Download Volcanoes

Volcanoes
Anatomy of a Volcano
• Conduit (pipe) in
center
• Vent on top
• Crater = steep-walled
depression
Magma
• Some magmas
have dissolved
gasses in them
• Gasses rise &
cause pressure
– Like a soda bottle
Viscosity
– A substance’s resistance to flow
• Determined by
– Composition – type of rock (more silica = higher viscosity)
• Basaltic Lava = not viscous
• Andesitic Lava = very viscous
– Temperature – cooler temperatures = higher viscosity
– The more viscous the more explosive the eruption
Eruptions
• The most viscous
(cold, silica) gassy
lavas have the
greatest eruptions
Types of Volcanos
1. Shield Volcanoes
Are broad, slightly domed
structures
Produced by fluid
basaltic lavas
Some form islands in ocean
(ex. hawaii & iceland)
2. Cinder Cones
Eject lava fragments the
size of cinders into the air
High in gas-rich basaltic
magma
small, usually only erupt
once (maybe a few times)
3. Composite Cones
gas rich magma with andesitic composition (lots of
silica) – causes very viscous lavas
have explosive eruption
Found in the Pacific Ocean called “The Ring of Fire”
Hot Spots
• A rising mantle
plume that melts
surface rocks
creating volcanoes
Hot spots – Evidence for Plate
Tectonics
• The hot spot stays in one
place…then the plate
moves…the hot spot is still
there so a new volcano
forms
• Eventually there is a line of
volcanoes – the oldest
being further away from the
hot spot
• Example is line of
volcanoes from Suiko to
Hawaii (Suiko is oldest,
Hawaii is youngest)