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Chapter 6- Volcanoes

Chapter 6- Volcanoes. Which statement concerning volcanoes is accurate?. All volcanoes erupt explosively. Lava is the most deadly thing about volcanoes. Volcanic eruptions can influence the climate of Earth. Volcanoes occur in random locations on the surface of Earth. Volcanoes.

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Chapter 6- Volcanoes

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  1. Chapter 6- Volcanoes

  2. Which statement concerning volcanoes is accurate? • All volcanoes erupt explosively. • Lava is the most deadly thing about volcanoes. • Volcanic eruptions can influence the climate of Earth. • Volcanoes occur in random locations on the surface of Earth.

  3. Volcanoes expulsion of molten rock (Lava), gases and water vapor onto the surface of the Earth. sometimes violently, sometimes not • - 1500 active volcanoes > Active = erupted in recorded history - e.g. Mauna Loa and Kilauea (Hawaii) - Mt. St. Helens (Washington) - Mt. Pinatubo (Philippines) - Mt. Fujiyama (Japan) - Mont Serrat (Caribbean) Mt. Fujiyama, Japan

  4. Dormant Extinct Volcanoes vs Dormant volcanoes Dormant volcanoes • • - have not erupted recently, but may do so again. - have not erupted recently, but may do > Mt. Vesuvius (Italy) > Mt. Vesuvius (Italy) Extinct volcanoes • • Extinct or inactive volcanoes - have not recently erupted - nor do they give indications of erupting in the future. Thousands of these > > types ofvolcanoes exist. Mt. Kilamanjaro (Tanzania,Africa)

  5. Types of Volcanoes

  6. A small shield volcano in Iceland

  7. What materials are not commonly associated with volcanic eruptions? • Lava • Steam • Gasses • All of the above are associated with volcanic eruptions

  8. Discussion: Why do some volcanoes erupt explosively, whereas others erupt in a more subdued fashion that is not explosive? Water in magma more water = more explosive Magma composition high silica content = high viscosity (flow resistance) high viscosity = more explosive Magma Temperature cooler = higher viscosity (see above) Gas content more gas = more explosive All factors are related to tectonic location

  9. a.k.a.- stratovolcanoes • - interbedded pyroclastics and lavas. - typically andesitic to rhyolitic lava > intermediate to felsic magma composition - Found on continents and island arcs > mostly associated with convergent plate boundaries (subductive) > examples of composite Mt. St. Helens, Mt. Vesuvius, Mt.Pinatubo, Mt. Fujiyama, Mt. Kilamanjaro., Mt. Rainier (photo) Composite Volcanoes

  10. Stratovolcano formation

  11. Composite or Stratovolcanoes Mayon volcano, Philippines, is a Mayon volcano, Philippines, is a View of Mount St. Helens, View of Mount St. Helens, nearly symmetrical composite nearly symmetrical composite Washington in 1978. Washington in 1978. volcano. volcano.

  12. Cinder Cones Primarily cinder-sized (0.25-1.0 mm) material. but may have other sizes too. Cinders fall to Earth and collect around the vent. have steep slopes up to 33 degrees smaller than shield volcanoes, usually less than 400 m tall Form on the flanks of larger volcanoes.

  13. Cinders and volcanic ash

  14. Lava Types Pahoehoe lava (smooth & ropey) in Aa lava (rough and blocky) also Pahoehoe lava (smooth & ropey) in Aa lava (rough and blocky) also Hawaii. in Hawaii. Hawaii. in Hawaii. Lower viscosity lava Higher viscosity lava

  15. Pillow Lavas These bulbous masses of pillow These bulbous masses of pillow lava formed when lava erupted & lava formed when lava erupted & cooled under water. cooled under water. 1 meter 1 meter

  16. Lava Fountain Lava Fountain

  17. It is possible to drive faster than lava flows to escape it? • True • False

  18. It is possible to outrun a pyroclastic flow in a car. • True • False

  19. Pyroclastic Ash Flow ' aka Nuee Ardentes aka Nuee Ardentes Pyroclastic ash- lava blown up into the air • smaller stuff is ash, larger stuff are called "bombs" Pyroclastic Ash Flow • extremely fast (100's m/sec) • extremely hot - sometimes glowing redhot • extremely lethal - many deaths associated with volcanic eruptions are related to these events e.g., Pompeii and Herculanum >

  20. Ash plume from a stratovolcano eruption

  21. Pyroclastic flow , Nuee Ardente

  22. , Lahars & Nuee Ardentes • Lahars are mud flows that often occur after eruptions. • Nuée ardentes are mobile dense clouds of incandescent ash that can move downhill at , speeds up to 100 km/hr. Mt Pelee destroyed St. Pierre on the island of Martinique, West Indies in 1902

  23. The effects of explosive volcanic activity Casts of people from Pompeii, killed by ash from Mt. Vesuvius, Italy

  24. Gases and Magma • Volcanic gases - water vapor - carbon dioxide - nitrogen - sulfur oxides - hydrogen sulfide - chlorine • Felsic magmas - highly viscous : Si-rich - inhibits the expansion of gases - pressure builds up - explosive eruptions, like Mt. St. Helens. • Mafic magmas - lower viscosity - lower gas pressure - erupt rather quietly, like Hawaiian Volcanoes.

  25. Lake Nyos, a volcanic lake in Cameroon, Africa CO2 emitted from the acidic lake killed 1700 villagers near the lake in 1986

  26. Mt. St. Helens- May 18, 1980

  27. Yellowstone Caldera

  28. Bathymetry map of Crater lake, Oregon

  29. Volcanoes are randomly distributed around the world with no discernable pattern? • True • False

  30. Distribution of volcanoes is not random • related to plate tectonics • commonly found along plate boundaries

  31. Effects of Volcanoes and their activity • builds up mountains and new land or destroys old (geosphere) - • kills many living things (biosphere) - • ejects ash and gases into the air Changing weather and climate patterns for several • months to a year (atmosphere) - Causes changes in drainage patterns, and pollutes • many water sources (hydrosphere) - Ash blocks incoming sunlight from space (exosphere)

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