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10.1 – The Nature of Volcanic Eruptions

10.1 – The Nature of Volcanic Eruptions. Do Now. What are the three different types of volcanoes?. Do Now. What are the three different types of volcanoes? Shield Volcano Composite Cone (Stratovolcano) Cinder Cone. Key Words. Explosive Eruption Dissolved Extrude. Vocab Words. Caldera

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10.1 – The Nature of Volcanic Eruptions

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  1. 10.1 – The Nature of Volcanic Eruptions

  2. Do Now What are the three different types of volcanoes?

  3. Do Now What are the three different types of volcanoes? Shield Volcano Composite Cone (Stratovolcano) Cinder Cone

  4. Key Words • Explosive • Eruption • Dissolved • Extrude

  5. Vocab Words • Caldera • Cinder Cone • Composite Cone • Crater • Pyroclastic Material • Shield Volcano • Vent • Viscosity • Volcano

  6. Factors Affecting Eruptions Factors that determine the violence of an eruption. Composition of magma Temperature of magma Amount of dissolved gases in the magma.

  7. Viscosity A substance’s resistance to flow. Ex: Maple Syrup is more viscous than water and flows more slowly. Magma from an explosive eruption may be thousands of times more viscous than magma that is extruded slowly.

  8. Viscosity 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)

  9. Dissolved Gases During explosive eruptions, the gases trapped in magma provide the force to eject molten rock from the vent of the volcano. The vent is the opening in the volcano. These gases are mainly water vapor and carbon dioxide. These same gases expand as they reach the surface. Violence of an eruption is related to how easily gases escape from magma. Viscous magma produces a more violent eruption.

  10. Magma Composition

  11. Volcanic Material • 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 • Pyroclastic Material • Name given to particles produced in volcanic eruptions. • The fragments ejected during eruptions range in size from very fine duct and volcanic ash (less than 2 millimeters) to pieces that weigh several tons.

  12. Pyroclastic Material • Types of pyroclastic materials: • Ash and dust—fine, glassy fragments • Pumice—frothy, air-filled lava • Lapilli—walnut-sized particles • Cinders—pea-sized particles • Particles larger than lapilli • Blocks—hardened lava • Bombs—ejected as hot lava

  13. Pahoehoe Lava Flow

  14. Aa Lava Flow

  15. Types of Volcanoes • The three main volcanic types are shield volcanoes, cinder cones, and composite cones.

  16. Anatomy of Volcanoes • A volcano is a mountain formed of lava and/or pyroclastic material. • A crater is the depression at the summit of a volcano or that which is produced by a meteorite impact. • A conduit, or pipe, carries gas-rich magma to the surface.

  17. Anatomy of Volcanoes

  18. Shield Volcanoes • Shield volcanoes are broad, gently sloping volcanoes built from fluid basaltic lavas.

  19. Cinder Cones • Cinder cones are small volcanoes built primarily of pyroclastic material ejected from a single vent. • Steep slope angle • Rather small in size • Frequently occur in groups

  20. Cinder Cones

  21. Composite Cones • Composite cones are volcanoes composed of both lava flows and pyroclastic material. • Most are adjacent to the Pacific Ocean (e.g., Mt. Rainier). • Large size • Interbedded lavas and pyroclastics • Most violent type of activity

  22. Composite Cones

  23. Other Volcanic Landforms • Calderas • Calderas are large depressions in volcanoes. • Nearly circular • Formed by collapse • Size exceeds one kilometer in diameter • Lava Plateaus • Fluid basaltic lava extruded from crustal fractures called fissures.

  24. Group Activity Fill in the chart on the worksheet. (page 281, Table 1) Also, draw an example of each type of volcano; cinder cone, shield volcano and composite cone.

  25. Videos • http://www.youtube.com/watch?v=xP2dreOI8gI

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