1. Volcanoes

2. Volcano
Magma
-weak spot in crust where magma comes up
-molten mixture of rock-forming substance, gases, water from the mantle
-called lava on surface
-lava forms solid rock when cooled

3. Volcanic belt
Ring of Fire
-forms along plate boundaries
-magma can reach surface when plates diverge/converge and fracture crust
-major volcanic belt
-rims (circles) Pacific Ocean

5. Island Arc
-string of volcanic islands
-formed from subduction at converging oceanic plates
-ex. Japan, Caribbean Islands

7. Hot Spots
-where magma melts thru crust
-found in middle of plates and along boundaries
-volcanoes can form above hot spot
-ex. Hawaiian Islands

9. Properties of Magma Viscosity Viscosity of Magma
-resistance of a liquid to flow
-greater viscosity, slower it flows
-depends on silica content and temperature

10. Silica Content
-made of oxygen and silicon
-one of the most abundant materials in crust
-more silica = higher viscosity (sticky, flows slow)
-less silica = low viscosity (flows quickly)

11. Temperature
-viscosity increases as temp decreases
-hotter magma flows faster
-cooler flows slower

12. Volcanic Eruptions Magma reaches the surface
-materials in asthenosphere under great pressure
-liquid magma less dense than solid material around it
-flows upward until opening in rock allows to magma to reach surface

13. Inside a Volcano
Magma Chamber
Pipe
Vent
-pocket that collects magma
-tube that connects chamber to surface
-opening thru which molten rock and gas leave
-central vent at top
-sometimes, side vents on sides

14. Lava Flow
Crater
-area covered by lava as pours out of vent
-bowl-shaped area that may form at top around central vent

16. Eruption
-gases in magma under lots of pressure
-gases expand and form bubbles, as magma rises to surface
-when erupts, force of gas pushes magma from chamber thru pipe until it flows or explodes out of vent

17. Quiet Eruptions
-low silica; low viscosity; flows easily
-oozes out quietly and flows for many km
-sets fire to and buries everything in path
-produces both pahoehoe & aa
-ex. Hawaiian islands

19. Explosive Eruptions
-high in silica; high viscosity; thick/sticky
-builds up in pipe; plugs it like a cork
-trapped gases build up pressure until they explode
-breaks lava into fast cooling pieces

20. -volcanic ash: smallest; fine, rocky particles
-cinders: pebble-sized
-bombs: large pieces; baseball-sized to size of car
-ex. Mount St. Helens

21. Pyroclastic Flow
Life Cycle
-explosive eruption hurls out mixture of hot gases, ash, cinders, bombs
-active: live; erupting or showing signs of erupting in near future
-dormant: sleeping; expected to awaken in future and become active
-extinct: dead; unlikely to erupt again

22. Shield Volcanoes
-wide, gently sloping mountain made of layers of lava from quiet eruptions
-ex. Hawaiian islands

24. Cinder Cone Volcano
-steep, cone-shaped hill or small mountain made of volcanic ash, cinders, bombs piled up
-ex. Paricutin

26. Composite Volcanoes
-tall, cone-shaped mountain in which layers of lava alternate with layers of ash/other materials
-ex. Mount St. Helens

28. Calderas
-huge hole left by a collapsing volcano
-enormous eruptions empty the vent and chamber, leaving it hollow with no support
-sometimes fill with rain water
-ex. Crater Lake in Oregon