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THE HAWAIIAN ISLANDS & CONTINENTAL DRIFT Name: _________________________ Background As you well know, the Hawaiian islands are located far away, near the middle of the Pacific Ocean, 4,000 km (2,500 miles) from the nearest continent. The Hawaiin islands are rather young landmasses and did not originate during the breakup of Pangea into Gondwana and Laurasia, or subsequent breakups. Rather, the Hawaiin islands are volcanic in origin, and as you have learned, the age of volcanic ash or rock can be determined using radioactive dating methods. More specifically, this metamorphic rock contains radioactive potassium isotopes that decay into the more stable argon gas. In the following activity, you will you use your knowledge of radioactive dating to learn about the rate of continental drift while developing a deeper understanding of the tectonic activity that has lead to the development of the Hawaiian islands. This activity will also prepare you for further activities where you will come to a deeper understanding of speciation and the adaptive radiation that has occurred on these islands. Procedure & Questions Surf to http://pubs.usgs.gov/publications/text/hotspots.html. 1. Describe J. Tuzo Wilson’s “hotspot” theory. What prediction does it make about the Hawaiian islands? 2. How are ancestral Hawaiian myths consistent with this theory of the origin of the islands? Use the following graph relating the percent of parent or original potassium to its age, to determine the age of the volcanic rock associated with each of the main Hawaiian islands. Record your answers in the table provided. Hawaiin Island Main Volcano Parent Material (K) 118.8 Daughter Material (Ar) 1.2 Hawaii Mauna Kea Maui 117.6 2.4 Oahu Haleakal (Red Hill) Waianae 114.0 6.0 Kauai Kauai 111.6 8.4 Nihoa* Nihoa 109.2 10.8 Necker* Necker 106.8 13.2 % of Parent Material Age (MYA) *Are not currently Hawaiian island but mountains below sea level. 3. Is this data consistent with the Wilson’s hotspot theory? Explain. 4. Based on your knowledge of the age of the islands, in which direction is the plate moving through which the hotspot is acting? Explain. 5. Is there a pattern to the height of the volcanoes on the Hawaiian islands as reported on the map on the following page? Why would this pattern exist based on your knowledge of the age of the islands? If we now assume that the hotspot theory is correct, a few easy steps will allow you to determine the rate of movement of the pacific plate. 6. Assuming that the hotspot that is currently under Mauna Kea on Hawaii has not moved, use the scale on the map above to determine how far each islands midpoint has traveled from the hotspot (Mauna Kea). Fill in the age of each island again too. Hawaiin Island Hawaii Maui Main Volcano Mauna Kea Distance (km) - Oahu Haleakala (Red Hill) Waianae Kauai Kauai Nihoa* Nihoa 775 km Necker* Necker 1050 km Age (Millions of Years) 7. Using the distance from Mauna Kea to Necker and the age of Necker, calculate the average speed at which the plate on which the Hawaiian islands exist has been moving in centimeters per year (hint: convert km to cm, and millions of year to years before calculating). Show your work. Does this rate seem slow? 8. Using the data from the previous table, construct a graph (x-axis = Distance in km, yaxis = Age in millions of years). Label your data points with the island names. 9. Based on the graph, does it appear that the plate movement has been consistent over the past 10 million years? Explain. 10. What does the pacific ridge, in the picture to the right, suggest about this movement? Post Homework Discussion Question 1. Assuming that the islands of Maui and Kauai were the exact same height as Hawaii is today, calculate how many millimeters of height have been lost on both islands. Then, using those answers and your knowledge of the time that has elapsed since these islands have formed, and how many millimeters of height has been lost per year on both islands. 2. Necker island is currently 100 m above sea level, and is estimated to have been as high as 1000 m in the past. Using this information and the age of the Necker Island, alculate how many millimeter of height has been lost per year. 3.