An Island Is Born
OverviewStudents will learn new geological terms such as tectonic plates, hot spot, and shield volcano. Throughout the activity, students will understand the volcanic processes of building new land. They will also learn two types of volcanoes. (Composite, and Shield volcano), and will be able to tell the difference between the two.
Students will be able to:1.Define the vocabulary terms, tectonic plates, hot spots, and shield volcano
2.Identify the differences between the two types of volcano. (shield and composite volcano)
First, we are living on a volcano, which is resting at the moment. Second, our volcano is on the move—it’s traveling towards China. About 1.5 million years ago, our volcano spewed forth enough lava to rise up out of the ocean and become “Tutuila Island.” Actually, just the tip of the volcano is visible to us—most of the volcano is underwater. While the tallest mountain peak --- Matafao on Tutuila is about one half mile high, the mountain extends another two to three miles below the sea surface. It is not much of an exaggeration to call the Samoa islands “active volcanoes.” These islands were formed by volcanism, and the volcanoes are still active, in a geological timeframe of course, and due to some unusual circumstances as described below. The most recent volcanic eruptions were not that long ago. In Samoa, major eruptions occurred in 1905 when lava flows destroyed a village. In the Manu’a Islands, subsurface volcanic eruptions and earthquakes occurred in 1866, causing dense clouds of smoke and pumice to erupt from the ocean’s surface for several months.
The earth’s outer layer, the one we live on, is several miles thick, but that is a thin skin compared to the total size of the earth. This outer layer is made up of many separate sections that seemingly float on top the earth’s molten core and move about in very slow motion. Geologists call these outer sections tectonic plates.You may recall, for example, that the continents of Africa and South America were once joined together when the earth first formed, but the two continents slowly drifted apart to where they are today. The same process applies to the plates under the Pacific Ocean. The plate we’re on is called the pacific plate and it is moving westward (towards China) at a leisurely speed of about three inches per year. At this rate, in one million years we will be fifty miles closer to China. It is not accidental that the Samoa Islands are in a rather straight line. Directly underneath us is what geologists call a hot spot of thermal activity in the earth’s core. It’s a volcano just waiting to happen. When the pressure builds up at the hot spot, molten magma bursts up through the Pacific Plate and forms a volcanic island. The type of volcano that formed our Islands are called shield volcanoes. This type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior’s shield. Then the hot spot calms down for a while, perhaps a million years or so. During this peaceful interval, the Pacific Plate keeps marching onward, so when the hot spot acts up again, it forms a new volcanic island rather than building upon the previous one. In other words, the hot spot stays in one place but the plate keeps moving. The islands generally lie in a straight line that is oriented in the direction the plate is moving. The new islands form on the eastern end of the chain, so the islands become progressively older as you move westward. For that reason, the islands in Western Samoa are about one million years older than the islands in American Samoa. The newest volcanic eruption in our island chain is forming about thirty miles east of Ta’u Island, but it will probably be another few hundred years before this sub-surface volcano, named Vailulu’u, breaks the sea surface (in 2005 it was 1800 feet below the surface and growing).
1. Sand or Soil
2. Empty bottle of water
3. Baking soda
5. Red Kool-Aid
7. Power point presentation
8. Geology video
Introduce Inquiry Question
How do islands form?
Ask: have you heard these terms before? Tectonic Plates, Hot Spot, and Shield volcano? Ask: What do you think these terms mean? Have students watch the power point presentation.
After the presentation, check the students comprehension by asking the questions:
1. What tectonic plate are we on? (Pacific Plate)
3. Are hot spots stationary or moving? (Stationary)
Explain to students that Samoan Islands were formed just like the Hawaiian Islands.
Activity 1: Do-It-Yourself Volcano
1. Place the card board on the floor.
2. Place empty bottle in the middle of cardboard.
3. Place sand or soil around the empty bottle, making sure the entire body of the bottle is covered.
4. Fill the bottle a quarter of the way up with baking soda.
5. Add in red cool- aid or red food color.
6. Pour in vinegar.
Explain to students to observe the eruption, and the slow flow of lava will create new land.
Conclusion with Inquiry Question
How do islands form?
Realizing how our Island formed, this will give us an appreciation of this land we live on and help us to maintain its beauty by picking up trash and not damaging our resources.