Presentation on theme: "Volcano Types (39) Volcanoes are either explosive of non explosive."— Presentation transcript:
1 Volcano Types (39) Volcanoes are either explosive of non explosive. Explosives- Mount St. HelensNon-explosive- Kilauea
2 What Controls Eruptions? Two factors1. The amount of water vapor and other gases, which are trapped in the magma.2. Amount of silica in the magmaSilica is a compound of silicon and oxygen.
3 Trapped GasesWater 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
4 Water VaporMagma at some convergent plate boundaries contains water vaporThe trapped water vapor in the magma can cause explosive eruptions.
5 Non-explosive Eruptions Magma with low silica levels called basaltic lava.It is fluid and produces quiet, non-explosive eruptionsAs pahoehoe (pa-HOY-hoy) lava cools, it forms a ropelike structure.Lava flows at a lower temperature, a stiff, slowly moving aa (AH-ah) lava forms.
6 Pillow lavaQuiet eruptions form volcanoes over hot spots such as the Hawaiian volcanoesLavas that flow underwater form pillow lava formations
7 Explosive MagmaSilica-rich, or granitic, magma produces explosive eruptionsMagma is forced upward by denser surrounding rock, comes in contact with the crust, and becomes enriched in silicaSilica-rich granitic magma is thick, and gas gets trapped inside, causing pressure to build up
8 Types of VolcanoesThe three basic types of volcanoes are shield volcanoes, cinder cone volcanoes, and composite volcanoes.
9 Shield Volcanoes Basaltic lava spread out in flat layers. Forms a broad volcano with gently sloping sides.Example- Hawaiian Islands
10 Cinder Cone VolcanoesExplosive 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 steep- sided, loosely packed cinder cone volcano
11 ParicutínOn 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.
12 Composite VolcanoSome 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
13 The __________ the pressure on the gases in magma, the __________ explosive the volcanic eruption. A. greater, lessB. greater, moreC. lower, moreD. pressure doesn’t affect the eruption
14 Which of the following types of magma is most likely to produce violent eruptions? A. basalticB. pahoehoeC. silica-poorD. silica-rich
15 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.