Volcanoes!

1. Volcanoes!

2. What is a volcano? • A volcano is a hole or crack in the Earth’s crust. At a volcano, molten rock from below Earth’s surface can seep through. You might remember that under Earth’s crust, there is a layer of molten rock. This molten rock is a part of the mantle. When a volcano erupts, some of the mantle comes through the crust.

3. What determines the way a volcano erupts? • An eruption can be slow, as when molten rock bubbles up through the crust. Other eruptions can be fast and powerful, spewing ash, hot gases, and rock in all directions. Under Earth’s crust, temperatures are very hot. Rock deep within Earth becomes so hot that is changes from a solid to a liquid.

4. Because liquid rock is less dense than solid rock, it collects in a layer just under the Earth’s hard surface. The melted rock is called magma. When there are cracks and holes in Earth’s crust, the magma can flow through. If the magma is thick, it may flow out slowly. If the magma is thin, it may allow hot gases to escape in an explosion. • “Volcanoes: Mountains of Fire” video 27:00

5. How do scientists classify volcanoes? • Most volcanoes are near the edges of Earth’s tectonic plates. This is because there are more cracks and holes in Earth’s crust in those places. But there are other areas, sometimes called “hot spots” where volcanoes form. The volcanoes that formed the Hawaiian Islands are on one of these hot spots. • “Studying Volcanoes: All in a Day’s Work” eBook Assignment on discoveryeducation.com

6. How do volcanoes change Earth’s surface? • Hawaii is made up of five volcanoes. Kilauea, one of these, is the most active volcano on Earth today. When you think of Hawaii, you might think of tropical birds and beautiful flowers. It might seem strange to think that an area with so many volcanoes is full of life. But that is just one of the many ways volcanoes can surprise you. • Read textbook pages C18-C23. Workbook pages 115, 116.