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Download Volcano Types (39)
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Volcano Types (39) • Volcanoes are either explosive of non explosive. • Ex. • Explosives- Mount St. Helens • Non-explosiveKilauea What Controls Eruptions? • Two factors • 1. The amount of water vapor and other gases, which are trapped in the magma. • 2. Amount of silica in the magma • Silica is a compound of silicon and oxygen. • http://www.bbc.co.uk/science/earth/surface _and_interior/lava#p00h1dn1 • http://www.youtube.com/watch?v=jRfEGvp 6wDU Trapped Gases • Water vapor and carbon dioxide are trapped in magma by the pressure of the surrounding magma and rock. • As magma nears the surface, it is under less pressure, which allows gases to escape, causing non explosive volcanoes. • Gas that builds up to high pressures eventually causes explosive eruptions Water Vapor • Magma at some convergent plate boundaries contains water vapor • The trapped water vapor in the magma can cause explosive eruptions. Non-explosive Eruptions • Magma with low silica levels called basaltic lava. • It is fluid and produces quiet, non-explosive eruptions • As pahoehoe (pa-HOYhoy) lava cools, it forms a ropelike structure. • Lava flows at a lower temperature, a stiff, slowly moving aa (AHah) lava forms. Pillow lava • Quiet eruptions form volcanoes over hot spots such as the Hawaiian volcanoes • Lavas that flow underwater form pillow lava formations • http://www.youtube.co m/watch?v=gn_IW5V sxaw Explosive Magma • Silica-rich, or granitic, magma produces explosive eruptions • Magma is forced upward by denser surrounding rock, comes in contact with the crust, and becomes enriched in silica • Silica-rich granitic magma is thick, and gas gets trapped inside, causing pressure to build up Types of Volcanoes • The three basic types of volcanoes are shield volcanoes, cinder cone volcanoes, and composite volcanoes. Shield Volcanoes • Basaltic lava spread out in flat layers. • Forms a broad volcano with gently sloping sides. • Example- Hawaiian Islands Cinder Cone Volcanoes • Explosive eruptions throw lava and rock high into the air. • Bits of rock or solidified lava dropped from the air are called tephra. • Tephra varies in size from volcanic ash, to cinders, to larger rocks called bombs and blocks. • When tephra falls to the ground, it forms a steepsided, loosely packed cinder cone volcano Paricutín • On February 20, 1943, a Mexican farmer noticed that a hole in his cornfield that had been therefore as long as he could remember was giving off smoke. • Throughout the night, hot glowing cinders were thrown high into the air. • In just a few days, a cinder cone several hundred meters high covered his cornfield. Composite Volcano • Some volcanic eruptions can vary between quiet and violent. • An explosive period can release gas and ash, forming a tephra layer. • Quieter period, erupting lava over the top of the tephra layer The __________ the pressure on the gases in magma, the __________ explosive the volcanic eruption. • A. greater, less • B. greater, more • C. lower, more • D. pressure doesn’t affect the eruption • Which of the following types of magma is most likely to produce violent eruptions? • A. basaltic • B. pahoehoe • C. silica-poor • D. silica-rich • 3. Explain the difference between an explosive and non-explosive eruptions. • Explosive volcanoes have magma which is silica rich, with large amounts of trapped gases. Magma is thick. • Non-explosive volcanoes have magma which is silica poor, with minimal amounts of trapped gases. Magma is fluid and liquid and spreads out.