December 18, 2012 Q-2 Pg. Daily Goal: We will explain why volcanoes erupt and how volcanoes are different from mountains. Homework: Revise your test! Science Starter: 1. How are island chains formed? 2. List one positive and one negative effect of volcanoes. Mountains and Volcanoes What’s the difference? • Mountains Remember when we made mountains with graham crackers? • Which type of boundary made mountains? Mt. Everest is the tallest mountain (above water) in the world. • Mt. Everest was once the floor of a shallow sea. If you were to climb Mt. Everest, you would be standing on rocks containing the remains of ocean animals. • How can rocks from the sea floor be on top of a mountain on a continent? Mountain ranges happen at convergent plate boundaries. • When two plate boundaries collide, the plates push together. Plates can be oceanic or continental. The land has nowhere to go but up. Volcanoes can also happen at plate boundaries. • A volcano is an opening in Earth’s crust which molten rock, rock fragments and gasses escape. How Magma Forms at a Divergent Boundary •Mantle material rises to fill the space opened by separating tectonic plates. As the pressure decreases, the mantle begins to melt and rise up. •Because magma is less dense than the surrounding rock, it rises toward the surface, where it forms new crust on the ocean floor. How Magma Forms at a Convergent Boundary •As the oceanic plate moves downward, some of the rock melts and forms magma. •When magma is less dense than the surrounding rock, it rises towards the surface. Mountains don’t erupt. Volcanoes do. Why? • The mantle holds a lot of gasses. • Remember what happens when gas gets hot? – Does it spread out (become less dense) or pack together (become denser)? • Do less dense things rise or sink? ***Write this down!*** • When the gas rises, it pushes against the crust, and creates a lot of pressure. This pressure creates cracks. The cracks open up space for the magma to get through. In your notebook, • Explain what we did for the demo. • Explain how the demo is like a volcano. – Be sure to include the words: pressure, gas, expand, dense, erupt • Draw a diagram of the demo. – Label what is happening. (Include the direction.) • Draw a diagram of a volcano. – Label what is happening. (Include the direction.) Ring of What is the ring of fire? Write down what you think the 3 key points are from the text we just read.