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Volcanic Eruptions 3.3

Volcanic Eruptions 3.3. Objectives: Explain what happens when a volcano erupts. Describe 2 types of volcanic eruptions Identify stages of volcanic activity. Volcanic Eruptions 3.3. What comes out of volcanic explosions? Ash, lava, steam, rock, gases, dirt Magma forms in the asthenosphere

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Volcanic Eruptions 3.3

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  1. Volcanic Eruptions 3.3 • Objectives: • Explain what happens when a volcano erupts. • Describe 2 types of volcanic eruptions • Identify stages of volcanic activity

  2. Volcanic Eruptions 3.3 • What comes out of volcanic explosions? • Ash, lava, steam, rock, gases, dirt • Magma forms in the asthenosphere • Convection currents in the mantle bring magma towards the surface • Magma tries to flow into any open crack • When magma reaches a weak spot in the crust, a volcano forms • Lava is magma that has reached the surface

  3. Magma Reaches Earth’s Surface • Volcanoes are systems of passage ways through which magma moves. • Inside a Volcano • Magma collects below the volcano in the magma chamber • Magma flows upward through a tube (pipe) that connects the magma chamber to the surface.

  4. Magma Reaches Earth’s Surface • Inside a Volcano • Gas and magma leave through vents • Central vent is the opening at the top • Side vent anywhere along the side of the volcano • Lava pours out of the vents and creates a lava flow • A bowl shaped area called a crater may form around the central vent

  5. Crater Vent Pipe Side Vent Lava Flow Magma Chamber

  6. Magma Reaches Earth’s Surface • A Volcanic Eruption • Dissolved gases are trapped in magma under extreme pressure (CO2 in a soda bottle) • as magma flows , pressure because there is less rock on top of it. • the dissolved gases expand and form bubbles • When a volcano erupts, the force of the expanding gas forces magma up the pipe until it explodes out the vent

  7. Content checkpoint… think/pair share…take two minutes to answer these questions with a partner nearby….. • What common everyday occurrence can we relate to a volcanic eruption? • What happens to the pressure in the magma as it rises toward the surface?

  8. Kinds of Volcanic Eruptions • Volcanic eruptions can be quiet or explosive. • Eruptions depend on the properties of magma • Silica content • Viscosity

  9. Kinds of Volcanic Eruptions • Quiet Eruptions • Magma has low silica content = low viscosity • Magma flows easier so gases bubble out gently • Lava can flow many kilometers from the vent • Produce both pahoehoe and aa lava • Example: Hawaiian Islands – Mount Kilauea

  10. Kinds of Volcanic Eruptions • Explosive Eruptions • Magma has high silica content = high viscosity • Magma doesn’t always flow out of vent and so it builds up (like a cork in a bottle) • Trapped gases build up pressure until they explode • Magma is pushed out of the vent with incredible force

  11. Kinds of Volcanic Eruptions • Explosive Eruptions • Lava breaks into fragments that cool quickly and harden into different sizes • Ash – fine, dust sized particles of lava • Cinders – pebble sized particles • Bombs – baseball to car sized chunks of lava • Pyroclastic flow:when an explosive eruption hurls out gases, ash, cinders and bombs. • Pumice forms when lava cools quick and traps air bubbles inside • Obsidian forms when lava cools quick leaving the surface smooth and glass-like

  12. Kinds of Volcanic Eruptions • Volcano Hazards • Quiet eruptions cause lava to flow far --- burning and burying everything in its path • Explosive eruptions can bury entire towns in ash, cause landslides, avalanches, cause damage from gases and cinders/bombs.

  13. Content checkpoint… think-pair-share take two minutes to answer these questions with a partner nearby. • What is pyroclastic flow? • How does volcanic ash cause damage? • What is the main difference between a quiet eruption and an explosive eruption?

  14. Stages of Volcanic Activity • Life Cycle of a Volcano • Scientists use historical records and monitor volcanoes to determine what stage of activity a volcano is in • A volcano can be active, dormant or extinct • An active volcano is erupting or showing signs of near future eruptions • A dormant (sleeping) volcano can awaken in the future and become active • An extinct (dead) volcano is unlikely to erupt ever again

  15. Stages of Volcanic Activity • Monitoring Volcanoes • Geologists use tiltmeters to detect slight changes in surface elevation cause by magma moving underground • They monitor gases escaping from a volcano • Increase in temperature might mean magma is nearing the surface • The changes detected may give a short warning time BUT • We cannot be certain the type of eruption or how powerful it will be

  16. Think and Discuss…. • Which is more likely to be dangerous – a volcano that erupts frequently or a volcano that has been inactive for a hundred years? WHY?

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