GENERAL SCIENCE LABORATORY 1110L Lab Experiment 9B: Tracking the Hawaiian Islands: How Fast Does the Pacific Plate Move? Background You know that the Earth s crustal plates are always moving, but how fast? Each of Earth s plates can move at a different speed and these speeds can change over geological time. But by studying rock formations along boundaries, scientists can figure out how fast each plate has been moving on average over a given time period. Today, students are going to figure out how fast the Pacific Plate is moving using information about the Hawaii. Have you ever visited a hot spot? A scientist named J. Tuzo Wilson once noticed that some volcanoes occur in lines or rows. His theory was that the volcanoes form as small melting areas in the mantle (literally Hot Spots ) and cause magma plumes to break through the crust. As the plate above the hot spot moves, new volcanoes form in a line or chain. The Hawaiian Islands are a classic example of a volcanic island chain formed by the Pacific Plate moving over a hotspot (see picture at left). Do you know of any other examples of hot spots)? Figure 1 Pacific Plate
While visiting Hawaii in the 1960's, Tuzo Wilson, one of the founders of the theory of plate tectonics, noticed some interesting features about ocean islands. On a map of the Pacific basin, he found three linear chains of volcanoes and submarine volcanoes (seamounts). As shown below, these are the (1) Hawaii Islands -Emperor Seamounts; (2) The Pitcairn Island -Tuamotu Group; and (3) the Macdonald Seamount -Austral Group. Notice that the eastern most island or seamount of each chain is volcanically active. Figure 2 Different Groups of Volcanos and remnants of Volcanoes and Seamounts As we can see, although separated by thousands of miles, the three linear chains are parallel to each other. Of the three, the Hawaii-Emperor seamount chain was the most well-known. Wilson reviewed the reports that had been published on these island chains and recorded the age of each island in the Hawaiian chain. An interesting pattern emerged. For each chain, the islands become progressively younger to the southeast. The extreme southeast end of each chain is marked by active volcanoes. Pre Lab Questions Before the groups begin working, each student is to guess how far the Pacific Plate has moved over the average student s lifetime (Assume 20 years). Each students will write their answers down, and a small reward will be given to whichever student in each group guessed the closest.
Figure 3 Location of Earth s Tectonic Plates. Black square represents the area in Figure 6 Wilson proposed that the Hawaiian Islands formed successively over a common source of magma called a Hot Spot The Island of Hawaii is currently located above the hot spot. Figure 4 Present Hawaiian Islands
Hot, solid rock rises to the hot spot from greater depths (see the sketch below). Due to the lower pressure at the shallower depth, the rock begins to melt, forming magma. The magma rises through the Pacific Plate to supply the active volcanoes. The older islands were once located above the stationary hot spot but were carried away as the Pacific Plate drifted to the northwest Figure 5 Present Hawaiian Island Hotspot
Figure 6 The Hawaiian and Emperor Seamount chains. See Figure 2 and black square box on Figure 3 to see location in the Pacific. Radiometric ages determined for basaltic volcanic rocks are shown in parentheses in (in millions of years MY)
Figure 7 Schematic illustration showing the development of a hot spot-related volcanic island chain. The Lithospheric plate has moved away from the observer, over a stationary hot spot(mantle plume) Island #3 was the first to form and did so at the present location of island zero, over the hot spot. Island #3has since been carried, on the Lithospheric plate, to its present location, as was island #1. Hence, island #3, farthest from the hot spot is the oldest and island zero, with active volcanoes, is the youngest. Procedure 1. Complete Table 1 making reference to Figure 6. 2. Record the age of each individual island. 3. Determine the difference in age between each of the labeled islands. Record these differences in the difference in age column. 4. Measure the distance between each of the labeled islands, making reference to the scale on the map (Figure 6). Record these distances in the distance between islands column. 5. Calculate the velocities by dividing the distances between islands by the corresponding differences in age. These results are expressed in km/my. 6. To convert km/my to cm/year, multiply by 100,000 (1 km = 100,000 (cm) and divide by 1,000,000 (1 MY= 1,000,000 years). This is the same as dividing by 10. Record your converted velocities 7. Note and Record directions of movement ( N,NE.E.SE,S,SW,W,or NW) between each of the labeled islands.
Table 1 Island or Seamount Age(MY) Difference in age(my) Distance between islands (km) Velocity (km/my) Velocity(cm/year) Direction of movement Questions 1. Today the Pacific Plate is moving at ~10 cm/year towards the northwest. How does this compare to the velocity of the Pacific Plate over the past 60 MY? Cite times when it has moved at velocities, faster, slower, or equal to toady s velocity. 2. When did the plate shift direction of movement? Cite your supporting observations. 3. The trajectory of plate motion points toward Hokkaido on the northern part of the Japanese Island chain, 6,300 km (3,900 mi) away from the Big Island of Hawaii. A subduction zone offshore of Japan consumes the Pacific plate, which is partly melted to create the volcanoes of Japan. If the "Plate Tectonic Express" operates without change, the Big Island of Hawaii will be headed down the Japanese trench. How long will it take Hawaii to reach Japan? Show your work. Lab Report Format: Your lab report for this experiment should contain the following sections: 1. Title of experiment in center of the first page. Date to the left of the title. Experimenters name with partners name(s) under experimenters name to the right of the title. 2. Objective 3. Apparatus 4. Original Data: Neatly filled out data page. 5. Sample calculations: For this lab an example (ONE) calculation needs to be shown for each of the following: Difference in age between two of the labeled islands. Calculate distance between the same two islands. Calculate the velocity between the same two islands. by dividing the distance between two islands by the corresponding differences in age. These
results are expressed in km/my. Conversion of velocities in km/my to cm/year. All calculations needed to answer Question #3 properly. 6. Results: Make sure the numerical results are properly rounded and have the correct number of significant digits. 7. Conclusions: Address the answers to the three discussion questions below.