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 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_2 0110808b.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

Ash plume

Volcanic ash

Ash cloud

cinders

Volcanic block

Volcanic block

Volcanic bombs

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_04Aug 2011.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

Cinder Cone

Cinder cone (new Guinea)

Stromboli, Italy

Shield volcano (Hawaiian islands, galapagos islands Broad, slightly domed Produced by the build-up of fluid, basaltic lava

Shield Volcano, mauna loa hawaii

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 (mt st helens) Large symmetrical structures composed of layers of lava and pyroclastic materials Silica rich, viscous lava Most explosive, ejects large amounts of pyroclastic materials

Mt. St. helens after eruption

Composite cones (mt st helens, krakatoa, mt ranier) Ring of Fire – string of volcanoes around the rim of the Pacific Plate

Composite cones (mt st helens, krakatoa, mt ranier) Pyroclastic flow: Very hot clouds of pyroclastic materials and gases rushing down slopes at speeds up to 200 Km/hr

Composite cones (mt st helens, krakatoa, mt ranier) 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

Mt st helens

Mt pinatubo ash blocking sunlight

Pompeii with mt vesuvius in background Pompeii with mt vesuvius in background. The pyroclastic flow buried the city and its inhabitants

Victims of mt Vesuvius

Gases: Mt Pinatubo sulfer dioxide cloud nine days after eruption

Lahar/mudslides and erosion from mt st helens

Scientists measuring erosion from mt st helens lahar

Mt st helens lahar damage

Lava flow damage

Newberry volcano lava flow