Name Victor Paone Learning Unit 3 Volcano Review Questions This assignment is designed to assess your understanding of Unit 3 and includes some of the Questions for Review at the end of Chapters 6 and 7 from your text plus a few additional questions Each question can be answered in one to two sentences Please limit yourself to a maximum of three sentences Access the assignment complete it with ANSWERS IN A DIFFERENT COLOR FONT as a separate file and send it back for evaluation and grading through the assignment tab by or before the due date 1 In what tectonic environments to volcanic eruptions typically occur The three main places where volcanic eruptions originate are hot spots divergent plate boundaries and convergent plate boundaries 2 What changes in heat and pressure are necessary to melt rock and create magma The solid parts of Earth must heat up significantly and pressure needs to decrease in order for the heat to melt 3 How does felsic rhyolite magma form in the line of arc volcanoes like the Cascades The seduction forms the felsic magma and is defined by high silica and high gas content 4 How does lava differ from magma Magma is composed of molten rock which is stored in the Earth s crust while lava is magma which has reached the surface of the planet through a volcano 5 What are the two most abundant gases in magmas Water vapor and carbon dioxide 6 What factors influence the violence or style of an eruption There are many factors such as the composition and temperature of the magma as well as the gases which make up the magma and the amount of time since last eruption 7 What properties of mafic magma control its eruptive behavior Low silica and low gas content which the eruptions come from divergent boundaries 8 What properties of felsic intermediate magmas control their eruptive behavior High silica and high gas content in which the eruptions come from convergent boundaries 9 What causes differences in viscosity among the major magma types Differences in viscosity are caused by the friction within a fluid 10 If you visit Mount St Helens Washington you will see thousands of trees lying on the ground all parallel to one another Explain how they got that way A pyroclastic flow surge flattened the forests 11 Which of the hazards of volcanoes kill more people than anything else Why are they so dangerous Debris avalanches because the debris can cause much damage to areas where people commonly are staying 12 Why do landslides sometimes trigger explosive eruptions Landslides decrease pressure on gases in the magma and then they expand explosively 13 Which gas is heavier than air collects in low areas and can asphyxiate people or animals if it is in high concentrations Carbon Dioxide 14 An extremely large volcano with very gentle slopes is likely to be what kind of volcano and is likely to have originated from what composition magma felsic intermediate mafic A shield volcano which originated from mafic magma 15 A large steep sided volcano is likely to be what kind of volcano and is likely to have originated from what composition magma felsic intermediate mafic A stratovolcano which originated from felsic magma 16 Why do stratovolcanoes have steeply sloping sides but shield volcanoes have very gently sloping sides The basalt from shield volcanoes have low viscosity which causes the lava to become solid on gentle sloped where stratovolcanoes are more viscous causing the lava to solidify on a steeper slope 17 What is the driving force behind the explosive activity of a cinder cone They erupt where rising magma nearly encounters surface groundwater and the steam which forms creates cinders and bubbly molten lava out of the vent or crater 18 Yellowstone Park has two huge calderas each more than 20 km across How do such calderas form A volcano which previously erupted may empty a main vent of the mountain which then becomes a hollow shell and collapses inward 19 What signs precursors suggest that a volcano may be preparing to erupt Small earthquakes beneath the volcano swelling of the volcano increased emission of heat and gas 20 Harmonic tremors recorded on seismographs near volcanoes are generally interpreted as Moving magma