Volcanoes
Jan 02, 2016
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
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
Lahars (mudflows)
Very destructive Kill as many people as the eruption itself Loose ash forms mud avalanches Glaciers on top of volcano melt Rain
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