CHAPTER 7VOLCANOES: TYPES, BEHAVIOR, AND RISKShttp://vulcan.wr.usgs.gov/home.htmlHeliker, C. 1993, Volcanic and seismic hazards on the Island of Hawaii: Bishop Museum Press, Honolulu, 52 p.Heliker, C., D.A. Swanson, and T.J. Takahashi, 2003, The Pu’u O’o’ Kupaianaha eruption of Kilauea Volcano, Hawai’i: The first 20 years: U.S. Geological Survey Professional Paper 1676, 206 p.Sigurdsson, H. 1990, Assessment of the atmospheric impact of volcanic eruptions, in Global catastrophes in Earth History, An interdisciplinary conference on impacts, volcanism, and mass mortality, V.L. Sharpton and P.D. Ward, editors: Geological Society of America Special Paper 247.CHAPTER 7: End of Chapter Answers* climb the valley side to be above the flow4. On a huge shield volcano such as Mauna Loa, what is the main type of eruptive site? Where on the volcano is (or are) such a site (or sites)?* rift zones along the crests of three radial ridges5. Yellowstone Park has two huge calderas, each more than 20 km across. How do such calderas form?* a large mass of molten granite magma approaches the Earth’s surface. The rocks above that magma chamber sag into the magma, leaving the depression.6. How can you tell whether a plume rising from a stirring volcano contains new magma that may soon erupt?* If the plume is dark, it contains rock material. If that material is fresh volcanic glass, that indicates the presence of new magma.7. If a gigantic flow of flood basalt magma were to erupt, why might that cause a sudden increase in global warming?* A huge amount of carbon dioxide released from the basalt magma would contribute to global warming.8. How does rhyolite magma form in the line of arc volcanoes like the Cascades?* Basalt magma rising from above the subducted slab heats granitic continental crust causing melting to form the rhyolite.9. Why do the Hawaiian Islands form a chain of volcanoes?* The lithosphere carrying Hawaii slowly moves over a hotspot feeding basalt magma to the overlying volcano. As the volcano moves past the hotspot, a new volcano forms over the active hotspot.10. Scientists once believed that if a volcano had not erupted in the last 10,000 to 12,000 years, it was extinct. What evidence is there that this is not really correct? Give at least one example (be specific).* Some volcanoes erupt after still longer periods of inactivity.Examples are Mt. Lassen after 27,000 years, Santorini erupts about every 30,000 years, Yellowstone erupts about every 600,000 years.11. What evidence do scientists use to decide whether a volcano may be getting ready to erupt?* A steam or ash cloud contains shreds of fresh volcanic glass.* The flank of the volcano is bulging or tilting.* Volcanic gases show an increase in emissions of sulfur compounds or the ratio of sulfur to chlorine.* The surface temperature of the volcano is increasing.Chapter 7 - Short answer questions1. If you see an extremely large volcano with very gentle slopes, what kind of volcano is it and what is it likely made of? Be specific.* a shield volcano of basalt lava flows2. If you see in the distance, a large, steep-sided volcano, what is it likely made of, both in terms of rock composition and rock formation? What type of volcano is it?* andesite lava flows and ash; a stratovolcano3. If you see in the distance, a small, steep, smooth-sided volcano what type of volcano is it and what is it likely made of?* basalt fragments; a cinder cone.4. Why do stratovolcanoes have steeply sloping sides but shield volcanoes have very gently sloping sides?* The basalt flows of shield volcanoes have low viscosity so the lava solidifies on a gentle slops; the andesite of stratovolcanoes is much more viscous so it solidifies on a steeper slope.5. A cinder cone has a single large lava flow. Why and when does it form?* It forms after eruption of much of the cinder cone has formed. It forms because groundwater that forms steam that drives the explosive eruptions has dried out.6. What signs suggest that a volcano may be getting ready to erupt?* numerous small earthquakes, harmonic tremors, steam blasts, small ash eruptions, opening fractures, growth of a bulge, burning methane.Chapter 7 - Multiple choice questionsa. thick lava flows pile up around the ventb. a huge gas bubble released from the magma is inflating itc. the magma reacts with snow on the volcano, causing magma inflationd. the hot magma melts older ash, causing it to expand.e. * rising magma is pushing it up3. On a huge shield volcano such as Mauna Loa, what is the main type of eruptive site and where on the volcano?a. the huge collapse caldera at the summitb. at intersecting fractures at the summit of the volcano.c. * rift zones along the crests of three radial ridges extending out from the summitd. near sea level where the magma first reaches the surfacee. near the sea floor because the magma doesn’t have to rise as far4. Yellowstone Park has two huge calderas, each more than 20 km across. How do such calderas form?a. When that giant volcano erupts, it blows out the surface rocks to leave the depressionsb. When the basalt magma gets close to the surface it melts the overlying rocks leaving the depressionsc. * a large mass of molten granite magma approaches the Earth’s surface and the rocks above that magma chamber sag into itd. Coriolis effects on the near-surface magma drag the surface rocks downe. The rising, rotating magma creates a low-pressure center analogous to the eye of a hurricane.5. How can you tell whether a plume of ash rising from a volcano contains new magma that may soon erupt?a. If the plume is white, it is pale rhyolite, and therefore new magmab. If the rising plume contains solid pieces of rhyolite the volcano may be ready to eruptc. If the plume is dark and the glass in it is basalt, new magma is rising rapidly, a danger signd. * If the plume is dark, it contains rock material. If the rock is fresh volcanic glass, it contains new magmae. If the plume is accompanied by a rhyolite lava flow, the gas in the magma chamber below is still pent up and ready to blow out.6. What evidence do scientists not use to decide whether a stratovolcano may be getting ready to erupt?a. A steam or ash cloud contains shreds of fresh volcanic glassb. numerous microearthquakesc. a large bulge growing on the flank of the volcanod. an increase in sulfur oxide gas emissions from the volcanoe. * They look down the crater to see red-hot molten magma.7. In the line of arc volcanoes, like the
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