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Volcanoes

Volcanoes. How and Where do they Form? Analyze how Magma forms as a result of plate motion and interaction Magma and Erupted Materials What different materials erupt from a volcano? Volcanic Landforms What sort of landforms result from volcanic activity. Violent Volcanoes.

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Volcanoes

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  1. Volcanoes • How and Where do they Form? • Analyze how Magma forms as a result of plate motion and interaction • Magma and Erupted Materials • What different materials erupt from a volcano? • Volcanic Landforms • What sort of landforms result from volcanic activity

  2. Violent Volcanoes

  3. Top 5 Volcano Webcams

  4. 10 Most Active Volcanoes

  5. Mt. Etna, Italy

  6. Origin of magma • Magma originates when essentially solid rock, located in the crust and upper mantle- melts • 3 Factors that influence the generation of magma from solid rock: • 1) Heat • 2) Pressure • 3) Volatiles (Fluids/ Gasses)

  7. Role of Heat • Earth’s natural temperature increases with depth (geothermal gradient) is not sufficient to melt rock at the lower crust and upper mantle • Does not melt rock completely

  8. Role of Pressure(In magma formation) Pressure: • Increase in confining pressure causes an increase in melting temperature • So…. More pressure = ??????? • Drop in confining pressure can cause decompression melting • So drop in pressure = ??????? • Occurs when rock ascends

  9. Role of Volatiles Volatiles: • Primarily water • Cause rock to melt at a lower temperature • Play an important role in subducting ocean plates • Seafloor being pulled under continent is easier to melt

  10. Distribution of Volcanos • Ring of Fire- Most volcanoes are located on the margins of the ocean basins • Mid Ocean Ridges- Second group is confined to the deep ocean basins (basaltic lavas) • Hot Spots- Third group includes those found in the interiors of continents(Hawaii)

  11. Locations of some of Earth’s major volcanoes

  12. Plate Motions and Volcanoes • Plate motions provide the mechanism by which mantle rocks melt to form magma • Convergent plate boundaries • Deep-ocean trenches are generated • 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)

  13. Subduction Zone Melting

  14. Magma Formationm @ Divergent Boundaries • Decompression Melting: • Plates are spreading apart, releasing pressure from rock, and allowing magma to rise to surface. • The greatest volume of volcanic rock is produced along the oceanic ridge system

  15. Hot Spots • Hotspots • Activity within a rigid plate • Plumes of hot mantle material rise • Form localized volcanic regions called hot spots • Examples: Hawaiian Islands, Yellowstone

  16. Hawaiin Hot Spot

  17. Why do volcanoes erupt? • Factors that determine the violence of an eruption • Composition of the magma • Temperature of the magma • Dissolved gases in the magma • Viscosity of magma • Viscosity is a measure of a material's resistance to flow

  18. Volcano Lava

  19. Volcanic eruptions • Viscosity of magma • Factors affecting viscosity • Temperature (hotter magmas are less viscous) • Composition (silica content) • High silica – high viscosity (e.g., rhyolitic lava) • Low silica – more fluid (e.g., basaltic lava) • Dissolved gases (volatiles) • Mainly water vapor and carbon dioxide • Gases expand near the surface

  20. Lava Viscosity

  21. Volcanic eruptions • Viscosity of magma • Factors affecting viscosity • Dissolved gases (volatiles) • Provide the force to extrude lava • Violence of an eruption is related to how easily gases escape from magma • Easy escape from fluid magma • Viscous magma produces a more violent eruption

  22. Materials associated with volcanic eruptions • Lava flows • Basaltic lavas are more fluid • Types of lava • Pahoehoe lava (resembles braids in ropes) • Aa lava (rough, jagged blocks) • Gases • One to 5 percent of magma by weight • Mainly water vapor and carbon dioxide

  23. A Pahoehoe lava flow

  24. A typical aa flow

  25. A typical Aa flow

  26. Materials associated with volcanic eruptions • Pyroclastic materials • "Fire fragments" • Types of pyroclastic material • Ash and dust – fine, glassy fragments • Pumice – from "frothy" lava • Lapilli – "walnut" size • Cinders – "pea-sized" • Particles larger than lapilli • Blocks – hardened lava • Bombs – ejected as hot lava

  27. A volcanic bomb Bomb is approximately 10 cm long

  28. Pyroclastic Flows: The Real Threat Bomb is approximately 10 cm long

  29. Lahars: “Cold Lava” Bomb is approximately 10 cm long

  30. Volcanoes – 3 MAIN TYPES • Types of volcanoes • Shield volcano • Broad, slightly domed • Primarily made of basaltic (fluid) lava • Generally large size • e.g., Mauna Loa in Hawaii

  31. A shield volcano

  32. Volcanoes • Types of volcanoes • Cinder cone • Built from ejected lava fragments • Steep slope angle • Rather small size • Frequently occur in groups

  33. Sunset Crater – a cinder cone near Flagstaff, Arizona

  34. Volcanoes • Types of volcanoes • Composite cone (or stratovolcano) • Most are adjacent to the Pacific Ocean (e.g., Mt. Rainier) • Large size • Interbedded lavas and pyroclastics • Most violent type of activity

  35. A composite volcano (stratovolcano)

  36. A size comparison of the three types of volcanoes

  37. Volcanoes • General features • Conduit, or pipe caries gas-rich magma to the surface • Vent, the surface opening (connected to the magma chamber via a pipe) • Crater • Steep-walled depression at the summit • Caldera (a summit depression greater than 1 km diameter)

  38. Mt. St. Helens – a typical composite volcano

  39. Mt. St. Helens following the 1980 eruption

  40. Volcanoes • Types of volcanoes • Composite cone (or stratovolcano) • Often produce nuée ardente • Fiery pyroclastic flow made of hot gases infused with ash • Flows down sides of a volcano at speeds up to 200 km (125 miles) per hour • May produce a lahar - volcanic mudflow

  41. A nueé ardente on Mt. St. Helens

  42. A lahar along the Toutle River near Mt. St. Helens

  43. Mt. St. Helens Eruptions. OMG

  44. Yellowstone Supervolcano

  45. Other volcanic landforms • Calderas • Steep walled depression at the summit • Formed by collapse • Nearly circular • Size exceeds one kilometer in diameter • Fissure eruptions and lava plateaus • Fluid basaltic lava extruded from crustal fractures called fissures • e.g., Columbia Plateau

  46. Crater Lake, Oregon is a good example of a caldera

  47. Crater Lake in Oregon

  48. The Columbia River basalts

  49. 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

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