Purpose of this activity is to demonstrate the action of a shield volcano.
· Half-empty tube of toothpaste
Procedure: Hold the toothpaste tube in your hands. With the cap screwed on tight, push the tube to force the toothpaste toward the capped end. Now use the point of the pencil and make a hole in the tube near the cap. Watch the toothpaste slowly emerge from the hole and flow down the side of the tube. The pressure from the students fingers forces the liquid toothpaste out of the opening.
Why did this happen? Tremendous pressure within the Earth forces liquid rock called magma out of cracks or weak spots in the Earth’s surface. The liquid rock is called magma when it is within the Earth but it is called lava once it reaches the surface. The lava cools and hardens on the surface, forming a mound of rock around the opening. A new layer is added to the mound with each eruption. This layered mount is called a shield volcano. Shield volcanoes are long with gentle slopes, layers of lava that pile up over many years. The crust beneath a Shield volcano has been forced down by their incredible weight. Shield volcanoes in Hawaii are the biggest volcanoes on Earth, formed by lava piling up over hundreds of thousands of years. (Van Cleave, 1991)