Section 9.2 Volcanic Eruptions. What FACTORS determine if a volcano erupts violently or quietly?
Volcanic Eruptions and Volcano Type. What is a volcano? A volcano is any place where gas, ash, or...
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Transcript of Volcanic Eruptions and Volcano Type. What is a volcano? A volcano is any place where gas, ash, or...
• Crater– Lava collects in the
crater, the bowl-shaped area that forms around the volcano’s vent.
Volcano Menu
CraterVent
Lava Flow Pipe
Magma chamber
Side Vent
• Vent– The point on the
surface where magma and gas leave the volcano’s pipe.
Volcano Menu
CraterVent
Lava Flow Pipe
Magma chamber
Side Vent
• Pipe– A narrow, almost
vertical crack in the crust through which magma rises to the surface.
Volcano Menu
CraterVent
Lava Flow Pipe
Magma chamber
Side Vent
• Magma Chamber– A large underground
pocket of magma that forms from magma rising to the surface.
Volcano Menu
CraterVent
Lava Flow Pipe
Magma chamber
Side Vent
• Lava Flow– The river of lava
that pours down a volcano over the land.
Volcano Menu
CraterVent
Lava Flow Pipe
Magma chamber
Side Vent
• Types of Volcanic Eruptions– A volcano’s magma
determines its volcanic cone and influences how the volcano erupts.
– The silica content helps determine whether the volcanic eruption is quiet or explosive.
Shield Cones and Quiet Eruptions (Examples: Grimsvotn of Iceland and Kilauea of Hawaii)
*Form as a result of sea-floor spreading or “hotspots” in the Earth’s mantle.
• Shield Cones and Quiet Eruptions– Magma flows easily.– Dissolved gases in the magma bubble out easily.– Thin runny lava oozes from the vent and flows
• Volcanic Hazards of Quiet Eruptions– Quiet Eruptions:
• Lava flows- set fire and bury everything in their path.
Composite Volcanoes and Explosive Eruptions (Examples: Mount Vesuvius of Italy and Mount Saint Helens Washington State)
*Form as a result of subduction.
• Volcanic Hazards– Time between
eruptions for composite cones can span hundreds of years.
(Dormant Volcano)– Example: Mt. St.
Helens 123 years.– People may be
unaware of the danger.
• Explosive Eruptions• Magma is thick and
sticky.• Thick magma builds up
in the pipe, plugging it like a cork in a bottle.
• Pressure builds up due to the gases in the magma until the volcano explodes.
• Volcanic Hazards of Explosive Eruptions– Lahar:
• A mud flow caused by melted snow.
– Carries ash, trees and rocks.
• Explosive Eruptions• The gases push the
magma out with incredible force.
• The explosion breaks lava into fragments that quickly cool and harden into different sizes.
• Explosive Eruptions• Fragments:
– Volcanic Ash» fine, rocky, grain of
sand sized particles.– Cinders-
» pebble sized particles– Bombs-
» large pieces of rock (baseball to the size of a car)