Transcript Plate Tectonics and Volcanoes

Tuesday, November 9th, 2010
• Learning Targets
– Describe how plate tectonics influence the formation
of volcanoes
– Identify the parts of a volcano
– Locate major zones of a volcano
• Homework
– Ch. 18.1 LTs due tomorrow
• Q.O.D
– What are volcanoes?
Plate Tectonics and
Volcanoes
Earth Science
Chapter 18
Volcanoes
• What are volcanoes?
– Opening in Earth’s crust through which molten
rock, gases, and ash erupt and the landform
that develops around this opening.
Zones of Volcanoes
Convergent Volcanism• Most volcanoes located on land result
from ocean-continental subduction
• Explosive eruptions
• 2 major belts– Circum-Pacific Belt (Ring of Fire)-outlines
west coasts of NA, SA, Aleutian Islands, east
coast of Asia
– Mediterranean Belt- outlines boundaries
between Eurasian, African, Arabian plates
Zones of Volcanism
Divergent Volcanism-magma rises to fill in
ocean gap.
• Occurs at ocean ridges.
• Non-explosive, large amounts of lava.
• 2/3 of volcanism occurs underwater at
divergent boundaries.
Zones of Volcanism
• Hot spots-Occur far from boundaries, high
temperature plumes of magma.
• Plumes stay stationary but the plates
move
• Forms a chain of volcanoes
Hot Spots
• What is Magma
– Molten rock that is below the surface of the
earth
– Located in the mantle
– Forms when rocks melt due to subduction
• What is Lava
– Molten rock that has reached the surface of
the earth
– Forms when volcanoes erupt
• What is magma/lava made of?
– Silica
– Water
– Magnesium
– Iron
• What are the different types of
magma/lava?
– Granitic (Felsic)
• Made of 70% or more silica
• High viscosity
– Basaltic (Mafic)
• Made of 50 % or less silica
• Low viscosity
• What does granitic(Felsic) magma look
like?
– Light in color
– Contains a lot of water
– Does not flow easily
– Highly viscous
– Often solidifies before reaching the earth’s
surface
• What does basaltic (mafic) magma look
like?
– Dark in color
– Flows easily
– Does not contain a lot of water
• What are the different kinds of eruptions?
– Pyroclastic-Convergent with Subduction
• Highly explosive
• Felsic
• Lots of “stuff”- Organized by size
– Bombs
• Extremely large chunks erupted from volcano
– Lampilli
• Smaller than bombs
– Ash
• Fine grained/very small chunks
• Non-Pyroclastic- Divergent
– Non-explosive
– Mafic lava
– Mid-Atlantic Ridge is best example
– Hawaii Islands
• What are the different types of volcanoes?
– Shield cone
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Broad or wide
Not very tall
Mellow eruptions
Hawaii
– Cinder cone
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Narrow
Tall
Pyroclastic eruptions
Mexico City
– Composite Cone
• Alternating layer of lava and cinders (ash)
• Alternates pyroclastic and non-pyroclastic eruptions
• Mount St. Helens
Plutonic Activity
– Solidification of magma in the earths crust
– Hardens in any existing rock
– Types
• Batholiths
– Magma exposed at the earth’s surface
– Largest
– Exposed at the surface due to erosion
• Stock
– Magma exposed at the earth’s surface
– Smaller than batholiths
– Exposed due to erosion
• Dike
– Magma cools inside a fracture (break in the crust with no
movement)
– Cut across vertically
• Sill
– Magma goes into rock layers horizontally
• Laccolith
– Magma goes into rock layers horizontally
– Hardens and makes a dome like structure
Plutonic Activity
Ring of Fire
Mafic Lava
Felsic Lava
Stages of Cinder Cone
Cinder Cone
Sunset Crater
Composite Cone
Mt Fuji, Japan
Shield Cone
Galapagos Islands
Volcanoes