Let’s Review…

• Copy in Notebook and Answer:– Compare and contrast magma and lava.– What plate boundaries will result in formation

of a volcano?

MagmaWhat caused Mt. St. Helen’s to

erupt?

How does Magma form?

• Magma is molten rock beneath the Earth’s surface

• High Temperature:

– Rocks melt at

800-1200°C

Viscosity• Viscosity – internal resistance to flow

• Low Viscosity

– Moves fast (Less thick)

• High Viscosity

– Moves slow (More thick)

Types of Magma

Type of Magma

Viscosity Silica Content

Gas Content

Explosive-ness

Type of Volcano

Example

             

             

             

 

Type of Magma

Viscosity Silica Content

Gas Content

Explosive-ness

Type of Volcano

Example

             

             

             

 

Basaltic Low 1-2% 50% Least Shield Hawaii

Type of Magma

Viscosity Silica Content

Gas Content

Explosive-ness

Type of Volcano

Example

             

             

             

 

Basaltic Low 1-2% 50% Least Shield Hawaii

Andesitic Medium 3-4% 60% Medium CompositeMt. St. Helens

Type of Magma

Viscosity Silica Content

Gas Content

Explosive-ness

Type of Volcano

Example

             

             

             

Basaltic Low 1-2% 50% Least Shield Hawaii

Andesitic Medium 3-4% 60% Medium CompositeMt. St. Helens

Rhyolitic High 4-6% 70% Greatest Cinder Cone

Yellowstone

*The higher the gas content, the more explosive the magma is going to be

Volcanic Material

• Tephra – Rock fragments thrown into the air during a

volcanic eruption

• Pyroclastic Flow – Rapidly moving volcanic material.– Speeds up to 200km/h– May contain hot, poisonous gases

Tephra

Pyroclastic Flow

Shield Volcano• Broad Gentle Sloping Sides• Non-Explosive

Composite Volcano• Alternates Lava and Tephra• Potentially most dangerous

Cinder Cone Volcano• Steep sides caused by tephra landing around vent• Explosive