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Volcanic eruptions

Volcanic eruptions. Volcanoes. Volcanoes Areas of Earth’s surface through which magma & volcanic gas passes Creative Forces forming fertile farmland & large mountains Destructive Forces Turning mountains into clouds of ash & rock, destroying forests & homes.

joshua-hebert
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Volcanic eruptions

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  1. Volcanic eruptions

  2. Volcanoes • Volcanoes • Areas of Earth’s surface through which magma & volcanic gas passes • Creative Forces • forming fertile farmland & large mountains • Destructive Forces • Turning mountains into clouds of ash & rock, destroying forests & homes

  3. Structure of a typical volcano. Notice the alternating layers of ash and hardened lava. Why does this occur?

  4. Structure • Inside a Volcano • Magma • Body of molten rock (underground) that feeds a volcano • Vents • Opening through which volcanic material passes

  5. Volcanic Eruptions • Nonexplosive Eruptions • Most common type of eruption • Release large amounts of lava • Calm lava flow • Pacific NW of USA covered from these eruptions

  6. Volcanic Eruptions • Explosive Eruptions • Rare & incredibly destructive • Debris/molten rock blown out of volcano • Large debris falls close to volcano • Smaller, dust-sized particles (ash) can travel miles

  7. Volcanic Eruptions • Magma • Molten rock • Composition affects how explosive a volcano is • Silica (SiO2), Water, Gases (CO2, water vapor) • When pressure decreases as magma rises, the CO2 and water vapor expand rapidly • Silica Rich (Felsic) Magma Traps Gases • Thicker, viscous • Difficult for gases to escape, so pressure builds up

  8. Volcanic Eruptions • What Erupts from a Volcano? • Explosive Volcano • Mainly pyroclastic material • Magma that is blasted into the air and hardens • Nonexplosive Volcano • Mainly lava Eruptions can (and do) alternate between lava & pyroclastic eruptions (even within the same eruption)

  9. Volcanic Eruptions • Types of Lava • Aa jagged surface; brittle crust is torn by lave flow underneath • Pahoehoe flows slowly; glassy surface has rounded wrinkles • Pillow Lava rounded lumps formed under water • B locky Lava does not travel far; heaps of sharp-edged chunks

  10. Volcanic Eruptions • Types of Pyroclastic Material • Formed when magma explodes and solidifies in the air • Volcanic Bombs • Large blobs that cool & harden in the air • Lapilli • Smaller, pebble-like stones that harden before hitting the ground • Volcanic Ash • Most of the material in an eruption • Walls of gas bubbles explode into tiny, glass-like slivers

  11. Volcanic Eruptions • Pyroclastic Flows • Produced when enormous amounts of hot ash, dust, and gases are ejected from a volcano • Speeds up to 200 km/h • Temperatures over 700 C

  12. Volcanic Eruptions • Review What factors influence whether a volcano erupts explosively?

  13. Volcanic Eruptions • Review 2) How is lava classified? How are pyroclastic materials classified? 3) Explain how the presence of silica (felsic) and water in magma increases the chances of an explosive eruption.

  14. Volcanic Eruptions • Answers 1) Pressure of gases, viscosity of magma, silica content, water, gases 2) Lava is classified by its surface texture; the way it flows may also be used to help classify lava. Pyroclastic material is classified by its size and how it forms. 3) As the magma moves towards the surface, the water changes to water vapor and expands rapidly; silica rich (felsic) magma is viscous and tends to trap volcanic gases and plug vents, the results in high pressures forming

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