Thursday, February 4th, 1999
Announcements: first exam is next Thursday

Lecture notes:

I. Preview

    A. Yellowstone

        1. Earthquakes

        2. Explosive volcanoes

    B. Tectonic setting (style of eruption)

        1. Hot spot beneath CONTINENT

    C. Related topics

        1. Geysirs

        2. Calderas

        3. Rheology -- ability to flow, stickiness

            a. Eruptive styles

            b. P, S and surface waves

II. Lava types and properties

    A. Basalt (ex. Hawaii)

        1. Comes from melting the asthenosphere (hot part of mantle)

        2. 45% Silica ( SiO2 ), 8-10% Magnesium ( MgO )

        3. Very dark in color

        4. Flow properties
 
            a. Low viscosity

            b. Flows readily so eruptions are not as dangerous

        5. Formed all ocean floor (Mid Ocean Ridge system and hot spots under ocean floor)

    B. Andesite (ex. Cascades, Aleutians, Lesser Antilles, Mt. St. Helens)

        1. Has a complex origin

        2. Involves melting of some asthenosphere and some crust

        3. Found in the Andes (subduction--like volcanoes)

        4. 55% Silica ( SiO2 ), 4-5% Magnesium ( MgO )

        5. Moderate grey in color

        6. Flow properties

            a. Intermediate viscosity

            b. May flow or explode

        7. Formed in subduction environment
 
            a. Continent under ocean ( ex. Cascades)

            b. Ocean under ocean ( ex. Aleutians, Lesser Antilles )

    C. Rhyolite (ex. Yellowstone)

        1. Comes from usually melting at continental crust

        2. 70% Silica ( SiO2 ), 1% Magnesium ( MgO )

        3. Very light in color (possibly yellow or white)

        4. Flow properties

            a. High viscosity

            b. Can really blow up

        5. Hot spot under continent (can occur along continental margins)

III. Yellowstone

    A. Caldera -- a big crater (shape) formed through a volcanic eruption (30-50 miles); 50 by 50 miles is the biggest
        a caldera usually is

    B. You usually see ash (very loose rock) whereas in Hawaii you see mostly solid rock

    C. Smells like Sulfur in Yellowstone (rotten egg smell)

    D. When Sulfur and water get together they naturally form Sulfuric Acid ( pH less than 1 usually .3 pH )

    E. Geysirs -- a pool of water that is extremely hot and periodically explodes; underground it is a system of really hot
        water

        1. Needs a lot of water (rain, snow, ground water)

        2. Needs to have occasional pipes (conduit) that are really strong

        3. Pipes need to be strong because magma expands and is very pressured so the pipes need to be strong enough
            to withstand pressured water

        4. Cold water causes pressure with the hot water because the cold water is so heavy

IV. Earthquakes

    A. Common, small events (magnitude of less than 3.0)

    B. Rare, large events (magnitude greater than 6.0)

    C. Swarms of earthquakes associated with magma transport

    D. Nuclear testing

        1. Money research

        2. Seismic energy

    E. Energy -- released when individual bonds break; their stored strain produces shock waves

V. Three types of seismic energy waves

    A. P-Waves -- Pressure or compressional

    B. S-Waves -- shear; don't go through water and/or magma

    C. Surface waves -- waves that do the damage

    D. Reading earthquakes

        1. Need three different stations around the world in order to have data to know exactly where the earthquakes has
            occurred

        2. Earthquake waves are the way we can find out what the composition of the earth is

        3. We can do this by looking at the "travel time" of P-waves and S-waves as they travel through the earth

        4. Diagram in textbook p. 40