1 / 33

Volcanoes

Volcanoes. MAGMA. All volcanoes are fueled by magma deep beneath Earth’s surface Magma is a mixture of molten rock, suspended mineral grains, and dissolved gases Depending on the composition rocks begin to melt at temperatures between 800°C and 1200°C. Factors affecting magma formation.

lassie
Télécharger la présentation

Volcanoes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Volcanoes

  2. MAGMA • All volcanoes are fueled by magma deep beneath Earth’s surface • Magma is a mixture of molten rock, suspended mineral grains, and dissolved gases • Depending on the composition rocks begin to melt at temperatures between 800°C and 1200°C

  3. Factors affecting magma formation • Temperature • If rocks melt at temperatures found in the asthenosphere, and temperature increases with depth, then why isn’t the entire mantle liquid? • What other factors affect the formation?

  4. Pressure • Pressure increases with depth because of overlying rocks. • As pressure increases, the temperature at which a substance melts also increases • Most rocks in Earth’s lower crust and upper mantle do not melt to form magma even though the temperatures may be hot enough • Greater Pressure = Greater Melting Temperature

  5. Water Content • Water can be found in the pore spaces of some rocks and can be bound into the crystal structure of some minerals • A wet mineral or rock will melt at a lower temperature than the same mineral or rock under dry conditions • Greater water content = lower melting temperature

  6. Magma Composition • Many different factors determine the composition of magma • Viscosity • The internal resistance to flow • Gas Content • Silica Content • Source Material

  7. Magma Types • 3 Different types of magma • Basaltic • Forms when rocks in the upper mantle melt • Low viscosity • Contain small amounts of dissolved gases and silica • Eruptions are relatively quiet

  8. Andesitic • Found along subduction zones • Relatively high silica content • Has an intermediate viscosity • Volcanoes said to have intermediate eruptions

  9. Rhyolitic • Forms when molten material rises and mixes with the overlying silica and water rich continental crust • Highest viscosity • Resistant to flow • Large volume of trapped gas • Very explosive eruptions

  10. Viscosity • Viscosity of magma depends upon temperature and composition • Hotter the magma or lava, the lower the viscosity • Amount of silica in magma or lava also increases viscosity • High in silica = high in viscosity

  11. Intrusive Activity • Magma is less dense than surrounding rocks. • Moves upward and comes into contact with or intrudes the overlying crust • What happens deep in the magma chamber as the magma slowly cools? • As they cool they begin to form intrusive igneous rock bodies ranging in size • These intrusive igneous rock bodies are called plutons

  12. Batholiths & Stocks • Batholiths = largest plutons • Cover at least 100 km2 • Common in the interiors of major mountain chains • Composed primarily of granite • Stocks are irregular shaped and smaller in size than batholiths

  13. Laccoliths • A mushroom-shaped pluton with a round top and flat bottom • Relatively small in comparison to batholiths and stocks

  14. Sills • Sill = a pluton that forms when magma intrudes parallel to layers of rock • Range from only a few centimeters to hundreds of meters in thickness

  15. Dikes • Dike = a pluton that cuts across preexisting rocks • Form when magma invades cracks in surrounding rock bodies

  16. Anatomy of a Volcano • Volcanism produces various features that alter Earth’s landscape

  17. Vent • Opening in the crust through which lava erupts • Over time lava flowing from the vent can accumulate forming a mountain known as a volcano • Crater • A bowl shaped depression, around the vent, at the top of a volcano • Connected to the magma chamber by the vent

  18. Calderas • Craters are usually less than 1km in diameter • Larger depressions = caldera • Up to 50 km in diameter • Can form when volcano summit or side collapses into an empty magma chamber

  19. Types of Volcanoes • Shield • Broad, gently sloping sides • Nearly circular base • Formed when layers of lava accumulate • Non-explosive eruptions • Hawaiian Islands • Ex. Mauna Loa, Kilauea

  20. Cinder-Cone • Formed when material ejected into the air falls back to Earth and piles up around the vent • Steep sides • Small • Magma contains more water and silica = more viscous • Explosive eruptions

  21. Composite • Layers of volcanic fragments alternate with lava • Magma contains large amounts of silica, water, & gas • Much larger than cinder-cones • Violently explosive • Ex. Mount St. Helens

  22. Volcanic Material • Tephra = rock fragments thrown into the air during an eruption • Classified by size • Dust, ash, lapilli, volcanic blocks • Volcanic bombs

  23. Pyroclastic Flow • Clouds of gas, ash, and other tephra • Move at incredible speeds • 200km/h • Temperature can exceed 700°C • 1902 Mount Pelée

  24. Where Do Volcanoes Occur? • 80% occur along convergent boundaries • Subduction zones • Pacific Ring of Fire • 15% occur along divergent boundaries • Rift zones along ocean ridges • 5% occur away from boundaries

  25. Hot Spots • Hot Spots = unusually hot regions of Earth’s mantle • Plumes of material rise toward the surface • Magma melts through the crust to form volcanoes • Creates chains of volcanoes • Provide important information about plate motions • Rate and direction

More Related