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VOLCANOES

VOLCANOES. CHAPTER 7. 7.1 VOLCANOES AND PLATE TECTONICS. Section Objectives: Describe the formation and movement of magma Define volcanism List three locations where volcanism occurs. I. VOLCANISM.

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VOLCANOES

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  1. VOLCANOES CHAPTER 7

  2. 7.1 VOLCANOES AND PLATE TECTONICS • Section Objectives: • Describe the formation and movement of magma • Define volcanism • List three locations where volcanism occurs

  3. I. VOLCANISM • Volcanism is any activity that includes the movement of magma toward or onto the surface of the earth. • Asthenosphere is very hot but stays mostly solid because of the great pressure of the surrounding rock. • Magma forms where decreased pressure allows the rock to melt • Lower density of magma compared to the surrounding rock and allows it to rise toward the surface.

  4. I. VOLCANISM • Lava: Magma that reaches Earth’s surface • Vent: The opening through which the molten rock flows onto the surface • Volcano: The structure that is formed by the vent and volcanic material that builds up on Earth’s surface around the vent

  5. volcano lava vent cone

  6. II. MAJOR VOLCANIC ZONES Three major locations where volcanism occurs: • Subduction Zone • Mid-ocean Ridge 3. Hot Spot

  7. Subduction Zone

  8. Mid Ocean Ridge

  9. Hot Spot

  10. VOLCANIC ERUPTIONS Section Objectives: • Summarize the relationship between lava types and the force of volcanic eruptions. • Describe the major types of pyroclastic material. • Identify the three main types of volcanic cones. • Summarize the events that may signal a volcanic eruption.

  11. VOLCANIC ERUPTIONS

  12. VOLCANIC ERUPTIONS Mafic lava textures: pahoehoe: “ropy”; forms as lava first forms a crust aa: jagged chunks; forms when crust is too thick pillow lava: lava that cools very quickly, usually underwater.

  13. Pahoehoe lava

  14. Aa lava

  15. Pillow lava

  16. KINDS OF ERUPTIONS

  17. “Quiet” eruptions: Mafic lavas flow more easily gases escape easily lava flows out onto the surface Explosive eruptions: Felsic lava is thicker gasses cannot escape easily gas pressure builds up and creates a more violent eruption pyroclastic material is thrown into the air. KINDS OF ERUPTIONS FOR EACH TYPE OF LAVA

  18. VOLCANIC ROCK FRAGMENTS Pyroclastic Material • Associated mainly with felsic eruptions because they are explosive. • Dust: less than .25 mm in diameter; can travel completely around the Earth in the upper atmosphere • Ash: less than 2 mm diameter • Lapilli: less than 64 mm diameter • Blocks: larger than 64 mm; some as big as a house • Bombs: formed when lava is thrown into the air and solidifies while in the air

  19. VOLCANIC CONES

  20. Shield Volcano Here are 4 of the volcanoes that make up the big island of Hawai'i. They are Mauna Kea (MK), Mauna Loa (ML), Hualalai (H), and Kohala (K). The photo was taken from near the summit of East Maui volcano (EM). These are the largest volcanoes on Earth

  21. Cinder Cone

  22. Composite Cone Popocatepetl

  23. Fujiyama, Japan Mt. Merapi, Indonesia Mt. Merapi, Indonesia Mt. St. Helens, Washington Mt. St Helens, Washington Mt. Shasta, California Mt. Shasta, California

  24. VOLCANIC FEATURES craters and calderas • crater = the funnel shaped pit at the top of a volcanic vents • caldera = when the magma chamber below a volcano is emptied, the volcanic cone may collapse leaving, a large basin shaped depression

  25. crater VOLCANIC FEATURES

  26. caldera VOLCANIC FEATURES

  27. Caldera Formation

  28. What controls eruptions? The amount of trapped gas • When more gas is trapped, pressure builds up • MORE PRESSURE MAKES A MORE VIOLENT ERUPTION The amount of silica in the magma • Silica makes the magma thicker • Thicker magma does not flow easily so can get stuck underground, allowing pressure to build up • THICKER MAGMA MAKES A MORE VIOLENT ERUPTION

  29. Predicting Volcanic Eruptions • Increase in the number and strength of small earthquakes (magma working its way upward) • Slight bulging of the surface of a volcano (upward movement of magma just below the surface) • Information from previous eruptions

  30. 7.3 EXTRATERRESTRIAL VOLCANISM • Mars • volcanic cones on Mars • most famous is Olympus Mons • Mars seems to be seismically active • Io • one of Jupiter’s moons • has active volcanoes

  31. Fig. 22.9

  32. Fig. 22.10c

  33. Fig. 22.10a

  34. Fig. 22.11b

  35. Fig. 22.1_4

  36. Fig. 22.17

  37. Olympus Mons

  38. Io

  39. Io

  40. Fig. 22.1_2

  41. Fig. 22.14b

  42. FAMOUS ERUPTIONS • ELDFELL • MOUNT ST. HELENS • KILAUEA • VESUVIUS • MOUNT PINATUBO • CRATER LAKE

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