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Name ________________________________________ Date __________________Lab # __________ Lab Group Members: ________________________________, ________________________________ _________________________________________,______________________________________ The Theory of Plate Tectonics and Hot Spots Hawaii Hotspot (Crustal Plate Movement) Introduction: In 1963, J. Tuzo Wilson, the Canadian geophysicist who discovered transform faults, came up with an ingenious idea that became known as the "hotspot" theory. Wilson noted that in certain locations around the world, such as Hawaii, volcanism has been active for very long periods of time. This could only happen, he reasoned, if relatively small, long-lasting, and exceptionally hot regions -- called hotspots -existed below tectonic plates that would provide localized sources of high heat energy (thermal plumes) to sustain volcanism. Wilson suggested that continuing plate movement eventually carries the volcanic island beyond the hotspot, cutting it off from the magma source, and volcanism ceases. As one island volcano becomes extinct, another develops over the hotspot, and the cycle is repeated. This process of volcano growth and death, over many millions of years, has left a long trail of volcanic islands and seamounts across the Pacific Ocean floor. According to Wilson's hotspot theory, the volcanoes of the Hawaiian chain should get progressively older and become more eroded the farther they travel beyond the hotspot. Origin of the Hawaiian Islands The Hawaiian Islands are the tops of gigantic volcanic mountains formed by countless eruptions of fluid lava over several million years; some tower more than 30,000 feet above the seafloor. These volcanic peaks rising above the ocean surface represent only the tiny, visible part of an immense submarine ridge, the Hawaiian Ridge—Emperor Seamount Chain, composed of more than 80 large volcanoes. This range stretches across the Pacific Ocean floor from the Hawaiian Islands to the Aleutian Trench, Alaska. The length of the Hawaiian Ridge segment alone, between the Island of Hawai'i and Midway Island to the northwest, is about 1,600 miles, roughly the distance from Washington, D.C., to Denver, Colorado. Procedure A: 1. Using Map 1 on this page and the absolute dates of lava in bold black numbers that represent millions of years before the present. Calculate the age difference between the islands and enter the data in the table on page 3. 2. Make distance measurements between the “dots” of each circle using the scale on the diagram. 3. Convert the distance from kilometers to “land” or “real” centimeters (NOT what you measure on the map!) by multiplying the distance in KM by 100,000 (which is the number of cm in 1 km. HINT: This will be a big number! 4. Hawaii contains an active volcano, Mauna Loa, so the lava from it is zero years old (labeled “.01”). The lava on Kauai Island is 5.1 million years old. Thus, according to the hot spot hypothesis, Kauai Island was once an active volcano standing where Hawaii stands today. Map 1 Distance (km) Islands Land Distance (cm) Difference in Age (years) Rate of Movement (cm/year) Hawaii - Maui Maui - Molokai Molokai – Oahu Oahu - Kauai 5. Figure the rate in centimeters per year using the distances from Hawaii to each of the three dated lavas on the map and the following rate equation. Distance between islands (cm) Rate of Movement = Difference in Age (years) Round your answers to the nearest tenth (0.1 cm/year) 6. Now calculate the rate of movement or the average speed of crustal movement and round to the nearest 0.1. Average rate = 7. cm/year In which direction was the crustal plate apparently moving when the Hawaiian Islands were formed? ________________________________________________ Explain how you can tell. 8. According to your data, did the crustal plate always move at the same speed? Explain your answer. ______________________________________________________________________ _____________________________________________________________________________ Part B: Graphing tectonic plate movement over time: A hot spot is a stationary hot area underneath a tectonic plate. Hot magma from Earth;s mantle travels through cracks in the crust at a hot spot and forms a volcano. If the Pacific plate did not move, there would only be one volcano over the hot spot. But as the plates moves, the old volcano moves along with the crust exposing new areas of crust to the hot spot and allowing a new volcano to form. The result is a chain of islands with the youngest island, over the hot spot. This formation gives scientists the unique ability to calculate the rate of movement and determine the direction of movement of tectonic Plates based on the age of each island and the distance between them. DATA: The following are islands that are part of the Hawaiian chain and their age Island Km away from hot spot Age (million years old) 0 Kilauea 0 Kohala 1 0.4 Lanai 20 1.3 0 Kauai 52 5.1 16 Necker 1058 10 9 .3 Brooks Bank 1256 13 .0 Northampton 1841 26 Bank .6 Midway 2432 27 .7 Abbott 3280 38 .7 Yuryaki 3520 43 .4 Koko 3758 48 .1 Suiko Central 4860 64 .7 PROCEDURE: A. Make a graph. On the horizontal X axis you will plot the distance from the hotspot. B. On the vertical Y axis you will plot the age using the data above. The range for the horizontal axis should start at zero and go up by 200’s to 5200. C. Staple your graph to the back of the lab when completed. Make sure your graph has title, labels, units. Interpret your graph: 1) Look at the graph. The slope of the line tells you the rate (or speed) of the plate movement. Based on your graph, has the rate of movement been constant through time? If not explain where/when it was faster? Slower? Explain the reason for your answer by referring to specific ages on the graph. _______________________________________________________________________________________________________________ _______________________________________________________________________________________________________________ _______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ 2) Estimate from your graph: if you find rock that is 55 million years old, how far would it be from the hot spot? Think about it: Hot spots are places where magma is coming up through Earth's crust that are not necessarily located at a plate boundary. As the plates move over the hot spot volcanic islands can form. The block diagram below shows the bedrock age as measured by radioactive dating and the present location of part of the Hawaiian Island chain. These volcanic islands may have formed as the Pacific Plate moved over a mantle hot spot. Use the diagram to the right to answer the following questions. 1. Which island is the youngest? 2. Which island is the oldest? 3. Which compass direction was the Pacific crust moving toward? 4. A new island is already forming off the coast of Hawaii named Loihi. By looking at the diagram to the right, what compass direction (from Hawaii) is Loihi forming? The cross section below shows the direction of movement of an oceanic plate over a mantle hot spot, resulting in the formation of a chain of volcanoes labeled A, B, C, and D. The geologic age of volcano C is shown. 5. What are the most likely geologic ages of volcanoes B and D? a. B is 5 million years old and D is 12 million years old. b. B is 2 million years old and D is 6 million years old. c. B is 9 million years old and D is 9 million years old. d. B is 10 million years old and D is 4 million years old. Base your answer to the question on the world map below and on your knowledge of Earth science. The map shows major earthquakes and volcanic activity occurring from 1996 through 2000. Letter A represents a volcano on a crustal plate boundary. 6. Explain why most major earthquakes are found in specific zones instead of being randomly scattered across Earth’s surface. 7. Identify the source of the magma for the volcanic activity in Hawaii. 8. Identify the type of plate movement responsible for the presence of the volcano at location A.