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The Stages of An Island Arc |
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Background: The oldest rocks in the Aleutian Mountain Range are basalt rocks. They were formed through magma flows from an ocean trench south of the equator 300 million years ago, forming an island arc similar in its geologic history to the island arc further to the west known as the Hawaiian Islands. According to the theory of plate tectonics, the Earth's surface is made up of a patchwork of about a dozen large plates that move relative to one another at speeds from less than one centimeter to about ten centimeters per year about the speed at which fingernails grow. Averaging a thickness of about 80 kilometers, these rigid plates are spreading apart, sliding past each other, or colliding with each other in slow motion on top of Earth's hot, pliable interior. Volcanoes tend to form where plates collide or spread apart, but they can also grow in the middle of a plate, as for example the Hawaiian volcanoes. Magma is molten rock below the surface of the Earth, rising up in volcanic vents. But, after it erupts from a volcano, it is called lava. Originating many tens of miles underneath the ground, the ascending magma commonly contains some crystals, fragments of surrounding (unmelted) rocks, and dissolved gases. Primarily, though, it is a liquid composed principally of oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, potassium, titanium, and manganese. Upon cooling and until solidification is complete, the liquid magma may precipitate crystals of various minerals to form an igneous or magmatic rock.
Resources/Materials/Supplies Video Segment - Program #1 and #2 Internet access Flour and Salt Relief Recipe or Paper Mache Recipe and ingredients
Description: In this activity students will: Read information on the development of the Hawaiian Islands in the Pacific Ocean found on the Web. In small groups create scale models of the stages of development of an island arc such as the Hawaiian Islands. Students will label their model and write a brief explanation of the stage of development their model shows. Their explanations should describe the volcanic and other geologic activities that take place at that stage.
Management Hints and Tips Work with the class to determine what material will be used to create the models. Enough clay for everyone would probably be expensive; Flour and Salt is not as messy as Paper Mache and will dry quicker. Paper Mache is messy and takes a while to dry but is long lasting. Each group will model one stage of the development of an island arc, label the important features of their assigned stage and explain what volcanic activity is taking place. Work with the class as a whole to determine:
Be sure students have plenty of the ingredients and equipment needed to create their models (See Relief Recipes.) They will also need places in the classroom to work on their model that are protected from spills and other student's interest. Allow students to read the information at the attached Hot Links before dividing them into groups. After they have built their models, students will need time to allow the material to dry before they can paint. Be sure all models are appropriately labeled so that a viewer will understand what volcanic activity a model represents and what materials, such as pillow lava or coral reefs, are shown. |