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Volcanoes. Chapter 18 Page 498. 18.1 Zones of Volcanism. Volcanism = describes all the processes associated with the discharge of magma, hot fluids and gases. Ring of Fire. Active volcanoes that create a “ring” pattern in the pacific ocean

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volcanoes

Volcanoes

Chapter 18

Page 498

18 1 zones of volcanism
18.1 Zones of Volcanism
  • Volcanism = describes all the processes associated with the discharge of magma, hot fluids and gases.
ring of fire
Ring of Fire
  • Active volcanoes that create a “ring” pattern in the pacific ocean
  • Typically volcanoes from convergent and divergent boundaries.
convergent volcanoes
Convergent Volcanoes
  • Volcanoes that form from plates colliding or subducting.
  • Land volcanoes tend to be explosive
divergent volcanism
Divergent Volcanism
  • 2/3rds of volcanism underwater
  • The ocean ridges that form tend to release giant pillow lava.
  • Tend to be non-

Explosive and large

hot spots
Hot Spots
  • Volcano that forms NOT at a plate boundary.
  • Magma rises from HOT areas of the mantle
flood basalts
Flood Basalts
  • From hot spots below the continental crust
  • Basalt rises up along cracks called FISSURES.
  • Often leaves a PLATEAU structure behind.
anatomy of a volcano
Anatomy of a Volcano
  • Conduit = tube
  • Vent = opening
  • Crater = depression

around the vent

calderas
Calderas
  • Large crater that may have formed from a large explosion.
  • Sometimes forms into a lake
types of volcanoes
Types of Volcanoes
  • 1. Shield Volcanoes
  • 2. Cinder Cones
  • 3. Composite Volcanoes
  • All three depend on 2 factors:
    • Type of material that forms it
    • Type of eruption
shield volcano
Shield Volcano
  • Broad, gently sloping, circular base
  • Largest type
  • Nonexplosive eruption which leaves layers of lava.
cinder cone
Cinder Cone
  • Formed from eruptions that eject small pieces of magma from the air.
  • The small pieces pile back around the vent causing the cinder cone shape.
  • Small and steep
composite volcanoes
Composite Volcanoes
  • Violent eruptions
  • Formed by layers of hardened chunks of lava from the eruptions alternating between explosions and oozing of lava
  • Cone shaped with

concave slopes

(larger than cinder)

18 2 explosive eruptions
18.2 Explosive Eruptions
  • Tephra = is the erupted material from the volcano.
  • Can be solidified lava OR pieces of crust
  • Classified by size:
      • Less than 2 mm is called ASH
      • Largest is called BLOCKS
explosion effects
Explosion effects
  • Ash can rise into atmosphere hurting:
    • Airplanes
    • Change in weather - Block sun’s rays therefore lower temps
proclastic flows
Proclastic Flows
  • Clouds of ash and other tephra
  • Travels at speeds of 125 mph
  • Mixed with hot gases
  • up to temps of 700*C
  • Can kill thousands AFTER

the explosion