Let’s Review… Copy in Notebook and Answer: Compare and contrast magma and lava. What plate boundaries will result in formation of a volcano?

What caused Mt. St. Helen’s to erupt? Magma What 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 Silica Content Gas Content Type of Volcano Example Viscosity Silica Content Gas Content Explosive-ness Type of Volcano Example    

Hawaii Basaltic Low 1-2% 50% Least Shield Type of Magma Silica Content Viscosity Silica Content Gas Content Explosive-ness Type of Volcano Example   Hawaii Basaltic Low 1-2% 50% Least Shield  

Hawaii Basaltic Low 1-2% 50% Least Shield Andesitic Medium 3-4% 60% Type of Magma Viscosity Silica Content Gas Content Explosive-ness Type of Volcano Example   Hawaii Basaltic Low 1-2% 50% Least Shield Mt. St. Helens Andesitic Medium 3-4% 60% Composite Medium  

Hawaii Basaltic Low 1-2% 50% Least Shield Andesitic Medium 3-4% 60% Type of Magma Viscosity Silica Content Gas Content Explosive-ness Type of Volcano Example   Hawaii Basaltic Low 1-2% 50% Least Shield Mt. St. Helens Andesitic Medium 3-4% 60% Composite Medium Cinder Cone Rhyolitic High Greatest 4-6% 70% Yellowstone *The higher the gas content, the more explosive the magma is going to be

Volcanic Material Tephra Pyroclastic Flow 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