EXERCISE PROCEDURE:
The first step of the exercise is to draw in the approximate plate boundaries as indicated by the tectonic activity on the map.
Clues include: (a) The pattern of earthquakes. For example, subduction produces a pattern of deeper and deeper earthquakes as one plate plunges below the other.
(b) The age pattern of volcanic ocean floor rocks suggests the location where new
ocean floor is being created at a midocean ridge.
(c) Volcanic activity may be associated with subduction, spreading centers, or hot spots.
Use the following symbols to indicate the extent of all plate boundaries. Both the map symbols, and a side view of the circumstance they represent, are shown below. Arrows indicate direction of plate movement.
Convergent Boundary Divergent Boundary
After drawing in the plate boundaries using the appropriate symbols on the tectonic map below, answer the questions on the following page. When asked to cite evidence to support your answers, only cite evidence that you can see on this map.
1. (a) How many different plates (not boundaries) are clearly shown on the map? __ _
(b) How many of the plates on the map consist entirely of ocean floor(or ocean floor with islands)?
2. (a) With the number “2” indicate the most likely location on the map or a midocean ridge (such as the Mid-Atlantic Ridge).
(b) What type of plate boundary is this? ______________ _
(c) What evidence shown 011 the map indicates that this type of boundary is present?
3. a) With the number “3” indicate the most likely location on the map of a major volcanic mountain range similar to the Andes in South America.
(b) What type of plate boundary is this? _______________ _
(c) What evidence shown 011 the map indicates that this type of boundary is present?
4. (a) With the number “4” indicate the most likely location on the map of a volcanic island arc.
(b) What type of plate boundary is this? _______________ _
(c) What evidence shown 011 the map indicates that this type of boundary is present?
5. With the number “5” label all plate boundaries where oceanic trenches should be found.
6. a) Assume that only one of the volcanoes on the map is associated with a hot spot. With the number “6” label this volcano.
b) With a 2-centimeter (about I-inch) long arrow extending from this volcano, indicate the direction in which you would expect to find progressively older extinct volcanoes left by the hot spot.
7. In the space below, draw an approximate continuous cross section (“side view”) of the ocean basin from Point “A” to Point “B” (from lower left to upper right). Use the “side view” drawings and Figure 2 for reference, and use arrows to indicate the relative direction of plate motion. If subduction is taking place, clearly show which plate is subducting beneath the other.
1. Complete the chart on the following page:
(a) First, determine the distance between each pair of locations listed on the chart. With a ruler, carefully measure the distance between locations on the map to the nearest millimeter if you use S.I. units and to the nearest l/16 inch if you use English units. If you use English units, convert fractions of inches to decimals to make other calculations easier (for example, I 1/8 :: l. l 25). This figure is the “Measured Distance on Map.” Then multiply this measured distance on the map by 4,200,000 (the denominator of the fractional map scale) to determine the “Actual Distance” in millimeters (or inches).
(b) Next, determine the “Age Difference” in years between each pair of locations. (Be sure to include the correct number of zeros in your figure.)
(c) Finally, divide the “Actual Distance” between locations by the “Age Difference” to estimate the rate of plate movement in millimeters (or inches) per year.
2) Based on the average of your five answers in problem l, what has been the approximate rate of movement of the Pacific Plate in the area of the Hawaiian Islands over the last 5.1 million years?
3) Midway Island, to the northwest of Hawai’i, is also part of the Hawaiian chain and is believed to have been produced by the same hot spot. Midway is about 2430 kilometers (1510 miles) from the Kilauea volcano on Hawai ‘i. Use the average rate of plate movement you calculated in problem 2 to estimate the age of volcanic rocks you would expect to find on Midway Island.
4) The actual age of the volcanic rock on Midway is about 27.7 million years. Suggest a reason why your answer for problem 3 differs noticeably from this.
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