VOLCANOES!

Factors Affecting Eruptions Magma temperature

Hotter flows easier…

Magma viscosity – determined by temp and composition. High silica = high viscosity (thickness) High viscosity = violent eruptions…

Dissolved gases More gasses means more violent eruptions…

Volcanic Materials- Lava3 TYPES OF LAVA FLOWS

1) Aa- rough and jagged

2) Pahoehoe - wrinkly and ropey texture

3) Pillow - forms underwater at boundaries

Aa PahoehoePillow

Volcanic Materials- GasesWater Vapor, Carbon Dioxide, Nitrogen, Sulfur Dioxide, and Chlorine

Kilauea Volcano, Hawai`i From 1986-2000 emitted 1,000-2,000 metric tons of SO2 every day!

Volcanic Materials

Pyroclastic Materials = Ejected fragmentsAsh – fine material

Cinders and lapilli = medium/pebble sized

Bombs and blocks (big stuff) block = hard, bombs = lava

Ash Bombs & Blocks

Cinders

Volcanic Terms

Crater – steep walled depression at topCaldera – large depression in a volcano due to collapse of volcano

Volcanic TermsConduit – pipe connecting magma chamber to the surfaceVent – top of the conduit

Volcanic TermsLava plateau – raised flat area of lavaVolcanic neck – remnant of eroded volcano

Columbia Lava Plateau- covers parts of Washington, Oregon, and Idaho

Types of Volcanoes

Shield Volcanoesbroad base with gently sloping sides

Huge in size, mild eruptions, mostly flows,

ex: Hawaii

Mauna Kea, Hawaii

Cinder ConeNarrow base and steep sides

-Small, violent for size, pyroclastic eruptions, ex: Mt. Paricutin, Sunset crater in AZ

Composite ConeMedium base and moderately sloped size (volcano looking)

Medium size, violent eruptions, andesitic lava, combination of flows and pyroclastic eruptions, ex: Mt. St. Helens

Mt. St. Helens Before & After

Igneous ActivityPlutons (intrusive igneous bodies) Classified by shape, size, and relationship

to surrounding rock layers Sill – horizontal and between rock layers Dike – vertical and cut across rock layers Laccolith – dome/mushroom shaped plutons Batholith – more than 100 km2 of exposed

rock Stock – less than 100 km2 of exposed rock

Volcano DangersPyroclastic flows – hot gases, glowing ash, and larger rock fragments Very hot (like cook your butt hot) Can attain 200 km/hr

Lahars – mudflow formed from volcanic ash and water (melted snow or rain)

Eruptions – you’re there one minute and gone the next…can you say vaporized

Origin of Magma

Read pages 291 – 292 The role of heat The role of pressure The role of water

Volcano LocationsConvergent plates Subducting plate melts and magma rises

Japan and Mt St Helens

Divergent plates Plate diverge and magma rises through the rift

Mid-ocean ridge Iceland East African Rift

Intraplate (hot spots) Mantle plume rises towards the surface

Hawaii and Yellowstone