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COURSE LECTURE NOTES:

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VOLCANOES

Definitions

    volcano - collection of igneous material around a vent

    vent - hole that emits igneous material

    igneous material - Rx & glass formed from melt

    magma - melted rock with gas and maybe some crystals, starts 40 - 100 km below surface, loses gas when it reaches surface and becomes lava.

The three things that are emitted by a volcano

    1. lava - liquid flow of magma near the surface that has lost the gas content

    2. gas - there are several different kinds


    3. pyroclastic material -



Magma (melted rock) - types (all are part of continuum)
Type SiO2 Fe Color Viscosity Flow Explosiveness Lava Type Melt Temp Example
basalt 50% 15% dark (black) low 1/2 - 3 mph low basalt high 20% 900o C Mauna Loa
andesite 60% 8% grey medium medium medium mixed medium 15% 1000oC Mt St. Helen
rhyolite 70% 2% light
white & others
high slow high pyroclastic low 10% 900oC Krakatau

Types of volcanoes

    1. Shield - basalt, very hot lava flow, gentle eruption with fire fountains. Slope usually < 10o

    Examples:


    2. Complex (aka stratovolcano, composire cone)- layers of basalt and pyroclastic materials

    Examples:

    3. Resurgent caldera - leaves a huge hole

Additional types of volcanoes (old lava)

    A. Pyroclastic cone (aka cinder cone) - a steep (up to 40o, conical hill of pyroclastic materials (any type of lava) that accumulate around and downwind from a vent (shape may be distorted by wind). Most common volcano

    Examples:


    B. maar - hole in the ground. Old lava forced out by new lava. Phreatomagmatic eruption
    Examples:

    C. Dome - a mound, has to be andesite or rhyolite (on Earth)

    Examples:


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