Hot Spots! Original Source: Dr. Leslie Sautter (Dept. of Geology, College of Charleston)

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1 Original Source: Dr. Leslie Sautter (Dept. of Geology, College of Charleston) Grade Level: SC Standards: National Standards: 5 th and 8 th 5 th IIIA1a,b,c; IIIA2a,b 8 th IIIB4f Earth and Space Science Content Standard D Focus Questions How is a chain of volcanoes formed by a hot spot? How can plate rates be determined from chains of volcanoes? Objectives Students will: learn how volcanoes form on a plate that is moving over a hot spot. model the movement of a plate over a hot spot. determine the relationship of volcano age and its distance from the hot spot. relate the modeled volcano formation to the formation of the Hawaiian Islands. Key Words hot spot magma plate seamount volcanic island Materials window screen with frame tube of toothpaste (or a can of shaving cream, or a can of Cheeze-Wiz) masking tape pen that can write on the tape Preparation For this activity, you will need to have all materials ready for each group of students. Also, make copies of the student pages so that they can answer the questions as they do the activity. Time Frame minutes Suggested Learning Environment Collaborative groups of 4 to 6 Relevant pages in Of Sand and Sea Chapter I, The Ocean Planet, pp Teacher Background Information In this activity, students will create a model that shows the development of a chain of volcanic islands formed by a moving plate over a hot spot. Hot spots are sources of rising heat beneath the earth s lithosphere that result in the development of huge magma chambers. Because of magma s lower density, it rises through the overlying denser rock and periodically reaches the surface of the earth. When the magma erupts (becoming lava), a volcano is born. Over millions of years these volcanoes grow from repeated eruptions, adding layer upon layer of newly formed igneous rock (with a basalt composition). Often these hot spots are found beneath the sea floor s oceanic lithosphere and produce underwater volcanoes called seamounts. If a seamount becomes large enough to reach above sea level, we refer to the seamount as a volcanic island. The islands of Hawaii were each formed by the same hot spot. Because we are able to use radiometric techniques to date the volcanic rock produced 1

2 by these hot spots, we have discovered that some volcanic island chains, such as the Hawaiian Island Chain, consist of volcanoes of very different ages. As the Pacific Plate passes over the hot spot, a volcano is born directly above and is active for several million years. With time and movement of the plate, the volcano is carried far enough past the hot spot location to cause its dormancy and extinction. As it moves away from its position above the hot spot, the volcanic island cools and contracts, eventually sinking below the ocean waves. The result is a chain of volcanoes where increasingly older and smaller (from contraction) volcanoes can be found with increasing distance from the hot spot that created them. The Hawaiian Islands range from 0 to 5 million years old! Ancient seamounts that lie beneath the sea surface to the northwest of the Hawaiian Islands are as old as 40 million years. The following activity will demonstrate how a chain of volcanic islands of varying ages can form. Please note that recent evidence suggests that hot spots have, in fact moved through time. However, the amount of hot spot movement is far less than the velocity of the overlying plate. So, for the purpose of illustrating how hot spot formation of seamounts is used to illustrate plate movement, the hot spot in the activity will remain stationary. Procedure Students should follow the steps below, found on the STUDENT PAGES, while taking notes in their science notebook. Information for the teacher is provided in blue italics. In this activity, two students will need to take the job of moving the screen across the top of the toothpaste tube (the hot spot ). A third student will squeeze the toothpaste (as the volcano maker ), and a fourth will be the labeler. The screen your teacher has provided represents a lithosphere plate and will be referred to as a plate. The toothpaste represents a source of rising magma (molten rock), called a hot spot. 1. Select a student in your group and designate him or her as volcano-maker. [If the student is female, you may wish to call her, Pele Goddess of the Volcanoes. If the student is a male, he could be Vulcan God of Lava]. The volcano-maker will hold the toothpaste tube in one place throughout the activity. The toothpaste tube is the hot spot. In this activity, the hot spot will be stationary. 2. Two students will hold the screen, or plate above the hot spot so that the toothpaste tube s nozzle is at one edge or corner of the screen. In this example, the plate is the oceanic lithosphere the volcanoes will form on the seafloor as seamounts. A seamount is a volcano that originates on the seafloor. If it grows long enough so that it extends above the surface of the ocean floor, we refer to it as a volcanic island. Remember that a volcanic island is still a seamount! 3. Note: The screen s motion over the hot spot needs to be very, very slow during the volcano formation. Five volcanoes will be formed as the plate is moved slowly. The path will be in one direction, extending from one edge of the screen to the other. Remind students that 5 volcanic islands have to be made while the screen is moved across the hot spot. Each volcano must be labeled as it is created, and while the screen ( plate ) continues to move. 4. To begin, the volcano-maker should gently squirt a small amount of toothpaste ( magma ) so that it erupts through the plate to simulate the formation of a volcano. Volcanoes tend to erupt episodically; so one or two short squirts will be enough. Name the volcano and label it with the masking tape. 5. Begin to move the plate over the hot spot very, very slowly! After a few centimeters of 2

3 motion, Pele/Vulcan should create a second volcano, while the plate continues to move slowly. This volcano should be named and labeled. 6. Continue to move the plate towards the farthest corner opposite of the starting point and form three more volcanoes (name and label each). When the far corner or edge is reached, there will be five volcanoes, each formed at a different time, with varying distances between each pair of volcanoes. 7. Draw a diagram of your island model, including the names of the volcanic islands. Identify which island is oldest and which is youngest. Note the location of the hot spot. a. Complete the following sentence: As the distance from a hot spot increases the age of a volcanic island (increases, decreases, remains the same). b. Draw a graph that shows the age of a volcanic island on the x-axis and the distance from the hot spot on the y-axis. c. Based on your answer to step 7a, place 5 points on the graph to illustrate the 5 volcanic islands you formed in the activity. Your teacher will provide some examples. d. Label each point with the volcanic island s name. The age of volcanic islands increases with increasing distance from the hot spot. Students should construct a graph like the one illustrated below: oldest (1 st distance from hot spot age of volcanic island volcanic island created) 8. Examine the map of the Hawaiian Islands, provided by your teacher. The largest island, Hawaii has an active volcano, whereas the smaller islands such as Oahu and Kauai have ancient volcanoes that have long been quiet. The oldest rocks of Kauai are more than 5 million years old, and Niihau is even older. a. Where is the hot spot located? b. Based on what you ve learned from your hot spot model, in what direction has the Pacific Plate been moving for the last 5 million years? c. Draw another graph, using the same axes as in step 7b. Place the following six Hawaiian Islands on the graph in the approximate places: Hawaii, Maui, Molokai, Oahu, Kauai, Niihau The hot spot is currently located beneath the island of Hawaii. Since the oldest island listed is Niihau, and it is located to the northwest of the hot spot, the plate must be moving in a northwest direction. Have students model this island arrangement if they do not understand. The graph should look the same as the one in the previous question, but with six dots, labeled in the order shown in step 8c. The island of Hawaii should be at the graph s origin. 9. Compare the activity s model to the depiction of a plate and hot spot provided by your teacher. Describe the similarities and differences between the model and the figure. Summarize your observations and discoveries by answering the questions on the next page. 3

4 Questions (Assessment) 1. Write a short essay (2 to four paragraphs) describing the formation of a chain of volcanic islands produced by a hot spot. See Teacher Background Information for content, along with the activity s stimulated steps. 2. Which of the following graphs best illustrates the relationship between distance from the hot spot and age of the volcanic island? Explain your answer. distance distance distance from from from hot spot hot spot hot spot age of volcanic island age of volcanic island age of volcanic island Thought question: 3. How could the velocity of plate motion (or, the plate rate ) be determined from volcanic islands formed by a hot spot? Since velocity is measured as distance divided by time, the plate rate can be determined as: Plate Rate = distance from hot spot age of volcanic island Source: Dr. Leslie Sautter, Project Oceanica, Dept. of Geology and Environmental Geosciences, College of Charleston, SC. website: oceanica@cofc.edu phone: Funding for the COASTeam Program was provided by the South Carolina Sea Grant Consortium. 4

5 Figure 1 The Hawaiian Islands Figure from: 5

6 Figure 2 Hot spot formation of volcanic island chain. Chains of volcanoes form from the passage of a plate over a hot spot. If the plate is an oceanic plate, as shown below, the volcanoes are referred to as seamounts, and may become volcanic islands, or guyots (see text). The youngest seamount is always directly above the hot spot. Figure from Of Sand and Sea, pg. 15 6