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Volcanoes and Other Igneous Activity

Volcanoes and Other Igneous Activity. Volcanoes: Content Standards Addressed. Origin of magma. Magma originates when essentially solid rock, located in the crust and upper mantle, melts. How Magma Rises. Where do volcanoes form?. Volcanoes form at:

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Volcanoes and Other Igneous Activity

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  1. Volcanoes andOther Igneous Activity

  2. Volcanoes: Content Standards Addressed

  3. Origin of magma • Magma originates when essentially solid rock, located in the crust and upper mantle, melts

  4. How Magma Rises

  5. Where do volcanoes form? • Volcanoes form at: • Hot Spots (10% of all volcanic activity)

  6. Where do volcanoes form? • Volcanoes form at: • Hot Spots (10%) • Spreading Centers (80% of all volcanic activity)

  7. Where do volcanoes form? • Volcanoes form at: • Hot Spots (10%) • Spreading Centers (80%) • Convergent Plate Boundaries (10% of all volcanic activity) • Ocean–Continental • Ocean – Ocean

  8. Plate tectonics and igneous activity • Intraplate igneous activity • Activity within a rigid plate • Plumes of hot mantle material rise • Form localized volcanic regions called hot spots • the Hawaiian Islands & the Columbia River Plateau

  9. Plate tectonics and igneous activity • Divergent plate boundaries • Produces the greatest volume of volcanic rock • Lithosphere pulls apart • Less pressure on underlying rocks • Partial melting occurs • Large quantities of fluid basaltic magma are produced

  10. Plate tectonics and igneous activity • Convergent plate boundaries • Descending plate partially melts & magma slowly rises upward • Rising magma can form • Volcanic island arcs in an ocean (Aleutian Islands) • Continental volcanic arcs (Andes Mountains)

  11. Tectonic Settings and Volcanic Activity

  12. Plate Boundary Features

  13. Volcanic Eruptions • Factors that determine the violence of an eruption • Temperature of the magma • Composition of the magma • Dissolved gases in the magma • The above three factors actually control the viscosity of a given magma which in turn controls the nature of an eruption

  14. increasing increasing increasing Viscosity, Temperature and Water Content of Magmas

  15. Why more volcanic activity at spreading centers? Low SiO2 content High temperature Low pressure as plates pull apart Fluid basaltic lavas generally produce quiet eruptions Why less volcanic activity at subduction zones? High SiO2 content Lower temperatures Higher pressures Highly viscous lavas produce more explosive eruptions Plate-Tectonic Setting of Volcanoes Revisited

  16. Volcanic Explosivity Index Source: http://volcano.und.edu/vwdocs/eruption_scale.html

  17. Volcano: Any landform that releases lava, gas, or ashes or has done so in the past • Refers to both the VENT and the CONE • Many shapes and sizes due to magma chemistry and origin

  18. Volcano Types

  19. Volcanoes can be classified into 6 major types • Volcanoes can be classified into 6 major types Based on their size, shape, and origin

  20. Features Of The Two General Categories Of Volcanoes Central Vent Volcanoes Large-scale Volcanic Terrains no central vent network of source material generally massive • central vent • summit crater • flank eruptions • fissure eruptions

  21. Comparison Of The Six Types Of Volcanoes

  22. Shield volcano • Low silica, low gas magma originates in the mantle = fluid, basaltic lava • Broad, gentle slopes. • Phreatomagmatic eruptions occur when lava contacts water.

  23. Mauna Loa SHIELD VOLCANOES ARE A TYPE OF CENTRAL VENT VOLCANO.

  24. Cinder Cones • high lava fountains on the vents of shield volcanoes. • Composed of pyroclastic debris. • Cinders formed by high gas content.

  25. Sunset Crater, Flagstaff, Arizona

  26. Mt. Fuji Aniakchak Caldera Stratovolcanoes And Rhyolite Caldera Complexes Are Central Vent Volcanoes.

  27. Composite cone or stratovolcano • Alternating andesitic lava flows and layers of explosively ejected pyroclastics. • Intermediate magma = viscous lava that is difficult to erupt. • Explosive eruptions due to buildup of gases. • Often produce nuée ardente • May produce a lahar - volcanic mudflow

  28. Mt. St. Helens

  29. New Dome Vent 1980-1986 Dome Rock Glacier Mt. St. Helens http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16721

  30. Mt. St. Helens, October 1, 2004 http://www.nasa.gov/vision/earth/lookingatearth/mshelenslidar.html

  31. Eruptions in the Cascades Ranges

  32. Calderas • High-silica, high-gas magmas. • Massive explosions (most explosive of all types). • Collapse, producing an “inverse volcano”, or Caldera (Spanish for cauldron).

  33. Calderas • Famous (or infamous) collapsed calderas: • Long Valley, California (Mammoth) • Crater Lake (Mount Mazama), Oregon • Yellowstone, Wyoming • Krakatau, Indonesia, 1883 • Santorini and the Lost Continent of Atlantis

  34. How Calderas Form

  35. Large-scale volcanic terrains lack a central vent

  36. Monogenetic Fields • Poorly understood. • Multiple maar vents and cinder cones. • Erupt at different times. • Grow laterally. • Usually a single magma source San Francisco Volcanic Field

  37. Monogenetic Fields • Large Igneous Provinces • Fed by massive mantle plumes • Caused by flood basalts • Discharge over time through longfissures (cracks). • Create large plateaus. Columbia River Basalts

  38. The Columbia River basalts

  39. Monogenetic Fields • Mid-ocean Ridges • develop at Spreading Centers • Basaltic flow creates global network of interconnected ridges submarine volcanism

  40. Other volcanic landforms • Lava Domes • Bulbous mass of congealed lava • Most are associated with explosive eruptions of gas-rich magma • One is currently developing in Mt. St. Helens

  41. Other volcanic landforms • Volcanic pipes and necks • Pipes are short conduits that connect a magma chamber to the surface • Volcanic necks (e.g., Ship Rock, New Mexico) are resistant vents left standing after erosion has removed the volcanic cone

  42. Formation of a volcanic neck

  43. Damage is caused by: Volcanic Hazards Threaten Human Communities Lava flows Pyroclastic flows. Lahars(mudflows). Ash falls. Volcanic bombs. Massive lethal, violent explosions. Earthquakes. Landslides. Open cracks and chasms. Phreatomagmatic eruptions. Climate change.

  44. Lava flows Molten rock that has flowed out onto the Earth’s surface

  45. Pahoehoe lava (braids or ropes)

  46. Aa lava (rough, jagged)

  47. Pillow basalts

  48. Gases • One to 5 percent of magma by weight • Mainly water vapor and carbon dioxide

  49. Pyroclastic materials Ash and dust – fine, glassy fragments Pumice – from "frothy" lava Cinders – "pea-sized" Lapilli – "walnut" size Particles larger than lapilli Blocks Bombs weblink

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