Download ppt - Chapt10.1 volcanoes

  • 1. Chapter 10 section 1 volcanoes and other igneous activity

2. viscosity Is a substances resistance to flow Temperature on viscosity easy to see Mobility of lave strongly affected by temperature Chemical composition of magma has more important affect on the type of eruption The more silica in magma the greater it is viscosity High silica means slowerflow Lower silica faster flow 3. Dissolved gasses During eruption ,the gasses trapped in magma provide the force to eject molted rock Vent-an opening to the surface. Mostly water vapor and carbon dioxide Fluid basaltic magma allows expanding gases to bubble upward and escape easily Most are quite 4. Lava flow o Most lava is very fluid because of the low amount of silica o Flow rate at 10 to 300 meters per hour o Silica rich lava is slower o When basaltic lava harden it makes a smooth skin that wrinkles known as Pahoehoe o Aa is another form of basaltic lava o Rough jagged blocks o With dangerously sharp edges 5. Pyroclastic materials When lava is extruded Some ejected lava may land near the vent and forma cone shape Wind will carry small partials a long way The fragment ejected during eruption range in size from very fine dust and volcanic dust to pieces that weigh several tons 6. Type of volcano Theyre three main volcanic type Shield volcanoes Cinder cones Composite cones Anatomy of a volcano Activity often begins when a fissure or develops in the crust 7. Shield volcanoes Are produced by the accumulation of fluid basaltic lavas Shape of broad slightly domed Most have grown from the deep of the ocean Including Hawaiian island and Iceland 8. Cinder cones Ejects lava which hardens in the air Range in size from fine ash to bombs but mostly lapilli Produce gas rich basaltic magma Come in simple shapes Shape determined by steep- sided slope Last only a couple of weeks because of short life span cinder cones are small between 30 to 300 miters 9. Composite cones Most beautiful but also most dangerous Also known as stratovolcanoes Located in relatively narrow zones Pacific ocean (ring of fire) Cascade range, mount. St.Helen, mount. Rainier, andmount. garibaldi Most activity are located in the curved belts of volcano island 10. Lava plateaus Greatest volume of volcano excrete from fissures Columbia plateau was formed this way Numerous fissure erupted their Some go up to50 miters thick but some only 1.6 miters thick