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A Brief Introduction tch?v=uZp1dNybgfc&edufilter=w EVLZJ6d7xNxQz8CLNMG2g&safe =active.

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2 A Brief Introduction tch?v=uZp1dNybgfc&edufilter=w EVLZJ6d7xNxQz8CLNMG2g&safe =active


4 A Volcano’s Anatomy How Volcanoes Work  Created when a fissure in the earth turns up towards the surface.  The magma moves up the hollow pillar created and out a vent.  Lava build-up from eruptions is what makes volcanoes grow.  The shape and the size of volcanoes are largely dependent on the type of magma within them.

5 Not All Magma Is The Same CompositionSilica Content ViscosityGas ContentTendency to Form Pyroclasts Volcanic Landform Basaltic~50%Least1-2%LeastShield volcanoes, basalt plateaus, cinder cones Andesitic~60%Medium3-4%IntermediateComposite cones Rhyolitic~70%Greatest4-6%GreatestPyroclastic flows, volcanic domes Ejected rock fragments

6 Types of Volcanoes Type of Volcano Description Shield Very shallow slope, typically created from basaltic lava. Often, these come out of the ocean to create islands. (Ex: Hawaii and Iceland) Cinder Cone Formed from ejected lava fragments, steeply sloped. Often the result of a single, long eruption. Usually only erupt once, as the magma pipe often solidifies. Composite Cone Large, made up of alternating layers of lava and ejected volcanic material. Usually have gas-rich and andesitic magma. Have the most explosive eruptions, but the lava only travels a short distance. Composite cones can also produce very dangerous “pyroclastic flows” and “lahars”. The flows are masses of hot gas, glowing ash, and rock fragments rolling down a slope at upwards of 200km/h. Lahars occur when volcanic material mixes with water and creates a dangerous mudflow.


8 Viscosity  “A substance’s resistance to flow.” Ex: Elmer’s Glue is more viscous than water.  Magma from sudden eruptions is typically much less viscous than slowly leaked water, therefor making it flow faster.  Temperature: The hotter something is, the less viscous it is. As lava cools, it hardens and slows down.  The silica content of magma is also directly related to its viscosity. More silica = more viscous.

9 Dissolved Gases  Explosive eruptions can trigger gases trapped in magma to eject molten rock from openings in the surface.  Usually water vapor and CO 2.  As magma gets closer to the surface, the pressure gets reduced, allowing gas to suddenly be released.  Because thinner lava allows these gases to escape more easily, those eruptions are usually much quieter.  Thicker lava traps the gases, creating larger and larger bubbles that increase in pressure until they explosively “pop.”


11 Gases  Pressure can trap dissolved gases in molten rock.  Gas doesn’t make up much of a magma’s weight.  1 – 6%, max  The composition of volcanic gases is important because they have contributed greatly to the gases that make up the atmosphere.  The vast majority of volcanic gas’s composition is water vapor.

12 Pyroclastic Material  Pyroclastic material: the fragments and particles ejected during eruptions  When basaltic lava leaves a volcano (is “extruded”), gas can shoot lava pretty high into the sky.  Some of this material may land near a vent and make cone-shaped structure.  This is pyroclastic material.  Smaller than 64mm: “lapilli”.  Larger: “blocks” when they are hardened. “Bombs” when they are still glowing hot.


14  Calderas – A large depression in a volcano. They usually form from the collapse of a composite or shield volcano.  Necks/Pipes – Pipes are the tube that connects a magma chamber to its vents. If the tube remains standing even after the hill has eroded, it is a neck.  Lava Plateaus – Low-viscosity lava that pours out of fissures on a volcano’s side can create plateaus, as opposed to hill shapes.



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