Tuesday, February 9th, 1999
Announcements: Test Thursday -- 100 points; fill in the blanks, short answers; know vocabulary, convective rates,            Pangea dates, detail, geography, etc.; Class was all review

Lecture notes:

I. Review of notes

    A. Three styles of heat transfer
            1. Conduction -- hot pot of water is taken away from its original setting and placed elsewhere, the air around the
                                       new area is then heated up because of the hot pot of water; process is very slow

            2. Advection -- take a large piece of hot material or rock and set it away from its original environment; it is like
                                    taking hot rock and placing it near a fault zone

            3. Convection -- spontaneous movement of material driven by density which is controlled by temperature; a full
                                      cycle of movement (convective system)

    B. Continental rifting -- related to sea floor spreading; occurs in three places around the world (Western US,
                                            Siberia, and the African Rift); material is pushed up from below the lithosphere which
                                            which creates a dome shape which then cracks the lithosphere and pushes the rock apart

    C. Differences between asthenosphere and lithosphere
            1. Asthenosphere -- equivalent to the mantle of the earth; like tar, very oozy and sticky; it is soft, slowly mobile:
                                            no earthquakes; can provide magma for volcanoes

            2. Lithosphere -- equivalent to the crust of the earth; very hard outer shell of the earth; hard and brittle so it can
                                       break and cause earthquakes

    D. What is viscosity?
            1. Viscosity is the abilty to flow or the stickiness of a substance (ex. Basalt has low viscosity, it flows readily like
                Hawaiian lava rivers)

    E. Isostasy -- physical condition; for example when you take an iceberg and put it into salt water a percentage of the
                          iceberg will be under the water and a percentage will be under due to its density; then take an inceberg
                          of cranberry juice and the same will happen but a different percentage of the cranberry iceberg will be
                          under the salt water than the regular iceberg

    F. Difference between active and passive margins
            1. Active margins -- experience active tectonism (subduction); it is the area near earthquakes and volcanoes;
                                            a plate boundary
 
            2. Passive margins -- do not experience active tectonism (subduction); it is the area where there are none
                                                or little earthquakes or volcanoes

    G. Obduction -- formation of an accretionary prism; scraped off slab of rock stuck on land

    H. Playa -- a broad, shallow saline (any dissolved salt) lake that eventually dries up and leaves behind playa deposits

    I. Playa deposits -- minerals left over from the dried up playa

    J. Lava types and properties
            1. Basalt (ex. Hawaii)
                    a. Comes from melting the asthenosphere (hot part of mantle)
                    b. 45% Silica ( SiO2 ), 8-10% Magnesium ( MgO )
                    c. Very dark in color
                    d. Flow properties
                            (1). Low viscosity
                            (2). Flows readily so eruptions are not as dangerous
                    e. Formed all ocean floor (Mid Ocean Ridge system and hot spots under ocean floor)

            2. Andesite (ex. Cascades, Aleutians, Lesser Antilles, Mt. St. Helens)
                    a. Has a complex origin
                    b. Involves melting of some asthenosphere and some crust
                    c. Found in the Andes (subduction--like volcanoes)
                    d. 55% Silica ( SiO2 ), 4-5% Magnesium ( MgO )
                    e. Moderate grey in color
                    f. Flow properties
                                (1). Intermediate viscosity
                                (2). May flow or explode
                    g. Formed in subduction environment
                                (1). Continent under ocean ( ex. Cascades)
                                (2). Ocean under ocean ( ex. Aleutians, Lesser Antilles )

            1. Rhyolite (ex. Yellowstone)
                    a. Comes from usually melting at continental crust
                    b. 70% Silica ( SiO2 ), 1% Magnesium ( MgO )
                    c. Very light in color (possibly yellow or white)
                    d. Flow properties
                                (1). High viscosity
                                (2). Can really blow up
                    e. Hot spot under continent (can occur along continental margins)

    K. Three types of waves
            1. P-waves -- pressure of compressional
 

            2. S-waves -- shear; don't go through water and/or magma

            3. Surface waves -- waves that do the most damage

    L. How does rheology relate to eruption style?
            1. Material with a lower viscosity will flow so it will not explode

            2. Material with a higher viscosity will explode due to pressure

    M. Black smokers
            1. Formed under the ocean in an ocean rift environment

            2. Water descends then flows back up through a crack in the lithosphere and takes minerals with it; the hotter
                the water and the more acidic the water, the more minerals the water will take with it; hot water solution
                of minerals then hits cold water at the surface and the minerals and elements then crystallize and cause the
                water to appear black from the sulfide material

    N. Phreatomagmatic -- explosion in volcanic system ( ex. Mt St. Helens ) where snow and/or ground water helps
                                        with the explosion; when hot magma hits the snow it cause a reaction therefore causing an
                                        explosion; the ash mixes with the snow (ash-laden snow) which is very detsructive ( Columbia
                                        10 years ago )

    O. Intra-plate volcanism -- within the plate as opposed to plate margins along the ring of fire; intra-plate occurs in areas
                                              outside the margins like in Hawaii (caused by hot spots)

    P. Ophiolites -- portions of mantle and ocean crust; sometimes primary source of asbestos and other harmful things

    Q. Accretionary prism -- found in subduction; it is the material not "subducted" down; it is triangular pieces of rock
                                           that keep increasing in size because of the continous process of rock adding onto it