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volcanoes. Volcano . Definition: A mountain formed of lava or pyroclastic material. Redoubt Volcano. Aleutian Islands, Alaska. Factors affecting eruptions. Viscosity – a substance’s resistance to flow Thickness of lava depends on it’s chemical composition Silica increases viscosity
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Volcano Definition: A mountain formed of lava or pyroclastic material.
Redoubt Volcano Aleutian Islands, Alaska
Factors affecting eruptions • Viscosity – a substance’s resistance to flow • Thickness of lava depends on it’s chemical composition • Silica increases viscosity • Rhyolitic (contains Rhyolite) - high silica content = high viscosity • Basaltic (contains Basalt) – low silica content = low viscosity
Factors affecting eruptions • Viscosity – a substance’s resistance to flow • Thickness of lava depends on it’s chemical composition • Silica increases viscosity • Rhyolitic (contains Rhyolite) - high silica content = high viscosity • Basaltic (contains Basalt) – low silica content = low viscosity
Factors affecting eruptions • Viscosity – a substance’s resistance to flow • Thickness of lava depends on it’s chemical composition • Silica increases viscosity • Rhyolitic (contains Rhyolite) - high silica content = high viscosity • Basaltic (contains Basalt) – low silica content = low viscosity
Volcanic material • Gases • Composition • 70% water vapor • 15% Carbon Dioxide • 5% Nitrogen • 5% Sulfer • Other gases – Chlorine, Hydrogen, Argon
Dissolved gases • Mostly water and carbon dioxide • High silica Rhyolite traps more gas • Low silica Basalt releases gas • Trapped gases create pressure that leads to more • http://hvo.wr.usgs.gov/kilauea/update/archive/2011/Mar/Overflight_20110808b.mov
Volcanic materials • Lava Flows • Pahoehoe – very fluid, basaltic, looks rope-like when it cools http://hvo.wr.usgs.gov/kilauea/update/archive/2011/Mar/20110923_torr_2609_trim.MOV
Volcanic materials AA (ah-ah) – rough, jagged, very slow moving
Volcanic material • Pyroclastic Materials • Particles produced by volcanic eruptions • Ejected from the vent • Includes: • Dust and Ash (less than 2mm in dia.) • Cinders (2mm – 64mm in dia.) • Blocks and Bombs • greater than 64mm • Can weigh tons • Blocks are hardened • Bombs are molten
Types of Volcanoes • Anatomy of a volcano • Crater – steep walled depression at the summit
Types of Volcanoes • Anatomy of a volcano • Fissure – crack in the Earth’s crust that magma moves through
Types of Volcanoes • Anatomy of a volcano • Pipe • tube through a volcano that magma moves through
Types of Volcanoes • Anatomy of a volcano • Vent – opening on the surface where lava flows or is ejected • http://hvo.wr.usgs.gov/kilauea/update/archive/2011/Mar/SpatterVents_04Aug2011.mov
Types of Volcanoes • Anatomy of a volcano • Magma Chamber – A large reservoir of magma within the Earth’s crust
Cinder cone • SC Volcano Arizona, Stromboli Italy • Cinder sized fragments ejected into the air, harden and collect into a steep mound • Eruptions can last from several days to several years • When eruptions stop, magma in the pipe and chamber hardens and the volcano never erupts again • Several cinder cones can form fields others can form on the sides of larger volcanoes
Shield volcano (Hawaiian islands, galapagos islands • Broad, slightly domed • Produced by the build-up of fluid, basaltic lava
Shield volcano (Hawaiian islands, galapagos islands • Hot Spots – locations where a volcanic plume rises to the surface, far away from plate boundaries, usually under oceans to build island chains as the plate moves
Hawaiian Island progression is toward Northwest as the pacific plate moves
Composite cones (mtsthelens) • Large symmetrical structures composed of layers of lava and pyroclastic materials • Silica rich, viscous lava • Most explosive, ejects large amounts of pyroclastic materials
Composite cones (mtsthelens, krakatoa, mtranier) • Ring of Fire – string of volcanoes around the rim of the Pacific Plate
Composite cones (mtsthelens, krakatoa, mtranier) • Pyroclastic flow: Very hot clouds of pyroclastic materials and gases rushing down slopes at speeds up to 200 Km/hr
Composite cones (mtsthelens, krakatoa, mtranier) • Lahar: Destructive mudflows created from water-saturated volcanic debris
Other volcanic landforms • Caldera: large depression formed by collapsing volcanoes (ie…Crater Lake Oregon, Yellowstone Park Wyoming)
Other volcanic landforms • Volcanic Neck: hardened magma remaining after the volcanic cone erodes away
Other volcanic landforms • Volcanic Pipe: remain years after a volcano becomes extinct (diamonds can form there)
Other volcanic landforms • Lava Plateaus: deposits of volcanic material flowing from fissures or rifts
Global affects of volcanic activity • Ash http://geology.com/articles/volcanic-ash.shtml • can spread over wide areas and affect temperatures, soil composition, drainage, etc… • can be thick enough to block out the sun • Is extremely abrasive and can be destructive to machinery( small enough to pass through air filters and get into car engines) • Can smother plants interrupting photosynthesis
Global affects of volcanic activity • Ash (continued) • Can disrupt air traffic • Has been known to disable aircraft in flight
Pompeii with mt vesuvius in background. The pyroclastic flow buried the city and its inhabitants
Gases:Mt Pinatubo sulfer dioxide cloud nine days after eruption