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Map of Volcanoes around the WORLD! Volcano Discovery • http://webcams.volcanodiscovery.com/Kilau ea • This site allows you to look at what is currently happening around the world with volcanoes and earthquakes! What is the difference between magma and lava? • REVIEW: What is the type of rock that forms when magma cools and hardens? Magma is below the Earth and forms intrusive igneous rock • What type of rocks forms when lava cools and hardens? Lava is what comes out of the volcano and forms extrusive igneous rock • THEY ARE BOTH TYPES OF IGNEOUS ROCK! What’s the difference?! –Think location… How a volcano erupts is based on viscosity. 1. What is viscosity? • Viscosity is how resistant a substance is to flowing. For example, honey is more viscous than water. • Magma that contains more silica will be more viscous, magma that contains less silica will be less viscous. • Magma that is very viscous will explode, magma that is less viscous will flow. • Lava that is hotter will be less viscous (like if you heat up honey) and will flow more. • Lava contains dissolved gases, and if the lava is very viscous, those bubbles cannot expand. Instead, the bubbles will explode upwards. Viscosi – what?! • If the Shield volcano has faster flowing lava that creates new land, does it have a high viscosity or low viscosity? • If the Composite Cone has a slower flowing lava that explodes due to the high content of silica, does it have a high viscosity or low viscosity? HOT SPOTS! • Volcanic regions that are fed by the mantle below and are much hotter than the mantle in other parts of the world • Occur at divergent boundaries Convergent Boundaries: Subduction • Convergent boundaries form volcanic island arcs. These form over subduction zones • The plate that is subducted releases water into the overriding plate and causes some rock to melt • ex: Alaska volcanoes or Mt. St. Helens – cinder cones • http://www.youtube.com/watch?v=9 CxhOpk3J7Y Divergent BoundariesHot Spots • Divergent boundaries form hot spots – ex: Hawaiian islands and the RING OF FIRE – shield volcanoes, composite cones, etc. Volcanoes also eject pyroclastic materials, • These particles can be as small as ash or as large as boulders. There are 3 main types of volcanoes, but they all have this general form: Shield Volcanoes • Made of very fluid lava that spreads really far and hardened. • Broad shape • Lots of island volcanoes (for example, Hawaii) • Eruptions are not very violent • Hot spot or subduction? Cinder cone volcanoes • Ejects lots of cinders (chunks of pyroclastic material) that accumulate at the bottom. • Steep sides • Short lifespans (usually only erupt once). • Usually pretty small • Hot spot or subduction? Composite cone volcanoes • Huge! • Produce both lava and pyroclastic material that can reach up to 120 mph! • Usually found in the Ring of Fire, which is a zone of volcanoes that circles the Pacific Ocean. • Can sometimes form lahars, which are mudflows that are made when lava mixes with water and soil. • Hot spot or subduction? Draw! Calderas • Calderas are volcanic depressions that are created when the magma chamber is drained and the volcano collapses in on itself. Instead of looking like a mountain, it looks like a valley. Volcanic necks • Volcanic necks are formed when a volcano has been weathered down so that only the magma conduit (pipe) is left. Lava plateaus are made from very lowviscosity lava flowing out of a fissure (crack) in the ground. The lava spreads really far and creates a flat landform.