Transcript Volcanoes
Volcanoes What is a Volcano? • A volcano is an opening in Earth’s crust through which molten rock, rock fragments and hot gases erupt. How do volcanos erupt? • A volcano may erupt violently or gently. • A violent eruption can cause tremendous destruction even is not much molten rock reaches the surface. • A gentle eruption can pour out rivers of molten lava that flow long distances What is magma? • A major portion of all magma is silica. • Magma also contains gases that expands as the magma rises. • Magma rises toward the Earth’s surface as long as it is less dense then the surround rock. • Once the magma stops rises, it collects in areas called magma chambers. What is magma? • Magma collects in a Magma Chamber before erupting through a volcano. • When magma erupts. It is called lava. • Lava is magma that has reached Earth’s surface. During an eruption • What looks like smoke rising from a volcano is actually a mixture of ash and gases. • Volcanic gases can mix with rock fragments and stay near the ground. – The mixture forms a pyroclastic flow • Which is a dense cloud of superhot gases and rock fragments that races downhill. LAB ACTIVITY What happens when a volcano erupts? • Materials – Empty film canister – Effervescent antacid tablet – Water Everyone must wear their safety googles Procedure • Add water to an empty film canister until it is ¾ filled. • Drop an antacid tablet in the water and put the lid on the canister. • Observe what happens. Answer the following questions: • What happened to the water and to the canister lid? • What caused the changes you observed? • How might the events you observed be similar to the eruption of a volcano? Where do most volcanoes form? • Volcanoes are common along tectonic plate boundaries where oceanic plates sink beneath other plates. • Volcanoes are also common along tectonice boundaries where plates pull apart, allowing magma to rise from the mantle. • The volcanoes around the Pacific Ocean form a belt called the Ring of Fire. The Ring of Fire Subduction zones Name the plate What are the different kinds of volcanoes? Volcanoes do not all look alike. Their shape is based on what type of materials they erupt. There are three main kinds, or shapes, of volcanoes. Classify Volcanoes • Composite • Active • Cinder • Intermittent • Shield • Dormant • Extinct Shield Volcanoes Volcanoes that build up from many slow, steady, flows of hot lava, are called shield volcanoes. This kind of volcano is low and broad with gently sloping sides. They look like a warriors shield. Cinder Cone Volcanoes Cinder cone volcanoes form when solid rock and ash shoot up into the air and fall back around the volcano opening. The cinder cone volcano has steeply sloped sides. Composite Volcanoes Composite volcanoes, erupt with molten lava, solid rock, and ash. The layers pile up much like layers of cake and frosting. The layers form into symmetrical cones, and the slopes are steep. Pictures, Images, and information From: Soames Summerhays/Photo Researchers, Inc. Kraft-Explorer/Photo Researchers Inc. Masao Hayashi-Dung/Photo Researchers Inc. Why Do Volcanoes Blow Their Tops? By Melvin and Gilda Berger www.usgs.gov/education/learnweb/volcano/index.html Label a Volcano Using the labels given find the correct part. Check yourself on the next slide. Parts of a Volcano Where are the Volcanoes? Active Volcanoes of the World 60 50 50 204 70 Indonesia 45 40 20 12 Central America Europe Japan Africa Iceland Italy Ring of Fire 600 South America North America Count the total amount of active volcanoes.