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Volcanoes : 


Volcanoes : 

Volcanoes Evidence that we live in an active planet The gods of the underworld Millions of people live near active volcanoes The greatest geological hazard

Mount Saint Helens- after : 

Mount Saint Helens- after

Hazard : 


Future hazard : 

Future hazard Population near big, recently active volcanoes Seattle Mexico City Quito Indonesia Japan

Lava : 

Lava Molten rock that flows on the surface Basaltic Lava low silica, fluid, low gas, not explosive Andesitic Lava high silica viscous gas-rich explosive

Types of volcanoes : 

Types of volcanoes 1. Shield Volcanoes Hawaii, Iceland Basaltic 2. Stratovolcanoes (or composite) Mt. Saint Helens, Pinatubo, etc Andesitic Explosive

Shield Volcanoes : 

Shield Volcanoes Huge broad cones Gentle slopes Made from lava flows Basaltic Form at hotspots Not very dangerous Predictable

Stratovolcanoes(composite) : 

Stratovolcanoes(composite) Andesitic lava Rich in dissolved gases Violent eruptions alternate with lava flows Steep-sided cones Very dangerous Unpredictable

Pyroclastic Flows : 

Pyroclastic Flows Product of explosive eruptions Hot ash shot up into the atmosphere Ash column collapses Pyroclastic flow can travel 60 mi/hr Ash can fall 100’s of miles away Ash may affect global climate

Mt. Saint Helens before : 

Mt. Saint Helens before

Phreatic (vapor) eruption : 

Phreatic (vapor) eruption

Bulge : 


Mt. St. HelensPyroclasticEruption : 

Mt. St. HelensPyroclasticEruption

After the eruption : 

After the eruption

Lahars (mudflows) : 

Lahars (mudflows)

Lahars (mudflows) : 

Lahars (mudflows) Very destructive Kill as many people as the eruption itself Loose ash forms mud avalanches Glaciers on top of volcano melt Rain

Inside a volcanoe : 

Inside a volcanoe

Slide 37: 

Pyroclastic eruption

Volcanic landscape: A Caldera (Crater Lake) : 

Volcanic landscape: A Caldera (Crater Lake)

Crater lake formation(caldera) : 

Crater lake formation(caldera) 1. Early eruptions from composite cone 2. Great eruption empties the magma chamber 3. Summit collapses 4. Caldera fills with water

Slide 44: 

Plate Tectonic Settings of Volcanism

Slide 45: 

Plate tectonic settings of volcanoes

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