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Edit Comment Close Premium member Presentation Transcript VOLCANOES : VOLCANOES Compiled BY: ARVIND TIRKEY CLASS – IX - X Points to Be Covered on Volcanoes : Points to Be Covered on Volcanoes Distribution of volcanoes in relation to plate margins. Causes and effects of volcanoes. Main features of volcanoes and their erruptions. World Famous : World Famous Fujiyama (Japan) Stratovolcano Mt St Helens (USA) Active Stratovolcano Mauna Loa (Hawaii) Shield Volcano Kilimanjaro (Tanzania) Stratovolcano Volcanic Settings : Volcanic Settings Figure 12.24 VOLCANIC DISTRIBUTION : VOLCANIC DISTRIBUTION Characteristics of a VolcanoMagma Intrusions – Rock Formation : Characteristics of a VolcanoMagma Intrusions – Rock Formation Batholith – large irregular discordant intrusions. Stock – smaller irregular discordant intrusions. Dike – a relatively narrow tabular discordant body, often with near-vertical position. Sill – a relatively thin tabular concordant body intruded along bedded planes, often near-horizontal when emplaced, but also may be intruded into tilted beds or the entire package may be tilted by later deformation. Pipe or volcanic neck – circular or tube shaped nearly vertical body which may have been a feeder vent for a volcano. Laccolith – concordant body with essentially flat base and dome shaped upper surface, usually has a feeder pipe below. Lapolith – concordant body with a relatively flat to sagging top and a shallow convex base (spoon shaped), may have a feeder dike or pipe below. Phacolith – a concordant lens-shaped pluton that typically occupies the crest of an anticline or the trough of a syncline. FEATURES OF A VOLCANO : FEATURES OF A VOLCANO A Volcano is an opening in the surface of the Earth from which magma and associated gases and ash erupt. Conical Structure. All Volcanoes have Magma Chamber – huge subterranean caldron of molten rock – less dense – rises buoyantly – under great pressure. The main conduit through which magma moves towards surface is the Central Vent. A Crater sits at the top of a Volcano from where lava, gas, rock fragment and ash eject. Lateral Vents are found on sides of some volcanoes where lava is extruded. Crater Lake formed in the Crater. Also known as Caldera. Volcanic eruptions, especially explosive eruptions, eject fragments of volcanic rocks and lava collectively called Tephra. Ground-hugging and fast moving gas and fragments of rock are pyroclastic flow. Volcanic Hazard : Volcanic Hazard Volcanic Cross - Section : Volcanic Cross - Section CROSS-SECTION OF A VOLCANO : CROSS-SECTION OF A VOLCANO Cross-section through a Stratovolcano 1. Large magma chamber2. Bedrock3. Conduit (pipe)4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15. Ash cloud Gassy Volcanoes –Giving us atmosphere : Gassy Volcanoes –Giving us atmosphere Sangay (Ecuador) Stratovolcano (Active) Kilauea (Hawaiian Islands) Shield Volcano Paricutin (Mexico) Cinder Cone Stromboli (Italy) Stratovolcano Lava Types : Lava Types produced at the constructive plate boundary by the upward movement of magma from the mantle. it is hot. it is fluid, less viscous, flows more rapidly than acidic lava (imagine it as water). flows for quite some distance before solidifying. forms gentle-sloping shield/basic lava volcanoes which erupt quietly. produced when there is subduction at the destructive plate boundary. the subducting oceanic crust melts and the magma produced rises to the surface. it is not as hot as basic lava. it is viscous (sticky), moves slowly (imagine it as glue). cools and solidifies quickly, does not flow far. produces steep-sided volcanoes ie: Mt Fuji in Japan. causes powerful and loud explosions. BASIC ACIDIC Types of Volcano- Frequency of Eruption : Types of Volcano- Frequency of Eruption Active Volcano – Constant emission of lava, dust and smoke. Strong sulphur smell. Dormant Volcano – Has not erupted for hundreds of years. May erupt any time in the future. Extinct Volcano – Has no record of eruption in recorded history. No sign of possible eruption. Fissure Eruptions : Fissure Eruptions Erupt basaltic lava. Low viscosity, moves fast and far. Where are these fissures? The ocean floor in spreading centers. Anywhere on land? Yes, wherever rifting has occurred. Check out the Colombia Plateau. Great thicknesses of basalt lava. Fissure eruptions at Kilauea : Fissure eruptions at Kilauea Kilauea eruption : Kilauea eruption Cinder Cones OR Scoria Cone : Cinder Cones OR Scoria Cone Simplest Types of Volcanoes. Gas-charged lava blown violently into the air – breaks into small fragments – solidify and falls as cinders around vent – to form circular or oval cone. Short, steep slope conical hill. Rock fragments often called cinders or scoria are glassy and contain numerous gas bubbles. Usually bowl-shaped depression at the summit. Paricutin Cinder Cone : Cinder Cone Strato Volcanoes (Composite Cones) : Strato Volcanoes (Composite Cones) Steep sided, symmetrical, tall and Conical Volcano. Composed of many layers of hardened lava, volcanic ash, cinders, blocks and bombs. Example – Mt Fuji (Japan), Mt Cotopaxi (Equador). Lava flows extend laterally. Acidic - Viscous Lava (high in silica), cools and hardens before spreading very far. Alternating lava and pyroclastic layers. A cutaway diagram of a Stratovolcano Mount St. Helens, May 18, 1980 Eruption Strato Volcano OR Composite Volcanoes : Strato Volcano OR Composite Volcanoes Slide 23: Columbia River basalt flow Strato Volcano OR Composite Volcano Shield Volcano : Shield Volcano Large Volcano with shallowly-sloping sides, built entirely fluid basic lava flow. It means broad shield from its resemblance to a warrior’s shield. Form of an inverted shield. Built up slowly by highly fluid lava flow called basalt lava that spread widely over great distance, and then cool as thin, gently dipping sheets. The largest is Mauna Loa on Big Islands of Hawaii. In some eruptions, basaltic lava pours out quietly from long fissure instead of vents and floods the surrounding area with series of lava flow, forming broad plateau. Cutaway image of Shield Volcano Skjaldbreiour – An Icelandic Shield Volcano : Skjaldbreiour – An Icelandic Shield Volcano Spectacular VolcanicFeatures : Spectacular VolcanicFeatures Crater Lake Slide 27: Mt St Helens Slide 28: Sangay Distribution of Volcanoes : Distribution of Volcanoes Convergent plate boundaries Circum-Pacific Ring of Fire Alpine-Himalayan Belt Divergent plate boundaries: Oceanic ridges Mid-Atlantic Ridge Terms used in the study of volcanoes : Terms used in the study of volcanoes Technical Terms Cinder cone Convergent boundary Divergent boundary Fissure eruption Pyroclastics Rift Shield volcano Spreading center Stratovolcano (Composite cone) Non-technical terms Lava Viscosity Student Responsibilities on Volcanoes : Student Responsibilities on Volcanoes What are the products of volcanic eruptions? How do we interrelate magma/lava viscosity, stored gases, violence of an eruption, and distance of transport of the volcanic products? What are fisssure eruptions, shield volcanoes, cinder cones, and strato volcanoes? How do we explain the global distribution of volcanoes? You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.