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

Hazard

Year Volcano Country Deaths

1991 Pinatubo Philippines 300 (200,000 evaq.)

1985 Ruiz Colombia 23,000

1902 Pelee Martinique 28,000

1883 Krakatau Indonesia 36,000

1815 Tambora Indonesia 92,000

1792 Unzen Japan 14,500

Future hazard Population near big, recently active volcanoes

– Seattle– Mexico City– Quito– Indonesia– Japan

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

1. Shield Volcanoes – Hawaii, Iceland– Basaltic

2. Stratovolcanoes (or composite)– Mt. Saint Helens, Pinatubo, etc– Andesitic– Explosive

Shield Volcanoes

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

Stratovolcanoes(composite)

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

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

Phreatic (vapor) eruption

Bulge

Mt. St. HelensPyroclastic

Eruption

After the eruption

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

Pyroclastic eruption

Volcanic landscape: A Caldera (Crater Lake)

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

Plate Tectonic Settings of Volcanism

Plate tectonic settings of volcanoes