GEY 101 - Introductory Geology: Exploring Planet Earth
Volcanic Activity

Volcanoes - explosive, lava flows

Controls on explosiveness

• gas content (H2O, CO2, N, SO2, H2S)
  • Affects magma mobility
  • Gases expand as the magma nears the earth surface
  • Violence is related to how easily the gases excape
• Composition -- SiO2 content -- higher silica content = higher viscosity and vice versa
• Temperature -- hotter magmas are less viscous

These control the magma viscosity. Viscosity is the measure of a material's resistance to flow.

Fluid basaltic laveas generally produce quiet eruptions where highly viscous lavas (rhyolite or andesite) produce more explosive eruptions.

Lava Flows

• Basaltic lavas are much more fluid
• Types
  • Pahoehoe -- ropey
  • Aa -- jagged blocky texture

Dissovled Gases

• 1 to 6% of a magma by wieght
• Mainly water vapor and carbon dioxide

Pyroclastic Materials

• Ash and dust
• Pumice
• Lapilli
• Cinders
• Blocks
• Bombs

General Features

• Crater
• Caldera
• Vent

Types of volcanoes

• Shield volcano -- Mauna Loa on the Island of Hawaii is an example
• Cinder cone
• Composite cone (Stratovolcano) -- associated with lahars/pyroclastic flows; form through alternate eruptions of lava and ash flows. Fujiyama, Mt St. Helens, and Mt Hood are examples of composite cones
• Calderas -- Yellowstone is one example
• Pyroclastic Flows -- Ash - Bombs, solidified lava thrown into the air.
• Fissure eruptions -- Flood Basalts, basalt Plateaus
• Lava Domes -- Rhyolites make these up
• Volcanic Pipes and Necks

Additional Study Guide

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