VolcanoesObjective: Understanding what causes volcanoes and the different types they form.

Volcanoes

• Volcanic Explosion Volume• Determined by • The amount of gases trapped in the

magma • The composition of the magma

Volcanoes

• Granitic Magma = Loud/Explosive Eruption• Contains more silica• Higher water content• More viscous (sticky)• Hawaiian Islands

• Basaltic Magma = Quiet Eruption• Contains less silica• Less viscous (sticky)• Mount St. Helens

Volcanoes

• Andesitic Magma = Explosive• Medium silica content• Medium viscosity (stickiness)

Volcano Types

• Volcano Types• Composite (Stratovolcano)• Alternating layers of silica lava and tephra

(cinder) eruptions

• Cinder Cone• Tephra (cinder) piles up in steep sided cone

• Shield Volcano• Broad volcano with gently sloping sides;

quiet basaltic eruptions

Volcano Vocabulary

• Batholith• Largest intrusive rock bodies• Form when a large plume of magma

cools underground

Volcano Vocabulary

• Dike• Magma squeezes into a vertical crack

• Sill• Magma squeezes between horizontal

rock layers

Volcano Vocabulary

batholith

laccolith

sill

dike

Volcano Vocabulary

• Volcanic Neck• Weathering and erosion remove the sides

of the volcano leaving the solidified vent behind

Volcano Vocabulary

• Caldera• When the top of the volcano collapses

after a large eruption