Volcanic Products and Eruptions: Homework Solution (Fall 2009) - Prof. Gabi Laske, Assignments of Natural Resources

Download Volcanic Products and Eruptions: Homework Solution (Fall 2009) - Prof. Gabi Laske and more Assignments Natural Resources in PDF only on Docsity! SIO 15 (Fall 2009) – Homework #3 20 points Due Oct. 23, 2009 Use the back of the page for answers and sketches when necessary! GIVE YOUR FULL NAME AND STUDENT ID 1. (3 pts total) Name and describe the three major groups of volcanic products/material. (3 pts). lava flows basaltic: pahoehoe (low-viscosity; flows easily; ropy structure); colder a'a' (low-to-medium viscosity; somewhat stagnant; blocky structure) andesitic: high viscosity; usually short; sometimes gets stuck in the vent and forms a lava dome clogging the vent; gas pressure can build up underground and lead to an explosion pillow lava: when lava gets in contact with water; the outer surface solidifies instantaneously; cracks force the lava to ooze out into another blob (1 pt) pyroclastic debris ash: powder size; < 2mm; sharp glassy particles lapilli or cinder: marble-to plum-size bombs: basketball-to house-size (1 pt) volcanic gases most magma contains dissolved gases, incl. water, CO2, SO2, H2S (up to 9%). Generally rhyolitic lava contains more gas than mafic lava. Volcanic gases can still escape long after an eruption and may be the only sign of volcanic activity (e.g. dormant volcanoes). Volcanic gases escape in fumaroles. (1 pt) 2. (4 pts total) What are the three V’s that influence style and vigor of a volcanic eruption? (3 pts) Would you expect more volcanic activity at a subduction zone or on a transform boundary? (1 pt) Viscosity (1 pt) Volatiles (1 pt) Volume (1 pt) Subduction Zone (1 pt) Explanation: the eruption style and vigor of a volcano depends on: * viscosity of magma (hence SiO2-content, T) * amount of dissolved gases (volatiles); e.g. the water content determines whether a magma at Hawaii will erupt as lava flow oozing out of the vent or as lava fountain * in addition to these, the volume of erupted material determines the significance of an eruption (e.g. a volcano oozing out gigantic amounts of low-viscosity lava erupting in an icelandic type eruption can become a VEI 4, due to the large volume of erupted lava; a tiny amount of high-viscosity lava may erupt in an explosion small enough to be watched safely relatively close to a volcano) You would expect more volcanic activity at a subduction zone (1 pt). Subducting oceanic lithosphere releases volatiles that melt the surrounding material in the asthenosphere; as the silicic minerals have the lowest melting temperatures the rising magma is more silicic than the source it came from. It comes to the surface in continental arcs in continent-ocean subduction zones and island arcs in ocean-ocean subduction zones. Generally NO volcanic activity near transform boundaries and continent- continent collisions 3 . (5 pts total) What is viscosity? (1 pt) Will a more viscous lava tend to be associated with