Lecture Notes 16 Volcanoes .doc

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11 Apr 2012
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Lecture 16
Volcanoes
20% of population lives near volcano
Soils produced by volcanoes are highly fertile and farmers live close to volcanoes
but face the risk of volcanoes
Volcano Types
Shield volcano- Mauna Loa, Hawaii largest individual mountain 400 metres above
sea level
Cinder cone- Pu’u (hill) O’o ( extinct bird), Hawaii they are round, craters at the
top which represent a vent
Mt.St. Helens, Washington - composite cone or stratovolcano , material blown in
the air eruptions
Calderas: Example: Aniakchak caldera Alaska: collapsed of an existing volcanoes
due to eruption and evacuation of magma reservoir
Shield Volcanoes: 3 Hazards
Lava Flows
Gas emissions
Faults, earthquakes, tsunamis
The Big Island
3 active volcanoes
1 dormant volcano
1 extinct volcano
Kilauea Volcano
Typical eruption, Halemaumau
An atypical explosive eruption, Halemaumau, 1924; lava lake level dropped, al-
lowed groundwater into lake
Now: First explosive eruption since 1924
La Palma, Canary Islands
1949 eruption opened 2 km-long fracture along Cumbre Vieja, west side slumped
few metres towards sea
Cinder Cones
Craters of the Moon, Idaho
Lava flows Cinder Bombs Blocks
Paricutin, Mexico 1943-1952
Lavas cover 10 square miles 4 towns destroyed, No deaths
Bombs: Blobs of molten lava
Blocks: fragments of existing volcanic structure
Composite cones
Lava flows pyroclastic flows Ash/pumice falls Bombs, blocks Volcanic gases Land-
slides Lahars Earthquakes
Pyroclastic flow: fast moving cloud of hot gas, ash, magma (pumice) and rock frag-
ments
1902: pyroclastic flow from Mt. Pelee destroys village of St. Pierre, Martinique; 29,
000 dead
Eruption clouds: ash pumice blown into air, eventually falls to ground
1991: Mt. Pinatubo, philippines Ash hazard to aircraft in air, on ground!
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