of volcanism increase to the northwest along the chain. The hot spot is in the asthenosphere and the islands develop in the overlying lithosphere. As the Pacific plate moves to the northwest new lithosphere "sits" on top of the hot spot and a new episode of volcanism is initiated. Follow the chain to the northwest where it becomes the northward trending Emperor seamounts. The "bend" is some 40 million years old. What do you think happened 40 million years ago?

4. Hot spots can occur beneath continents and it is proposed that the Yellowstone area in Wyoming sits on top of a hot spot. If the North American plate is moving to the West, where will the volcanism and thermal affects associated with the hot spot be in a million years?